Category Archives: Universe & Cosmology

Horizons Out of Reach

Imagine you are walking on a terrain of rolling hills; in the distance you can see the horizon. Beyond that point you don’t know what you’ll find. When you arrive at the crest of a hill a whole new landscape appears with its own horizon. This is a common metaphor used to show how knowledge is usually acquired. Each horizon reached often presents another horizon (or question) in the distance.

The story of science is one of impressive discoveries. Many horizons have been reached, but many more are yet to be encountered. No one knows how far we can go and what we will find. I hesitate to limit what might be possible, because science has surprised us time and time again. If the human race survives long enough, is there anything we can’t find out? I would think that there are some questions we will not be able to answer, but which ones? One should think long and hard before ruling anything out, which I have done. For what it’s worth, I am left with two questions which appear out of reach. I’ll get back to this later but first a little context.

Horizons Reached

At present the knowledge base is immense, but it had to be acquired. Imagine going back 100, 500 or 1,000 years and contemplating the future. It’s possible that some future discoveries could have been predicted. However, there are other findings that few saw coming. It is practically impossible to provide a full account of impressive scientific discoveries. However, there are some that immediately stand out. What follows has been mentioned in prior blogs of mine; think of it as a short list of scientific highlights:

  1. The Idea of Natural laws: At around 500 BC the ancient Greeks documented the concept of natural laws. They suggested that patterns in nature could be recognized and attributed to natural laws. This was a major breakthrough in scientific thought.
  2. The Copernican Revolution: In 1543 Nicolaus Copernicus published his theory of the heliocentric model of the universe. He removed the Earth from the center of the known universe and replaced it with the Sun. This was a significant reality check, which would influence human philosophy for years to come.
  3.   Newton’s Laws: In 1687 Isaac Newton disclosed his law of universal gravitation and his three laws of motion. Newton laid the foundation for what later became known as classical physics. Now over 300 years later, Newton’s equations still apply (except for extreme circumstances).
  4. Einstein’s Relativity: With special relativity (in 1905) and general relativity (in 1915), Albert Einstein filed in the gaps in Newton’s laws. Einstein accounted for those extreme circumstances. His contribution led to a greater understanding of the large-scale universe.
  5. Darwin’s Theory of Evolution: Charles Darwin provided an explanation for how all life evolves with his famous publication in 1859. This one basically speaks for itself; few if any discovery is more impressive.
  6. Revealing the Atomic and Subatomic Realm: Beginning in the early 1900s, several people worked on theories such as quantum mechanics and the standard model of partial physics. A realm previously inaccessible was shown to be real and would unwittingly have a significant impact on human affairs.
  7. The Big Bang: In the 1931 George Lemaitre suggested that the universe began in a single geometric point. He arrived at this by applying general relativity to the observations of William Hubble. Lemaitre`s idea would eventually provide us with a truly universal origin story. 
  8. DNA: In 1962 James Watson, Francis Crick and Maurice Wilkins won a Nobel Prize in medicine for the discovery of the structure of DNA. This opened up a whole new science, which will undoubtedly impact us for generations.

Of course the list above could be significantly longer and still fall short. However, I present it just to give you a feel for how knowledge, particularly scientific knowledge, alters our perception of the world. It is debatable how many past discoveries could have been foreseen; nonetheless one can imagine some horizons in the distance which may be attainable. For example: figuring out how life on Earth began, or the discovery of life elsewhere in the universe. Closer to home, there is finding a cure for cancer (or most cancers), and maybe even weather forecasting weeks or months in advance. No one knows for sure which findings are coming, but I feel fairly certain that at least two questions will remain unanswered.

Contemplating the Unanswerable

The two questions I am referring to are as follows: 1) Why is there a universe in the first place?  2) Why is the universe the way it is and not some other way? Another question which I feel I must address before moving on to question 1, is this: Why is there something rather than nothing? You’ve probably heard this one before, and it is similar to question 1. However, I find it to be a peculiar question and here’s why. First let’s define what is meant by nothing. If by nothing, one assumes the absence of everything, then nothing is a non-entity. In other words, how can nothing be a reality if by definition nothing has no existence. The question gives us two options, something or nothing and it seems to me that something is real and nothing is not. By this logic one could conclude that there has to be something, but why a universe?

For some the existence of the universe doesn’t seem to be a big problem to solve. The standard answer is that God created the universe and that’s it. However, I can’t help but ask two simple follow-up questions: a) Why is there a God in the first place? b) Why is God the way he (she, it) is and not some other way? Do you see how this works, by inserting God as the explanation for the universe we’ve circled back to where we started. In essence the questions are identical. We have merely moved the starting point from the universe to God.

Another approach is to examine the possibility of a multiverse. There are scientific reasons that suggest that other universes may exist, but that is as far as it goes.  Although the multiverse is theoretical, it may shed light on question 2. Why is the universe the way it is and not some other way? If multiple universes actually exist, it could be that all possible universes exist, therefore it is not surprising that at least one universe is like ours. Although the multiverse idea is somewhat satisfying on the surface, it has its problems. For starters, it does not address question 1. Why is there a universe in the first place? It says nothing on why there would be a multiverse in the first place.

There is also the problem of testing the multiverse idea scientifically. How can we ever verify something outside the boundaries of our vast universe? Hypothetically, even if our science advanced to a point where universes outside our own could be detected, how could we know the full-scale of a multiverse? We would likely be unable to determine how many universes exist in total. Ultimately that’s where I think the multiverse idea falls short in terms of answering question 2. Why is the universe the way it is and not some other way? If we can’t know how many universes exist in total, we can’t explain why our universe is the way it is and not some other way. All possible universes have to exist in order for the multiverse to the job. Or at the very least, it would take an extremely high number of universes.

Why is there a universe in the first place and why is the universe the way it is and not some other way? I have thought about these two questions philosophically, religiously and scientifically and have made little progress. Each approach gains momentum only to fall short. There are undoubtedly still many horizons within our reach and it will be interesting to see what lies ahead. That being said, I have to conclude that there are at least two horizons that seem to be hopelessly out of reach.

References:http://www.bbc.co.uk/schools/gcsebitesize/science/add_edexcel/cells/dnarev3.shtml

https://www.quora.com/What-is-the-relationship-between-the-Standard-model-and-Quantum-field-theory


 

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The Physics of Time?

Our conception of time as moving in one direction, from past to present to future, is so commonplace that we accept it as fact. But what if our experience of time is misleading us, and perhaps hiding the true reality of the universe? Can we rely on our senses to accurately perceive something as abstract as time? Is time real, or just an illusion caused by other physical effects? Can science provide any clues into understanding time?

It was once thought that time existed as absolute and unchanging, flowing at a constant rate and moving in one direction. This was true for scientists and the public alike. Isaac Newton considered time in much the same way as space; time and space providing the arena in which the universe unfolds. Newton’s famous laws of gravity and motion assumed absolute space and time. His laws work extremely well for our corner of the universe, that which is accessible to human senses. They are still used today to calculate the gravitational forces of the sun, moon and planets, as well as the motion of spacecrafts and objects close to earth.

There is a catch, however; Newton’s laws are not 100% accurate. Absolute space and time is not an acceptable assumption when dealing with extreme scales of the universe, a reality that was hidden from Newton in his time. The modern laws of physics question our everyday concept of time. In the early 1900s, Einstein devised the theories of special relativity and general relativity, and the idea that space and time could be flexible was born.

Einstein’s Revision of Newtonian Time

More than 300 years ago Isaac Newton wrote that, “He did not need to define time because it is something well known to all.” For obvious reasons our common sense perception of time has been called Newtonian time. The concept of absolute time had gone unchallenged until Einstein came along.

With Einstein’s revision of Newton’s ideas we have to envision a universe where each celestial body and each observer (what concerns us) carries their own clock with them. With relativity, the passage of time is relative to influences of mass and motion. In short, massive objects like stars and planets cause space and time to warp, resulting in gravitational effects and slowing down time. Also, time elapses slower for an object in motion than for an object at rest; the discrepancy in the passage of time gets proportionally larger as the speed increases. Even though it can be said that time runs at different rates (or two observers disagree on the passage of time), each perspective is equally valid. When one observer moves relative to another observer, clocks will not agree.

