Tag Archives: special relativity

The Universe Revealed Through Modern Science

Physical laws have existed since the beginning of time, but they had to be discovered for science to become relevant. Scientific knowledge was built mainly by a series of small advances and adjustments, however, a few major discoveries by a few scientists have altered the course of the scientific endeavor. The age of modern science was pioneered by men like Copernicus, Galileo and Kepler. They began to examine the patterns in nature, and discovered that in some situations the workings of nature could be explained, and even predicted. They found that nature’s harmony was governed by physical laws, which were at least partly accessible to human comprehension. They studied the motion of objects on earth, and then turned their attention to the heavens. They charted the movement of the celestial bodies in great detail, and discovered that the motion of the celestial bodies could also be predicted. The gateway to scientific discovery had been opened—the universe would soon begin to reveal its most profound secrets.

In the early years, it was Isaac Newton’s insight that stood above all others. He discovered gravity as the force responsible for the motion of the moon and the planets. And as the story goes, the same force responsible for an apple falling from a tree. In 1687, he published the Principia Mathematica, where he disclosed his law of universal gravitation and the three laws of motion. It was a major breakthrough in advancing the scientific cause. Newton’s laws provided the foundation for what has become known as classical physics. For more than 300 years his equations have stood the test of time. In fact, Newton’s equations were all that was needed to plot the course that placed men on the moon. Although his equations provided an accurate mathematical framework (actually a very close approximation that was later revised by Einstein), Newton had no idea what mechanism was responsible for the effects of gravity. It is also believed that he regarded space, the arena of motion, to be absolute and unchangeable. He viewed time in much the same way.

It was not until the early 1900s when the mysteries of space and time, as well as the underlying causes of gravity, were addressed. Albert Einstein changed the course of history when he published his theories of special relativity (in 1905) and general relativity (in 1915). Einstein formulated that space and time are not absolutes, but have dynamic qualities associated with mass and motion. In fact, he described space and time as a unified whole, which later became known as space-time.

With special relativity, Einstein showed that measurements of time (and even distance) could differ for two observers, based on their relative motion. Time will elapse slower for someone in motion than it does for someone at rest. And the discrepancy in elapsed time will increase as the difference in the speed increases. In a sense, observers carry their own clock with them. This realization signifies another important point—that the observers would also disagree on what constitutes a given moment in time. One person’s now would be different from the other person’s now, yet both perspectives would be equally valid. Keep in mind, that it’s only when dealing with speeds approaching the speed of light or extreme distances that disagreements in time become significant. The effects of special relativity are not visibly apparent in the temperate conditions that exist here on earth; however, the earth is somewhat of an anomaly in comparison to the universe as a whole. With the universe, where extreme distances and speeds are commonplace, special relativity becomes important.

With general relativity, he showed that the effects of gravity are caused by the warping or curving of space (or space-time, but for simplicity I will use the term space). Heavy objects like planets and stars warp the fabric of space, thus creating the effects of gravity. It is similar to placing a heavy ball in the center of a trampoline. Any smaller balls placed on the surface will be drawn to the center, due to the surface being warped by the heavier ball. Bear in mind that a trampoline is a two dimensional representation of what is actually a three dimensional spatial fabric. It does, however, give us a clear visual analogy of how curved space participates in the motion of celestial bodies. In the case of planets and stars, orbits will develop when a stable balance is achieved. The earth can be thought of as moving in a straight line along a curved surface of space. Or as taking the path of least resistance along the distorted spatial fabric, which is created by the sun’s presence.

Another consequence of general relativity is that just as gravity curves space, it also curves time. But what does curved time mean? Similar to special relativity, where motion alters time, general relativity claims that gravity also alters time. When gravity exerts its influence time slows down. For instance, time passes a little slower on the surface of the earth than it does for objects high above the earth. A practical example of this effect is in the technology behind global positioning systems (GPS). The satellites that guide GPS devices have to account for both special and general relativity (general relativity producing the largest effect). The internal clocks of the satellites account for the fact that clocks on the earth’s surface run slower. If not for these adjustments, GPS devices would quickly become inaccurate; the coordinates on the ground would drift off by several kilometers each day.

Einstein’s relativity goes against our common sense perceptions, but apparently this is the reality of the universe. Einstein’s insights led to modern cosmology (the study of the origin and evolution of the universe), and our current view of the universe. Both classical physics (Newton’s view) and relativity (Einstein’s view) provide a deterministic framework. That is, if the present conditions are known, the past and future conditions can also be determined. That’s assuming that you have all the present data and the mathematical ability to do the calculations.

The next scientific breakthrough would be of a very different nature. In the mid-1930s a group of scientists were unlocking the secrets of the atom. In so doing, it led to the development of quantum mechanics. They found that the atomic and subatomic realms behave in ways that are very different from the world experienced at the larger scales. A whole new set of laws had to be developed to deal with the bizarre nature of the atom—laws that are partly governed by randomness and probabilities. Physicist Brian Greene describes the nature of quantum mechanics. He writes in The Fabric of the Cosmos:

 “…according to the quantum laws, even if you make the most perfect measurements possible of how things are today, the best you can ever hope to do is predict the probability that things will be one way or another at some chosen time in the future, or that things were one way or another at some chosen time in the past.”