Flexible time is a property that applies everywhere in universe, however, the effects are minuscule in everyday life. Although the effects of relativity are not visibly apparent to us, observations have confirmed that this is how the universe really works. The scientific evidence is conclusive; time is relative, not absolute. Just as one can move through space, one can also move through time. No longer could space and time be considered as two separate entities; a new term called spacetime was brought into use to better account for the relationship between the two.

A hypothetical situation of an alien in a distant galaxy shows how bizarre relative time can be. If you are stationary here on earth and the alien moves away from you, the alien’s now coincides with a moment in your past. If the alien turns around and moves towards you, then the alien’s now coincides with a moment in your future. Just as extremes in speed and gravity alter the passage of time, extreme distance has a similar effect on what constitutes a given moment of time for two observers. This is the kind of universe that Einstein described.

I cannot think of a better everyday example of flexible time than GPS devices. The clocks in the satellites in orbit need to account for the fact that clocks on the Earth run a little bit slower. This is due to the combined effects of the motion of the satellites and the gravity on earth (the Earth’s gravity having the largest effect). If not for the application of relativity, GPS devices would quickly become inaccurate.

The Laws of Physics, Entropy and The Arrow of Time

Whether we examine small physical systems or the universe as a whole, there is no arrow of time found in the laws of physics. For example, if a scientist knows all the current conditions, he can determine precisely what happened in the past or predict a future outcome. This can be achieved by applying the same laws either backward or forward in time.

Is there anything in science that indicates an arrow of time? There is a concept in physics called entropy, which may give us an arrow of time. Simply stated, entropy is the measure of disorder, and the implication of entropy is that physical systems move towards a direction of increasing disorder. The reason being, that there are many ways in which disorder can come about. Conversely, there are few ways that order can be achieved.

Let’s take the example of the pages of a book (all numbered in order). If we were to randomly mix up the pages (and re-stack them) the chances are extremely high that the pages will end up disordered. In only one configuration will the pages be ordered, while many arrangements will be disordered. In almost all cases it takes a special effort to create order and no effort at all to create disorder.

The puzzle is: how has the universe created stars, galaxies, planets and life on earth? If entropy rules, you would think that the universe would be in chaos forever. To get an answer we may have to go back to the birth of the universe. The Big Bang is believed to have been a highly ordered event (perhaps the most ordered state of the universe). From that point on the universe has evolved into greater disorder. Entropy may give us an arrow of time. From the point of most order (in the past) towards increasing disorder (in the future).

This should make us pause and consider our present conditions on earth. Conditions favorable for life are extremely difficult to come by, and entropy is bound to rule in the end. In the grand scales of the universe, in both time and space, life is a newcomer and rare (as far as we know). Life on earth is destined to be extinguished, at least at some time in the far future.

Our experience shows us that many things only happen in one direction, and usually in the direction of more disorder. For example: A glass can fall to the ground and break, but a glass can’t reassemble by itself. A drop of ink can mix in water, but the ink can’t come back together into a drop. An egg can be broken, but can’t reassemble back into the shell. This is entropy at work, and possibly the scientific reason behind our common-sense experience of an arrow of time.

The River of Time

Clearly, there is a sense that time moves from past to present to future, like a river, which flows in one direction from one moment to another. From the present perspective the past is gone forever and the future is yet to be realized. However, for physicists it is not as clear cut. From Einstein’s perspective, what constitutes a given moment of time is dependent on the observer. Because time is relative to each observer, my now could coincide with a past or future experience of someone else in a far-away galaxy. There is no sense that the whole universe progresses at the same rate. There is no now that everyone can agree on.

How could this be? As long as there are discrepancies in time for different locations and observers, there can be no universal now for all. Equally, there can be no past or future moment that all can agree on. If this is true the implications are unsettling: All moments of the universe exist. From a physicist point of view Brian Greene concludes in The Fabric of the Cosmos:

” … if you agree that your now is no more valid than the now of someone located far away in space who can move freely, then reality encompasses all of the events in spacetime… Just as we envision all of space as really being out there, as really existing, we should also envision all of time as really being out there, as really existing, too.”

Einstein also saw the paradox between physics and experience: “For we convinced physicists, the distinction between past, present, and future is only an illusion, however persistent.”

Does time really flow like a river? Even from a common sense perspective the distinction of past, present and future is relative to the individual. For me, someone who lived many years ago existed in the past. Someone that will live 100 years from now will exist in the future. That’s all from my perceptive or from my point of reference. From the perspective of a historical figure, like Einstein, he lives in the present and I will exist only in the future. With each moment there is no essential difference, no temporal absolute, just the relative perspective of each individual.

Change as The Scorekeeper of  Time

If I haven’t created enough doubt as to your assumed notion of time, I will conclude with one more observation. This has to do with change. Is it possible that the only real aspect of time is change? At least could change be the only way that time is perceived?

We notice time has elapsed because something has changed. It is reinforced by our mind. Our memories tell us that an event was in the past, and our imagination projects that something could happen in the future. In essence, we experience the passage of time or that time flows because of continual change. If there were no change at all, would time even exist? Imagine a universe with every object being still or no objects at all. Every moment would be identical.

A reality with no change is not our experience, nor is it how the universe presently works. However, a particular question about the Big Bang Theory may shed some light: That is, what happened before the bang? Science can’t take us back any further, as the Big Bang represents a theoretical barrier. Perhaps we don’t need to look further. Physicists believe that time and space as we know it were created at the Big Bang. This may be highly speculative, yet it could be that there was no change before the Big Bang; or conditions were so chaotic that there would have been no discernible events. Thus, that would mean that nothing really happened before.

At the other end of the spectrum, one current model of the universe predicts that space will continue to expand at an increasing rate. This expansion will drag every galaxy farther apart with no end in sight. Far, far into the future everything in the universe will become diluted. In the end, if we can call it that, everything will decay, leaving only random particles drifting in space. The universe will be cold, dark and practically empty. We could even conclude there will be no change and time will also come to an end.

Coming up with an explanation for time is challenging. You could even make a case that time does not exist. What we experience as time may be something else altogether. With each perspective of time I have mentioned there is something intriguing, and still something seems to be missing. How could something as familiar as time be explained differently, with each explanation having some merit? That’s how it appears to me.

Newtonian time aligns very well with our daily experience of time. Einstein’s relativity is in agreement with modern observations of the universe. Entropy gives us an arrow of time not found in the laws of physics. The river of time points to everyone’s unique frame of reference. And finally, change gives us a physical component that marks the passage of time.

 

References: Brian R. Greene, The Fabric of the Cosmos (New York: Alfred A. Knopf, 2004), 139.

The Fabric of the Cosmos: The Illusion of Time, Life Sciences, Published on Apr 12, 2016. https://www.youtube.com/watch?v=pPA83Ap0Xsg.


 

Evidence for the Big Bang Theory

We are all aware of the Big Bang Theory, but how much is known about the strength of the theory. For some the Big Bang is a vague and far-out idea, for others it is a T. V. sitcom. Nonetheless, it requires some background to appreciate how the Big Bang Theory became what it is today.

The Story Begins

Isaac Newton is credited for saying: “If I have seen further than others, it is by standing upon the shoulders of giants.” Newton was implying that his discoveries would not have been possible, without the brilliant people (giants) which preceded him. The Big Bang is such a theory, it was pieced together by several individuals spanning decades of work. Or perhaps a few centuries of work, it all depends on when one chooses to begin the story.

I will arbitrarily begin in 1687 when Newton published his Principia Mathematica unveiling his law of universal gravitation and his three laws of motion. Newton was the first to provide a mathematical framework to account for the effects of gravity, thus he could calculate the motion of the moon and planets. Gravity was also the force responsible for keeping objects firmly on the Earth or causing an object (such as an apple) to fall to the ground.

Newton’s laws have stood the test of time; however, they are not 100% exact and serve as a very close approximation. They are, however, practically exact for our experience of everyday events. Only in some extreme situations do they fall short. Also, Newton was forced to concede that he did not know the mechanism behind the force of gravity. In simple terms, Newton was able to calculate the effects of gravity even thought he was unable to provide a complete explanation for how gravity worked. Nevertheless, Newton’s laws were a major scientific breakthrough for its time and started the ball rolling in the right direction.

Dynamic Space

Image converted using ifftoanyIt wasn’t until 1915 when Albert Einstein came up with his Theory of General Relativity, which addressed some of the gaps in Newton’s understanding of gravity. Einstein was able to explain gravity in detail, as a consequence of curved space. The mass of bodies (such as planets and stars) bend the fabric of space, thus generating the attraction. The fact that space has dynamic qualities, which can expand and curve would later become important to the big bang concept.

Also significant, is that General Relativity predicts that the universe should be either contracting or expanding. However, in Einstein’s time the prevailing wisdom was that the universe was static and eternal. Einstein gave way to convention, and after the fact, arbitrarily added a figure in his equations known as the cosmological constant. This was a repulsive force with just the right value to counter the effects of gravity, thus keeping the universe stable. As it turned out, Einstein’s original prediction of a non-static universe was later proven correct. He then dropped the cosmological constant from his theory.

Measuring the Night Sky

After Einstein’s General Relativity it was left to astronomer Vesto Slipher, who worked at the Lowell Observatory in Arizona. Slipher took spectrograph readings of distant stars and discovered that the light emitted was moving away from us. The starlight was shifted to the red end of the spectrum. Slipher was the first to realize that receding light is red shifted and in coming light is blue shifted. This was an indication that the universe was not static after all; however, his work went unnoticed at the time. Slipher was not aware of General Relativity and his findings would only have an impact a few years later.

henrietta-swan-leavittAnother breakthrough came from a woman named Henrietta Swan Leavitt. She worked at the Harvard College Observatory as a computer, as they were known in those days. These women studied photographic plates of stars and made computations. Leavitt was able to establish Cepheid variables as standard candles; a method to determine the intrinsic brightness of a star. Cepheids are elderly stars which pulsate at regular intervals; these stars brighten and dime in a very reliable pattern. Leavitt worked out that these stars could be used to calculate distances. For the first time, there was a method of measuring the large-scale universe. Today, Type 1A supernovae are also used as standard candles. Similar to Cepheids, Type 1A supernovae are said to have intrinsic brightness, making them reliable measuring tools.

Building a Case

edwin-hubbleThe story now shifts to the Mount Wilson Observatory in California. Equipped with a new telescope Edwin Hubble was able to make use of Slipher’s red shifts and Leavitt’s standard candles. In the early 1920s Hubble discovered that some of the starlight he observed was coming from distant galaxies. Before this finding the only known galaxy was our own. Today we know that there are well over 100 billion galaxies in the visible universe alone. In an instant, Hubble had shown that the universe was much bigger than anyone had theorized.

Roughly a decade later, Hubble made an equally stunning discovery. By observing distant galaxies, he determined that they were all moving away from us. The only exception to this was our own local cluster (close enough in proximity to be held together by gravity). All galaxies were moving away from us on average. In short, the universe was expanding in all directions! Furthermore, the distance between galaxies and the speed at which they were moving were proportional. For instance, galaxies twice as far away were moving twice as fast, three times as far away, three times as fast. Interestingly, debris from an explosion shares a similar signature. This is because the further away from the epicenter the debris comes to rest, the faster it has to travel.

george-lemaitreJust as Slipher before him, Hubble had little understanding of General Relativity and failed to recognize the full significance of his discovery. It took a Belgian priest and scholar named Georges Lemaitre to put it all together. He applied General Relativity to Hubble’s findings, wound the clock backwards, and in 1931 he suggested that the universe began in a single geometric point. This was the original idea, which later became known as the Big Bang. Nevertheless, the world was not yet ready for Lemaitre’s bold idea. It took a few more decades before Lemaitre’s idea became an established scientific theory.

In 1964 the Big Bang Theory was finally confirmed by observation. Two Bell Laboratory scientists named Arno Penzias and Robert Wilson were testing a microwave detector. They were receiving interference coming from all directions. After ruling out a number of possibilities, it was determined that the signal was coming from outer space. In fact, they had discovered the cosmic microwave background radiation. They had accidentally stumbled upon the echo of the Big Bang.

The cosmic microwave background (CMB) is the remnant of light from the Big Bang. It had been predicted earlier, but now it was confirmed by observation. Due to the expansion of space, this light has been stretched to the microwave part of the spectrum. From its extremely hot beginning, the temperature of the CMB has now cooled to 2.7 degrees above absolute zero (nothing can be colder than absolute zero). No matter where we look the temperature of the CMB varies by less than a thousandth of a degree. These temperature measurements imply a common origin. How else could microwave radiation, separated by vast distances, have practically the same temperature (everywhere) unless it originated from a common event?

Evidence for the Big Bang (Recap)

  • Receding Starlight- By measuring the red shift of distant stars Vesto Slipher discovers that distant stars are moving away from us, suggesting that the universe is not static.
  • Establishing Cepheid Variables- Henrietta Swan Leavitt finds a way to make use of pulsating stars to measure distances in the large-scale universe.
  • Expanding Universe- Edwin Hubble discovers that the universe is expanding proportionally in all directions.
  • Compatible with General Relativity- Albert Einstein’s famous theory predicts a non-static universe and allows for space to bend and expand (necessary for the big bang concept).
  • The Smoking Gun- Arno Penzias and Robert Wilson stumble upon the cosmic microwave background radiation (the echo of the big bang). The Temperature of the CMB varies by less than a thousandth of a degree.

Note: There are also other pieces of evidence which point to a Big Bang that requires a background in particle physics to appreciate (which I do not have), so I have left it out here.

Interesting Facts About the Big Bang

  1. The Theory begins a tiny fraction of a second after the bang. The known laws of physics cannot be applied prior to the theoretical beginning of time. What happened before is uncertain.
  2. The Big Bang created time and space as we know it, calling into question the idea of a before.
  3. At the Big Bang the universe was at its hottest; it has been cooling ever since.
  4. At the beginning, the universe was in its most orderly state. From the moment of its origin, it has been moving towards higher disorder.
  5. The universe was in its simplest form at the Big Bang; it has been growing in greater complexity since its birth.
  6. There is no such thing as the center of the universe. From any given galaxy an observer would see the same thing; all galaxies would be moving away on average.
  7. Galaxies don’t move through space, it is the space itself which is expanding and carrying the galaxies along.
  8. The term ‘Big Bang’ was coined by astrophysicist Fred Hoyle. It was meant as a put down for a theory he never accepted and the term stuck.
  9. Arno Penzias and Robert Wilson won a Nobel Prize for their discovery of the CMB; something they were not even looking for.
  10. If you tune a T. V. to a channel that is not broadcasting, 1% of the snow on the screen is due to the cosmic microwave background. So if you ever complain that there is nothing to watch on T. V., you can always disconnect the cable and watch the Big Bang.

 

References: Bill Bryson, A Short History of Nearly Everything (London: Black Swan, 2004).

Mark Henderson, Joanne Baker, Tony Crilly, 100 Most Important Science Ideas (United States: Firefly Books, 2011).

Dec. 30, 1924: Hubble Reveals We Are Not Alone, Randy Alfred, 12.30.09, https://www.wired.com/2009/12/1230hubble-first-galaxy-outside-milky-way/

Scientific America, What is the Cosmic Microwave Background Radiation? October 13, 2003, https://www.scientificamerican.com/article/what-is-the-cosmic-microw/


 

The Moon: Our First Satellite

moonWhen one thinks of a satellite it is usually in the form of a man-made object orbiting the Earth. However, by definition a satellite is a moon, planet or machine which orbits a planet or a star. From our vantage point here on Earth, the Moon is the predominant satellite. Long before Sputnik 1 (the first man-made satellite launched by the Soviet Union) the Moon was our one and only satellite.   

Long, Long Ago

When the Solar System first formed it consisted of a star surrounded by a disk of gas. Eventually this gas gathered into dust, rocks, asteroids and finally planets. Each planet also had its own disk of gas, which in turn would follow a similar process. Some of the debris was pulled into the planets, but not all. Over time some of the gas eventually turned into moons. Some moons could have formed independently from their host planet, and later were captured by gravity as they drifted through space.