The probabilities that are used in quantum mechanics are more fundamental than the probabilities that are assigned to everyday events. When we assign a probability to a game of dice or blackjack, it is based on our inability to calculate the precise conditions that will determine the outcome of the event—specifically, each roll of the dice or flip of the card. With quantum mechanics, however, even if we know all the present information possible, we still can not predict a future outcome with absolute certainty. Quantum physics describes a reality that is fundamentally uncertain, in which objects have no definite position, take no definite path, and even have no definite past or future.

Some experiments (known as the double-slit experiment and variations of it) have actually shown that a single particle, such as a light photon, can behave as if it simultaneously takes a number of different paths from a source to a target. It is debatable whether this really happens; nonetheless, outcomes are determined by the number of possible paths of the photon, whether or not they are all realized. The photon takes a definite position only when it is observed or measured (when it strikes the target). In between the source and the target, it can be thought of existing as a haze of possibilities.

This is partially explained by the idea that subatomic objects, like photons and electrons, exhibit both wave-like and particle-like properties. At times, a photon or electron can be described as occupying a wide region in space, and at other times described as occupying a single point in space. Depending on the variation of the double-slit experiment, a photon can sometimes behave like a wave and sometimes behave like a particle. Although it is not entirely clear how these results should be interpreted, physicists agree that our conventional sense of reality does not apply at the quantum level—even to a larger degree than Einstein’s relativity.

I know this all sounds absurd. Nevertheless, the predictions of quantum mechanics have produced results that are extraordinarily accurate. Quantum mechanical predictions are accurate in the sense that if a sufficient number of identical experiments are carried out, the totality of the outcomes will reflect the assigned probabilities. Yet each single experiment will generate a random and unpredictable outcome. Therefore, even with the most precise calculations possible, there is an unavoidable degree of uncertainty in quantum mechanics.

It has been said that nobody understands quantum mechanics, that even scientists that work with quantum mechanics don’t understand it. So if it’s not sinking in, don’t lose any sleep over it. In summing up: the renowned physicist Richard Feynman once wrote in The Strange Theory of Light and Matter “[Quantum mechanics] describes nature as absurd from the point of view of common sense. And it fully agrees with experiment.”

Once again our common sense is challenged by the laws of physics. From classical physics to the updating of relativity, and the weirdness of quantum mechanics, reality is proving to be difficult to grasp, as these theories give us very different views of reality. For this reason, there is a consensus among some physicists that there exists a deeper level of reality to the universe that remains undiscovered. They propose that there should be one theoretical framework that describes the universe, and not a fragmented view based on several partial theories. Einstein called this hypothetical theory a unified theory (also called the theory of everything). The quest for a unified theory became one of Einstein’s passions during his later years; however, it was not realized during his lifetime.

Today, physicists are still seeking the elusive unified theory. Our present understanding of the universe is based on the two major breakthroughs of the 20th century. 1) General relativity, which describes the large scale structures of the universe, like stars and galaxies. 2) Quantum mechanics, which describes the small scale structures, like molecules and atoms. These two theories have been very successful in their own right, but in some extreme situations they cannot be applied successfully. In some situations where large densities are compressed into a tiny region of space, an understanding of both the large and the small is required. But when general relativity is applied together with quantum mechanics, the theories fall apart. This becomes a major obstacle when trying to understand conditions such as the center of black holes and the origin of the universe where these conditions need to be considered. The big bang theory describes the events a fraction of a second after the beginning, but says nothing about the beginning or before. Without a unified theory, or a new theory altogether that can deal with this situation the cause for the origin of the universe will remain a mystery.

As we have seen, each new discovery has added a piece to the puzzle and our understanding of the universe has increased dramatically over the years. The ultimate goal of science can be nothing other than a complete understanding of the laws of nature, though it may be that mystery will forever be a part of the picture. In his 1988 book, A Brief History of Time, Stephen Hawking weighs in on the subject:

“But can there really be such a unified theory? Or are we perhaps just chasing a mirage?

There seems to be three possibilities:

1) There really is a complete unified theory, which we will someday discover if we are smart enough.

2) There is no ultimate theory of the universe, just an infinite sequence of theories that describe the universe more and more accurately.

3) There is no theory of the universe; events cannot be predicted beyond a certain extent but occur in a random and arbitrary manner.”

There may very well be limits to what humans are able to understand, but this should not limit our quest for knowledge. Where would we be today if some people hadn’t questioned conventional thinking and opened the door to greater discovery? It is due to the few who dared to challenge the beliefs of their time that many benefited. Not only in science, but in other domains as well, it is the quest for knowledge that paves the way for progress. This is the case for our lives, as well as humanity as a whole. No one knows how far we can go, and only time will tell. On this note, we can at least rest assured that the modern age of science has brought humanity out of the darkness of ignorance, and into the light of knowledge.

References: Brian R. Greene, The Fabric of the Cosmos (New York: Alfred A. Knopf, 2004), 10-11.

Richard Feynman, QED: The Strange Theory of Light and Matter (Princeton: Princeton University Press, 1988).

Stephen W. Hawking, A Brief History of Time (New York: Bantam Books, 1988), 165-166.


 

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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.