Our Moon is believed to have been created by a different manner. The early Solar System was a very violent and chaotic place. As planets and moons were born, they were bombarded by asteroids and small planets. The Moon’s many craters is clear evidence of this early chaotic period. In the 1970s a theory was proposed: about 4.5 billion years ago the Moon was formed by a gigantic collision between the early Earth and another planet. Recently a new theory has surfaced which tweaks the original 70s theory. I’ll begin with the established theory first, then get back to the revised theory later.

earth moon collisionThe original theory states that a mars-size planet on a similar orbit as Earth struck the Earth on an angle. The collision created the Moon and quite possibly the tilt of the Earth’s axis of 23 degrees. This rouge planet is sometimes referred to as Theia, named after the mother of the ancient Greek moon goddess, Selene. The impact generated intense heat in both planets. The Earth absorbed part of Theia along with her heavy iron core, the lighter rocky material ended up in a ring around Earth’s orbit. From this debris our first satellite would from. Interestingly, the Moon may have been intact after only several decades. Over billions of years both bodies cooled, but not entirely; the Earth still has a largely molten core. The smaller Moon may have completely cooled or perhaps still retains a tiny molten core.

 Evidence for the ‘Giant Impact Theory’ (70s theory)

  • The Moon is large for a satellite in comparison to the size of the Earth. Most moons are much smaller in ratio to the planet they orbit. Models for how moons are usually formed place a limit on how big a moon can be in relation to its host planet. Our Moon appears to be too big to have formed by surrounding gas in the early solar system or captured by the Earth’s gravity.
  • By examining the surfaces of both Mercury and Mars we are able to see what the early solar system must have been like. Virtually unchanged for about 4 billion years, these planets are dotted with craters. Some of which are as large as six hundred miles wide. The Earth has no such markers due to climate and erosion, but by deduction, we can assume that the early Earth was also hit by large objects.
  • In six trips to the Moon the Apollo astronauts collected rock samples and for the first time they were able to see what the Moon was made of. Remarkably, the Moon samples were found to have a similar chemistry to Earth. This discovery is in line with a Theia and Earth collision. Such an event would have blasted parts of the Earth into space which coalesced with bits of Theia to form the Moon.
  • The impact hypothesis was also put to the test with computer simulations. The impact suggested, was applied to software that recreated the conditions of the early Solar System. After running several simulations of a Mars-size object colliding with the Earth at the angle predicted, everything worked. The end result was the Earth/Moon system we have today.

The ‘big Whack’ (new theory)

This is where the new revised theory comes in; modern computer simulations suggest a much more intense collision at a significantly sharper angle. Such an intense impact would have vaporized Theia and much of the Earth. This  accounts for why the Earth and Moon are so similar in their chemistry. In fact, new research is finding increasing chemical similarity. This points to a much more violent impact which would have thoroughly mixed both bodies before they separated.

Also, the impact forced the Earth to spin much faster (about once every 2 hours) and tilt as much 60 to 80 degrees on its rotational axis. The Earth’s present rotational tilt of 23 degrees is though to have been arrived at later by complex interactions with the Moon and the Sun. Another interesting fact, which the original theory left unexplained, is the 5 degree tilt of the Moon’s orbital plane. The Moon’s orbit is tilted 5 degrees in relation to the Earth’s orbit around the Sun. The Earth orbits the Sun on what is called the ecliptic plane; this plane is where most bodies orbit the sun. The early Moon’s orbit is though to have matched the severe tilt of the Earth and did not transition smoothly to match the ecliptic plane. The revised theory proposes that the 5 degree orbital tilt of the Moon is but a relic of a much steeper orbital tilt from the distant past.

A Match Made in Heaven?

earth and moonThe two prominent heavenly bodies are the Sun and the Moon. Much of the Sun’s influence on the Earth is clearly recognizable; the Moon, however, affects us in more subtle ways. The warmth of the Sun (or lack of it on some days) is an everyday experience. In ancient times the Sun was worshiped by some cultures as godlike. It would have been clear then, as it is now, that without the Sun the Earth would be void of heat and most likely without life.

As it turns out the Moon’s presence might also be fundamental to life. However, for a large part of human history the Moon remained mysterious. Today scientists speculate that the Moon may have contributed to life in various ways. What follows are plausible explanations for how our Moon influenced life:

  • When the Moon was first formed it was much closer to the Earth than it is today. It is still receding by a minuscule amount every year. Over 4 billion years ago the Moon exerted a greater gravitational pull on the Earth, which may have set plate tectonics in motion. Plate tectonics are believed to be necessary for a living planet.
  • Shortly after the Earth’s post impact formation it rotated about once every 5 hours (70’s theory) or once every 2 hours (new theory). Either way, the Moon’s presents gradually slowed down the Earth’s rotation, diminishing the severity of the weather. The Moon may also have stabilized the earth’s rotation on its axis.
  • Nocturnal animals behave differently at various times during the monthly lunar circle, depending on the brightness of the Moon. If not for the influence from varying moon light, who knows how the course of evolution would have been altered.
  •   The greatest influence the Moon has on the earth is in generating tides. This would have allowed life from the ocean (where life began) to spend short intervals of time on land. This may have provided the ideal training ground for life to gradually adapt to the land.

ocean tidesThe Earth and the Moon have been united by gravity for over 4 billion years. It is hard to know for sure what the Earth would be like without the Moon. Would there be life? If so, what would it look like? Nevertheless, if there was no Moon and life did manage to evolve, it would almost certainly be different.

 

References: Jim LeBans, The Quirks & Quarks Guide to Space.

Did We Need The Moon For Life? Fraser Cain, Published on Nov 20, 2015, https://www.youtube.com/watch?v=KulEmr7X1HM

Origin of the Moon, tonyweston9, Uploaded on Nov 27, 2008, https://www.youtube.com/watch?v=m8P5ujNwEwM

What is a Satellite? Dan Stillman, Feb 12, 2014, http://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-satellite-k4.html

Scientists propose new theory about how Earth got its moon, By Sheena Goodyear, CBC news, Posted: Nov 1, 2016. http://www.cbc.ca/news/technology/moon-theory-1.3830623

Violent Impact That Created Moon Mixed Lunar and Earth Rocks, By Charles Q. Choi, Space.com Contributor | January 28, 2016 02:28pm ET. http://www.space.com/31763-moon-creating-impact-mixed-lunar-earth-rocks.html

Did Early Earth Spin On Its Side? Monday, October 31 2016. http://www.seti.org/seti-institute/press-release/did-early-earth-spin-its-side

New Model Explains the Moon’s Weird Orbit, October 31, 2016, http://cmns.umd.edu/news-events/features/3680


 

The Anthropic Principle

the astronomerWhy are we here? This is perhaps the most fundamental philosophical question. One can imagine contemplating this question at any time in human history. Many stories have been inspired by this question, usually taking the form of myths, or religious and spiritual traditions. Today, ‘why are we here’ is also a scientific question. The anthropic principle arose as a response to the question of human existence. The idea was first proposed in 1973 by theoretical astrophysicist Brandon Carter. Since then it has been expanded and stated in several forms.

What is the Anthropic Principle?

The word anthropic is defined by the Merriam-Webster online dictionary as: “Of or relating to human beings or the period of their existence on Earth.” That’s a start. For simplicity I will stick close to Brandon Carter’s original formulation, which he expressed as two variants. I will paraphrase based on the description from a few sources:

  1. The Weak Anthropic Principle refers to our special location in the universe (both in time and space), which is conducive to our existence. The fact that we can observe the universe means that planet Earth must have the conditions necessary for our existence.
  2. The Strong Anthropic Principle refers to the fundamental laws of physics, which are precisely set for our existence. The strong principle takes into account the properties of the universe as a whole.

The Burden of Proof

habitable zoneIn a vast universe it is not surprising that a planet, like the Earth, has a special location (usually called a habitable zone or a Goldilocks zone). The specific laws of the universe needed for human life are more difficult to explain (usually called fine tuning). Using a legal metaphor, the strong anthropic principle has a greater burden of proof than the weak anthropic principle. In this case, burden of proof is a figure of speech, because the anthropic principle is as much a philosophical idea as a scientific one. 

In The Grand Design, Stephen Hawking and Leonard Mlodinow describe the weak anthropic principle as an environmental factor. They write:

“Environmental coincidences are easy to understand because ours is only one cosmic habitat among many that exist in the universe, and we obviously must exist in a habitat that supports life”

The strong anthropic principle is all-encompassing and generally more controversial. Hawkings and Mlodinow go on:

“The strong anthropic principle suggests that the fact that we exist imposes constraints not just on our environment but on the possible form and content of the laws of nature themselves”

Stating the Obvious or a Profound Insight

Is the anthropic principle a satisfying explanation? On the surface, it seems like an obvious statement that explains very little. But as I reflect on the idea, I am not so sure. Maybe it is suggesting something profound. Perhaps the answer to why we are here is simple: it could not be otherwise.

Lawrence KraussFor example, Lawrence Krauss provides an anthropic interpretation to one of the universe’s properties. In the book, A Universe from Nothing, he examines the relationship between the energy density of matter and the energy density of empty space. Yes, space has energy and it can be measured. The density of matter in the universe can also be measured. It turns out that now is the only time in cosmic history that both values are comparable. That’s a curious result.

The universe has been expanding since the big bang, and as it expands the density of matter decreases. Matter gets diluted as galaxies get farther apart from each other. Meanwhile the energy in empty space remains constant (there is nothing to dilute or increase in empty space). Therefore at the time galaxies formed the density of matter was greater than the energy in empty space. That’s a good thing, because the gravitational effect of matter was dominant, which allowed matter to come together.

However, if the values for matter and energy had been comparable at the epoch of galaxy formation, galaxies would not have formed. Empty space exerts a repulsive force, which would have canceled out normal attractive gravity. Matter would not have clumped together. Krauss writes in A Universe from Nothing:

“But if galaxies hadn’t formed, then stars wouldn’t have formed. And if stars hadn’t formed, planets wouldn’t have formed. And if planets hadn’t formed, then astronomers wouldn’t have formed!”

It seems highly coincidental that the energy values for matter and space are roughly equal now, but they could not have equalized too much earlier. Otherwise, no one would be here to observe it. Similarly, if one of a number of physical properties were slightly different, we would also not be here. That’s when anthropic reasoning steps in: An observer must observe the conditions of the universe that allows the observer to exist.

astronomersMaybe a change of perspective is needed: Instead of focusing on our present circumstances and looking back, we can look at the evolution of the universe. Life is a latecomer to the process, of which an incalculable series of events occurred. Our existence is the result of all that came before. Although it does appear that the universe was made for us, it is in fact, the universe that made us. We were formed from the conditions that were set long before conscious beings could observe any of it.

Is Physics an Environmental Science?

The traditional approach of physics is to discover and understand the universe we live in. The fundamental laws and the values for the constants of nature are consistent throughout the observable universe. The physical laws discovered on Earth can be applied to the universe as a whole. But there can only be one exact set of laws and history that allow for our existence. That’s unless our universe is not the only one.

For some, recent scientific evidence is suggesting that there are many universes (a multiverse). Others point out that inferring a multiverse is not science; because by definition other universes cannot be observed directly (they would exist outside our observable universe). If we apply the strong anthropic principle to the multiverse theme, it does partly explain the exact parameters of our universe.

If the cosmos is populated with many universes, possibly infinite universes, then the laws of physics could be purely random. They would simply emerge as an environmental consequence. Some physicists have compared the multiverse to a foam of bubbles (each bubble representing a universe). The laws could be different in every bubble of an endless cosmic foam. Some bubble universes could be similar to ours, others vastly different.

Of course, this is a hypothetical argument. Nevertheless, if we could observe every universe in a multiverse, every single one would be finely tuned for its own existence. Anthropic reasoning would state that there is nothing special about our universe. In all the non-life generating universes there is no one to observe them, in ours there is. It’s that simple. Obviously, the anthropic principle (inferring a multiverse or not) is not a proven argument, but it’s one of many possible answers to the question: Why are we here?

 

References: Stephen W. Hawking and Leonard Mlodinow, The Grand Design (New York: Bantam Books, 2010), 155.

Lawrence M. Krauss, A Universe from Nothing (New York: Free Press, 2012).


 

How Could We Discover Alien Life in The Universe?

exoplanetOf all the so-called big questions, perhaps none inspires more curiosity than the following: Is there life elsewhere in the universe? The question leads to many other questions, speculations, possibilities and impossibilities. In recent years science has made tremendous progress towards understanding the universe, both in what is out there and how it came to be. The number of stars and galaxies is enormous, and we now know that many stars have planetary systems (nearly 2000 exoplanets have been discovered). Some planets outside our solar system are believed to be earth-like, in size, composition and location in relation to their host star.

Recent discoveries have shown that other locations in the universe may have conditions similar to Earth. Our galaxy, the Sun and the Earth are not unique. That said, the Earth supports life due to a series of coincidences that may be unique. Still an unimaginably large cosmos presents many opportunities for life-giving conditions to align. This means that the possibility for alien life may be greater than once thought. There seems to be 3 ways in which humans could discover extraterrestrials: 1) Searching the universe for life. 2) Sending signals in outer space so aliens could intercept them. 3) Aliens discovering us. Let us examine these possibilities a little further:

Searching the Universe for Life

mars roverNumerous unmanned space probes have explored our Solar System. The firsts space probes to visit other planets were launched in the sixties, even before the first lunar landing. By the seventies probes were reaching the outer planets, and in 2015, New Horizons made its historic Pluto flyby (the farthest planet when I was in school). Several rovers have landed on Mars, transmitting images and analyzing soil samples (the first successful mission was in 1976). Presently, the rovers Opportunity and Curiosity are still operating on Mars.

Scientists have discovered much about the composition of the planets and their moons, including evidence for liquid water. A few moons of Jupiter and Saturn are believed to contain oceans of liquid water beneath their icy surfaces. And in October 2015, NASA made the announcement that liquid water flows on Mars. A number of conditions are necessary for life to exist, but liquid water is a must for all known life on Earth (the starting line in the search for life). At least if life exists somewhere without water, it would be to foreign for us to imagine.

If there is alien life in our Solar System, it would be simple life and probably microbial; but what about intelligent life? How far do we have to look? The Solar System is merely our cosmic neighborhood.

In 1995, the first exoplanet was discovered and many more followed. The existence of the planets is inferred by studying minor changes in starlight, which are caused by the presence of planets; however, the distances involved are immense. The closet star system is Alpha Centauri (a 3 star system), which is 4.25 light years away. By comparison it takes about 8 minutes for the Sun’s light to reach the earth. The Milky Way alone is 100,000 to 120,000 light years in diameter, and contains over 200 billion stars. Beyond our home galaxy, there are over 100 billion galaxies in the observable universe.

By numbers alone, it seems that the opportunities for extraterrestrial life are endless. But the odds against discovering alien life seem equally as great. At this time indirect evidence is all we have. For example: exoplanets that may be located in habitable zones or distant regions that have chemical compositions similar to our Solar System. Maybe all we will find is information or signals which have to be decoded, and conclusive evidence may never be found.

Sending Signals in Outer Space

Humans have been inadvertently sending signals to the universe since the first radio and television broadcasts. By now the signals have reached thousands of star systems. However, they travel as electromagnetic waves and will go undetected unless someone has an appropriate receiver at the other end. Even if the signals have crossed advanced civilizations, what are the chances that they have built earth-like technology? There is also the evolutionary timeline to consider. Could some civilizations be too early in their development, or could others have long gone extinct?

Attempts were made to purposefully send messages to outer space. In 2008, the Beatles song “Across the Universe” was broadcasted towards Polaris (the North Star). But even traveling at light speed the signal will take over 300 years to reach its destination. And if we get a reply, it will take another 300 years.

voyager 1The space probes Pioneer 10, Pioneer 11, Voyager 1 and Voyager 2 have completed their missions exploring the planets, and have left the Solar System (speeding away indefinitely). They all contain time capsules, with information about humans and our location in the universe. Incidentally, the well-known image of the pale blue dot was taken by Voyager 1 as it left our Solar System; a snapshot of the earth from 6 billion miles away.

Sending space probes into interstellar space solves one problem, but creates another. On the one hand they are concrete objects (not like radio waves), on the other hand they travel much slower than radio waves. For example, the nearest star system is 4 light years away (that’s 4 years for a radio signal). By comparison, it will take 70,000 years for the space probes to travel the same distance. Either way, the odds appear slim that our messages will ever be noticed.

Aliens Discovering Us

alienIt is possible that aliens have already discovered the Earth; they may even have tried to communicate with us. Some people believe that aliens have visited the Earth, but for a logically minded person the stories are far-fetched. From a scientific perspective, there is no evidence to support such claims. Everything scientists know about space travel makes alien visitations practically impossible. The distances are simply too great; it would take hundreds of generations to make the voyage (unless aliens have lifespans of a 1,000 years or use teleportation and wormholes, though we shouldn’t believe everything we see in Star Trek).

The most likely form of alien contact would be indirect, such as something moving at light speed, like an electromagnetic wave. An alien space probe sent many years ago would be a possibility, however, it would be a tremendous stroke of luck to pass anywhere near the Earth. Then again, it depends on how many probes are out there. The odds of being found or finding something is proportional to how many are looking. Therefore, we don’t know if humans are the only species looking to the stars for life.

A Numbers Game

By studying the light spectrum of distant galaxies, astronomers have discovered that the chemistry of the universe is similar throughout. In addition, at the largest of scales the universe has evolved basically the same everywhere. The Earth has intelligent life because of a series of fortunate events (fortunate for us); it could also have occurred elsewhere. Or maybe a very different form of life evolved due to totally different circumstances.

For example, take the Earth’s distance from the Sun as one of many specific variables. The Earth is about 93 million miles from the sun, just the right distance to allow for liquid water. To appreciate how precise the location is, the change from summer to winter is caused by a 23.5 degree tilt of the earth’s axis. As the Earth orbits the sun it either tilts towards (in summer) or away (in winter) from the sun. That’s it. Of course the northern and southern hemispheres have their seasons in reverse relation to each other.

So is the existence of life simply a numbers game? Given the unimaginable size of the universe, is it inevitable that conditions will be just right somewhere else? With the number of planets that likely exist, even if the odds for life were a billion to one, there would still be life on a billion planets. If I had to make a call, I think the odds are good that there is life elsewhere in the universe. However, the odds are slim that we will ever discover it. The distances involved present challenges that may be too much to overcome.

 

References: Big Picture Science: Life in Space, April 20, 2015.

Big Picture Science: How to Talk to Aliens, January 12, 2015.

Universe Today: 10 Facts About the Milky Way, by Matt Williams, http://www.universetoday.com/22285/facts-about-the-milky-way/ December 3, 2014.

Universe Today: What is the Closest Star, by Fraser Cain, http://www.universetoday.com/102920/what-is-the-closest-star/ June 14, 2013.


 

Nature’s Fine Tuning and the Multiverse

numbersThere are a number of fundamental physical constants of nature, in which their values seem to be finely tuned. Examples of  such constants are: the speed of light, the strength of gravity, the mass of the elementary particles, and the strength of the atomic forces. The fine-tuning angle comes into play when one considers the exact parameters of the constants. Hypothetically, if one were to adjust the values just a little bit, the universe would be vastly different. This fact alone does not present a problem. However, physicists have noted that minor changes to the values of the constants would not allow life to develop. It is as if the universe knew we were coming, or is it?

The values of the physical constants are critical for giving our universe the structure that it has. For example: the precise strength needed to hold the atomic particles together in stable arrangements, and the gravitational force needed to clump matter into stars and planets. If the strength of gravity was slightly weaker, matter in the early universe would have spread apart too quickly; thus preventing stars from forming. Conversely, if the gravitational force was a little stronger, matter would have come together too quickly and everything would have collapsed. It is clear to scientists that gravity, as well as other values, could not be adjusted very much without erasing the possibility for life.

The Most Extreme Fine Tuning

Although the apparent fine tuning of the constants demand an explanation, nothing compares to the level of fine tuning of one particular constant. This is called the cosmological constant (also called dark energy), and it represents the value of the energy in empty space. The cosmological constant is believed to exert an outward force, which is causing the universe to expand at an accelerated rate. In 1998, the value of the cosmological constant was measured by two teams of astronomers. The number they came up with is extremely small, a decimal point followed by 122 zeros and a one (measured in Planck units).

The energy in empty space, represented by the cosmological constant, is only relevant at the largest of scales. As the universe expands the amount of space is also increasing, thus increasing the effect of the dark energy. But in the distant past when the universe was much smaller, the total energy in space would have produced a far lesser effect. And here is the catch. If the outward push of the cosmological constant was slightly larger by a few decimal points, it would have counteracted the pull of gravity too quickly. This would have prevented stars, planets and galaxies from forming. In this scenario life would not exist.

By removing just a few zeros from an already small value, a universe suitable for life would disappear. Physicists are at a loss to explain why the number is so small and so finely tuned for our existence. In addition, the value of the cosmological constant revealed by observations is far less that what theory predicts. That is, the theory of the microscopic realm (quantum mechanics) predicts that the energy in empty space should be much larger. The mismatch between theory and observation does not sit well with physicists, as it shows that there is something missing with this picture.

Possible Solutions

The specific values of the physical constants require an explanation. Some people will look for a metaphysical solution. This will usually imply a creator for the universe who setup the constants for a purpose. The word God is the preferred choice, and it suggests that the universe was planned for our existence. Yet for others, crediting God for designing the universe in a special way is a non-explanation. One would still have to explain where God came from and why he was there in the first place.

Another line of reasoning would be to accept that mere chance accounts for the constants. But given the amount of fine tuning, this seems akin to winning a lottery with an infinite number of combinations. Chance alone is not a very satisfying solution. There is also the possibility that we don’t have enough information to solve the problem. Maybe a deeper understanding of the laws of physics is needed, and someday physicists will find the answer.

 The Multiple Universe Proposal

multiverseThe word universe has traditionally been used to describe all that exists. However, cutting-edge physics is requiring that a change of perspective is needed. Through a variety of physical discoveries the idea of multiple universes is being considered. The words parallel universes, parallel worlds, alternate universes, multiverse and others are being used. In the multiple-universe theme, the word universe has a slightly different meaning. Universe no longer means all there is, but rather means a region of a larger cosmos that is separated from other regions.

Physicist and science writer Brian Greene states, in The Hidden Reality, why the concept of multiple universes is compelling:

” The subject of parallel universes is highly speculative. No experiment or observation has established that any version of the idea is realized in nature… That said, I find it both curious and compelling that numerous developments in physics, if followed sufficiently far, bump into some variation on the parallel-universe theme.”

Although not yet experimentally tested, having large numbers of universes (possibly infinite) could explain the fine tuning of the physical constants. The logic is simple. With many universes, with different possible values for the constants, it is likely that one has the values we observe. Therefore, it is not surprising that we find ourselves in a universe that allows life. In the universes that have conditions that don’t allow life, there is no one to observe them, no one to say that they are not finely tuned for life.

As Brian Greene suggested, there are several theories in physics that imply a multiverse. The reasoning is technical, though I will list a few examples, which point to the possibility of a multiverse:

  • Eternal Cosmological Inflation: The extreme burst of spatial expansion at the early moments of the universe is known as inflation. Inflation is a cosmological principle, which in theory could happen anywhere, thus giving rise to multiple big bangs.
  •  A Spatially Infinite Cosmos: By inferring an infinite expanse of space-time, there is a limit to ways particles of matter can be arranged. Conditions in one location would eventually have to repeat somewhere else, creating parallel universes.
  •  The Extra Dimensions of String Theory: String theory proposes that at the tiniest of scales there exist extra spatial dimensions. It also states that there are many possible shapes for the extra dimensions of space. However, string theory cannot determine which of the shapes corresponds to our universe. If string theory is correct, the different possible shapes for these extra dimensions could be realized in different universes.
  • The Many-Worlds Interpretation of Quantum Mechanics: The atomic/subatomic realm is governed by randomness and understood using probabilities. Interpretations can vary. The many-worlds interpretation states that all the possible outcomes associated with quantum mechanical probabilities really happen, resulting in parallel worlds.

parrallel universeNot all the multiple universe proposals would yield different values for the constants. Some would produce exact replicas of our universe, or very close copies. Hence the term parallel universe. Yet other proposals would allow for different laws of physics or different values for the constants. These could be universes that are totally foreign and barely recognizable to us.

Whether we live in one of multiple universes is anyone’s guess. Presently, there is no known method that could observe them. Nevertheless, there are plenty of cases where physical theories or mathematics have pointed toward a phenomenon in nature, even before it was observed. And then at some later date, observations confirmed the theory. Therefore, if modern physics is suggesting the existence of a multiverse, it provides an interesting argument for the fine tuning of the physical constants of nature.

 

References: Brian Greene, The Hidden Reality (New York: Alfred A. Knopf, 2011), 8, 9.

Leonard Susskind – Is the Universe Fine-Tuned for Life and Mind? (Closer to Truth), Published on Jan 8, 2013. https://www.youtube.com/watch?v=2cT4zZIHR3s

 The Fabric of the Cosmos – Universe or Multiverse (Published on July 16, 2014) https://www.youtube.com/watch?v=ib0RNqVusoU


 

The Cosmological Constant: From Einstein to Dark Energy

EinsteinThe cosmological constant has its humble beginnings with Albert Einstein’s theory of gravity. In 1915, after a decade of working on some unsolved issues regarding gravity, Einstein completed the theory of general relativity. Today, this is still the best theory we have for describing how gravity works at large scales. Nevertheless, 2 years later (in 1917) Einstein made a small adjustment to the equations of general relativity. He introduced a term called the cosmological constant, which represented a repulsive force to counteract the attractive force of gravity.

Einstein realized that general relativity would require the universe to either be expanding or contracting, however, the belief at the time was that the universe was essentially static and eternal. Because gravity causes large structures to attract each other, logic would deduce that the universe as a whole should be contracting. But this was neither observed nor part of conventional thinking. The cosmological constant, a repulsive force with just the right value, allowed the universe to remain static. Although the cosmological constant was present in all of space, Einstein provided little details concerning what this mysterious force actually was.

Einstein’s Greatest Blunder

In 1929, Edwin Hubble carefully studied light from distant galaxies. He calculated the distance of the galaxies by examining the luminosity of a specific type of star, known as a Cepheid variable. The light from a Cepheid displayed a distinct pulsating pattern, which could be used as a distant indicator.

Hubble expanded on the work of astronomer Vesto Slipher, who was the first to observe the redshift of distant galaxies (although they were called spiral nebula at the time, because it was not yet known that other galaxies existed beyond our Milky Way). The redshift meant that incoming light waves were stretched, indicating that the observed light was moving away. This provided evidence that the galaxies were moving away from the earth. And even more significant, Hubble found that all galaxies were also moving away from each other.

Hubble’s observations confirmed that the universe was expanding. Upon learning the news, Einstein went back to his equations and removed the cosmological constant, as it was no longer needed to maintain the former belief of a static universe. It has been reported that Einstein called the cosmological constant his “greatest blunder.” Despite Einstein’s claim, the cosmological constant would resurface many decades later, but it came as an unexpected turn of events.

The Universe is Accelerating

galaxyAs of 1998 the expansion rate of the universe over cosmic time was still unknown. Either the universe would continue to expand forever, or the gravitational effects of galaxies would cause the expansion to slow down and perhaps stop. If at some time the expansion did stop, then it would stand to reason that gravity would cause the universe to collapse. This would lead to something like the opposite of a big bang (a big crunch).

The rate of expansion will determine the future fate of the universe. But how can one determine the expansion rates at different time periods? How can we know how the current expansion rate compares with past rates? Fortunately, the universe is extremely large and extremely old. Light from faraway galaxies can take millions and billions of years to reach the earth. This allows astronomers to go back in time and examine galaxies as they were in the past. The light we see now was emitted many years ago; these stars and galaxies appear as they once were.

Two international teams, one lead by Saul Perlmutter, the other by Brian Schmidt, set out to determine the expansion rate over cosmic time. They applied some creative methods based on a specific type of exploding star, called a Type Ia supernova. At the end of their lives these particular stars explode in a consistent pattern, which signal an intrinsic brightness. The astronomers determined a star’s distance from earth using the information from a Type Ia supernova. Then they calculated the redshift of the star’s host galaxy, and made the calculations with a number of galaxies at various times in the past.

Accelerating universeThe two teams eventually arrived at the same conclusion. The galaxies are currently receding faster than they were in the distant past; the universe is accelerating! This was an unexpected result, as it was mostly assumed that the expansion was slowing down over time (due to the attractive force of gravity).

The Return of the Cosmological Constant

If gravity is an attractive force, then what could be causing the universe to speed up. Enter the cosmological constant or its reincarnation, dark energy. Einstein’s hypothesis of a repulsive force that was counteracting gravity may not have been far off base (though his reason for introducing it was misguided). An unknown form of energy in empty space seems to be responsible for the acceleration of the universe. It has been dubbed dark energy because it does not emit light, but it could also be a term that points to the mysterious nature of this type of energy. Dark energy does, however, make up 70% of the total energy of the universe. Remarkably, this has been calculated and it seems to describe the universe we live in.

One more point of note: Since dark energy/cosmological constant is presumed to occupy all of space, its overall influence increases as space expands. Therefore in the distant past, when the universe was more condensed (relatively speaking) attractive gravity was dominant. The expansion of the universe slowed down at some point. However, as space swelled and galaxies moved farther apart, the dark energy caught up and then surpassed gravity as the dominant force. The tables turned, causing the universe to speed up.

Current evidence supports a cosmic story in which the universe will continue to expand practically forever. Galaxy clusters, like our local group, will still be held together by normal gravity, because they contain enough matter. However, in the far future all evidence from beyond our local group will disappear. The universe will be comprised of a bunch of island universes.

 

References: Mysteries of a Dark Universe: Uploaded on Oct. 31, 2011. https://www.youtube.com/watch?v=QUpWCRadIIA

Brian R. Greene, The Fabric of the Cosmos (New York: Alfred A. Knopf, 2004).


 

Decoding Light to Unlock the Secrets of the Universe

prism Much of what we know about the large-scale universe is due to decoding signals from light. The light that reaches the earth from faraway galaxies arrives as a wide spectrum, which is much more than visible light (or white light). Light is actually an electromagnetic wave with a range of wavelengths. White light is but a tiny band in the middle of the spectrum of wavelengths. When white light is refracted, such as passing through a prism, we see the colors of the rainbow.

If we move past the red band the wavelengths get longer, from infrared to microwaves to radio waves. Moving towards the opposite side of the spectrum, past the violet band, the wavelengths get shorter, from ultraviolet to x-rays to gamma rays. Even though the large majority of light is invisible to us, scientists have instruments that can detect information from the spectrum. The following list shows 5 things we know about the universe from decoding light.

1) The Contents of the Universe

Exploring the universe started simple with just visible light; ancient astronomers gazed at the night sky with the naked eye. All the twinkling yellow dots basically looked identical. They could not determine the size and distance of objects. The advent of the telescope added detail to the night sky, such as differentiating stars from planets and discovering individual galaxies.

Space telescopes, like Hubble and Kepler, are now placed in the earth’s orbit. From above the atmosphere, these and other instruments are collecting a tremendous amount of details about the universe. For example, the Hubble Space Telescope focused on a dark spot in the sky for a period of 10 days. In this tiny patch (roughly the opening of a drinking straw) an image of 10,000 galaxies was produced.

2) The Existence of Extrasolar Planets

In recent years, over 1,700 planets outside our solar system have been discovered (some of them are earth-like). Most planets orbit stars, therefore planets can be detected by examining changes in starlight, which are caused by existing planets. Astronomers use a number of methods to find planets. The two most effective methods are:

  1. The transit method: By observing a star for a period of time a planet will occasionally pass in front of the star. Viewed from earth, a planet will cause the starlight to dim slightly, thus announcing the planet’s presence.
  2. The Doppler method: As a planet orbits a star it exerts a gravitational effect on the star, which causes the star to wobble slightly. This can be detected by examining variations in the light spectrum as the star moves towards or away from the earth.

3) The Chemical Composition

Light from distant stars and galaxies can be converted into a spectrum of colors. This is achieved with an instrument called a spectroscope, which is attached to a telescope. This is perhaps the most valuable tool for decoding light. As it pertains to the chemical composition of the universe, a particular property of light contains precise information from its source.

When the light spectrum of a star is displayed by a spectroscope, vertical lines (called absorption lines) appear at specific locations, depending on the elements contained in the star. Each element produces a unique pattern of lines, which can be matched with experiments in a laboratory. Even though the information contained in the spectrum will be from a number of elements, the distinct pattern of each element can be sorted out.

Absorption lines

Absorption lines

By studying the information from light, astronomers have found that all the stars in the universe have more or less the same chemistry (including our sun). Thus, knowing that all the elements originate in stars, the chemical composition of the universe is essentially the same everywhere. The elements found here on earth are plentiful in other galaxies as well, leaving us to speculate that other life-sustaining planets may be out there.

4) The Universe is Expanding

There is another valuable piece of information from the spectroscope that has transformed our view of the universes. It is called a redshift. When the spectrum from distant galaxies is examined, the vertical lines are shifted towards the red end. This is due to the Doppler effect or the Doppler shift, and it has to do with the nature of waves. Light is a wave, and similar to sound waves, incoming waves will be stretched when the source is moving away; thus causing the absorption lines to shift towards the red end of the spectrum.

Redshift

Redshift

The conclusion from this information is that galaxies are moving away from us. The universe is expanding. The exception to this rule is that nearby galaxies are not expanding, because they are held together by gravitational forces. But for the universe as a whole, galaxies are moving away from each other. In other words, the earth’s location is not unique; the view from any location in the universe would be similar. Incidentally, it is actually the space that is expanding. The galaxies are rushing away because they are being pulled by the swelling of space.

5) The Big Bang

There are 3 ways we can get to a big bang origin of the universe by studying light:

  1. The expansion rate: The universe is expanding at a defined rate (based on the redshift), which is simply stated as: distant galaxies that are twice as far away from us are moving twice as fast, and galaxies that are 3 times as far are moving 3 times as fast. This means that if we reverse the timeline, in the distant past all the galaxies would converge at a point of infinite density. This was the moment of creation.
  2. The cosmic microwave background radiation: The CMBR is the remnant of the intense energy that was created at the big bang. The light from the big bang event has propagated throughout space, and is presently detectable as microwave radiation. Although the radiation is now faint, it is present in all directions of space.
  3. The agreement between prediction and observation: The amount of lighter elements (hydrogen, helium, deuterium and lithium) that are now present in the universe agrees with the predictions of the big bang theory. The quantity of these elements were detected from light coming from old stars and distant galaxies. The amounts are consistent with what the theory predicts would have been created in the early universe.

From an everyday perspective, light illuminates the world and we see things as a consequence. However, when we examine the large-scale universe our eyes alone are not sufficient. It is remarkable that light from very far away contains information from its source. And if not for ingenious techniques in decoding light, figuratively speaking, we would forever remain in the dark.

 

References: Richard Dawkins, The Magic of Reality

Lawrence M. Krauss, A Universe from Nothing

Stephen Hawking’s Universe -101- Seeing is Believing (June 14, 2013) https://www.youtube.com/watch?v=5kgPxvJqvEA
The Big Bang: Observational Evidence (June 4, 2012) https://www.youtube.com/watch?v=8WaI-iIlgdI


Discovering the Nature of Gravity

Of course we all know what gravity is. It’s the force responsible for making objects fall, keeping our feet firmly planting on the ground, and maintaining the moon’s orbit around the earth. But by what mechanism does gravity accomplish these tasks? Surely there are no invisible strings of a master puppeteer. The full story behind understanding the force of gravity spans at least 400 years. Three giant steps have led to modern physics’ current picture.

Heliocentric Modle

 Step 1: The Copernican Revolution, Galileo and Kepler

Just before he died, in 1543, Nicolaus Copernicus published his famous work describing the heliocentric model of the universe. Although he had formulated his theory years earlier, he delayed publishing until the end of his life. This was probably because he feared criticism from contemporaries or retribution from the church. Placing the sun at the center of the known universe (as opposed to the earth) was a revolutionary idea for its time. This was a monumental leap in the early scientific age.

The idea that the earth moved went against common sense and intuition. In reality, whether the sun moved or the earth moved could not be determined by visual means. Sometimes science has to rely on other methods; in this case, the daily/monthly movements of the planets had to be charted and analyzed.

An object can only be said to be in motion in reference to something else. For example, if you are on a boat that is departing from a large dock, and you look to your side, you will see the dock moving. For an instant you will think that the dock is moving. Then you realize this can’t be true. You may feel the boat rocking or accelerating, but from a visual point of view you can’t tell which is moving.

Years later, Galileo adamantly supported Copernicus’ view and took the brunt of the attack from the church. He was sentenced to house arrest, where he spent the last decade of his life. Nevertheless, Galileo’s contribution to science extended much further than the celestial model. He was instrumental in establishing observation and experimentation as pillars of scientific reasoning. It was becoming clearly that there was order and predictability in nature, which was accessible to human analysis.

Johannes Kepler also lived in Galileo’s time, and he was able to calculate the motion of the planets using mathematics. His most famous work is known as the laws of planetary motion, a precursor to Newton’s laws. In the process he calculated that the orbits of the planets were not perfect circles as originally thought. But rather moved in elongated circles called ellipses. Although the movement of the celestial bodies were being charted in great detail, there was still no comprehensive theory of gravity.

 Step 2: Newton’s Insights

Newton's Cannon

Newton’s Cannon

Issac Newton imagined a cannon perched on a mountain top and asked himself the following question: what would happen if cannon balls were fired at steadily increasing speeds? The first few balls would start out in a straight line and then fall to the earth in a curved trajectory. However, if he kept going, something peculiar would happen. The curved path of the cannon ball would eventually match the curvature of the earth. The cannon ball would be in perpetual free fall, and orbiting the earth.

This was the key insight. The same force that was responsible for maintaining the orbits of the moon and planets also caused an apple to fall from a tree. No one had thought of this before. At least if someone had, it did not become public knowledge.

Therefore, the story that Newton got his idea of gravity when an apple fell on his head may not be true. He could have been thinking about cannon balls. But having a cannon ball fall on his head does not make for an inspiring story. What followed was a mathematical unity of both the heavens and earth, his laws of motion and universal gravitation. In spite of Newton’s great achievements, he still had no clue what gravity actually was. It would take more than 200 years for someone to come up with the answer.

 Step 3: Einstein’s Imagination

Among many things, Albert Einstein was famous for his thought experiments. He imagined physical scenarios, which he tried to figure out what would happen and how it could be explained. Perhaps this is how he came up with his picture of gravity.

In 1915, ten years after his theory of special relativity, he published the theory of general relativity. As it relates to the actual cause of gravity, the answer is as counter intuitive as the earth moving through space. The gravitational effects are caused by the properties of space itself; just as Einstein had shown that time was flexible (in special relativity), space was also flexible.

It is the warping or curving of the fabric of space that make objects fall and maintain the orbits of celestial bodies. It is similar to the effect of a large rubber sheet (like a trampoline). If one were to place a large heavy ball at the center of the sheet, any smaller balls would be drawn to it by the warping of the sheet (caused by the heavy ball).

Warps in Space

Warps in Space

Orbits will be created when a balance is established between the motion of a body and the distortion of the spatial fabric. That’s it, distortions in space caused by massive bodies, not a pull or push is responsible for gravity. This theory goes beyond Einstein’s imagination; it has been confirmed by scientific observations. It took 400 years of investigation to understand the basic property of one of the most familiar forces on earth.

 

References: Richard Dawkins, The Magic of Reality

The Elegant Universe 1 of 3 Einstein’s Dream (Published on Jun 21, 2012) https://www.youtube.com/watch?v=UV_X2B5OK1I

Stephen Hawking’s Universe -101- Seeing is Believing (June 14, 2013) https://www.youtube.com/watch?v=5kgPxvJqvEA