Category Archives: Physics

Electromagnetism and the Modern Age

If one had to rate the greatest discoveries of all time, electricity would rank high on any list. Most of the modern world is powered by electricity. What would our lives be like without electricity? Just think of your own home; when the power goes out everything gets put on hold. Take people’s smart phones away and they don’t know what to do with themselves.

The application of electricity was the result of 3 centuries of investigation and experiments into the nature of electricity and magnetism. Understanding the relationship between the two forces and unifying them into a single force, called electromagnetism, proved to be a critical step. The unification of electricity and magnetism also established the existence of electromagnetic waves, the fundamental principle behind wireless technology.

Fascination and Curiosity

In the 1700s static electricity was a well-known phenomenon, and various devices were made to produce it. Electricity was poorly understood at first. Its main use was as an entertainment tool as it could create colorful sparks and move small objects. It was used in types of magic shows that were meant to delight crowds.

Over time the curious nature of electricity demanded an explanation, and a number of experimenters tried to find out. Where did electricity come from? Static electricity was observed to pass through people. Some animals were known to produce electric shocks. Therefore, was electricity intrinsic to life itself or were the living bodies a medium for carrying a fundamental force of nature?

In 1799, Alessandro Volta, an Italian physicist and chemist showed that electricity could be generated artificially. He created the first battery by piling up metal plates, separated by cards dipped in dilute acid, and attaching both ends to wires. Metals have a unique quality where at the atomic level the electrons in the outer shells can be shared. Under the right conditions the electrons can flow from one atom to another. This produces an electric current.

The unit for measuring electric potential is named in Volta’s honor (the volt). Up until Volta’s pile, as it was called, electricity could only last for an instant. Now it could be stored in a battery, which opened the door for electricity to do useful work. But the road of inventing electrical technologies would be long and winding. The knowledge of electricity was still in its infancy.

The Insights of Faraday and Maxwell

Michael Faraday was a self-educated scientist, who is famous for his experiments with electricity and magnetism. His work would lead to unlocking the secrets of the two mysterious forces. Faraday picked up the work of Danish physicist, Hans Christian Orsted. In 1820, Orsted accidentally discovered that a current carrying wire caused a nearby magnetic needle to move. In other words, an electric field created a magnetic field.

Knowing that an electric current had an effect on magnets at a close distance; Faraday wondered if the experiment could be reversed. Could magnets generate electricity? Faraday set out to explore the relationship further, and in 1831 he discovered that a changing magnetic field caused an electric current in a nearby wire. The key insight was that electricity was produced when the magnetic field changed as it interacted with the wire. A stationary magnetic field and a wire did not induce a current. Therefore, a third variable was needed – motion. The motion of a magnetic field in relation to a wire generated the electricity.

This principle, known as electromagnetic induction, is responsible for powering all electric motors and generators. Electric power is generated by a changing magnetic field and its interaction with a coil of wire. The coil multiplies the amount of power generated, but operates under the same principle as Faraday’s experiment with a single wire.

Three decades later a Scottish physicist by the name of James Clerk Maxwell put the finishing touch on the unification of electricity and magnetism. By the time Maxwell came along it was well-established that there existed a connection between the two forces. The telegraph had been invented, the first long-distance communication device, which operated on the principle of electromagnetism. Maxwell’s great achievement came in 1862; he devised 4 simple equations that represented all the interactions between electricity and magnetism.

The original concept of two distinct forces was united under one theoretical framework. Electromagnetism became known as one of the 4 fundamental forces of nature recognized by modern physics; the other 3 being, the strong nuclear force, weak nuclear force and gravity. In short, Faraday unified electricity and magnetism experimentally, and Maxwell unified them mathematically.

Fields, Waves and Light

With Maxwell’s equations came a new understanding of electromagnetism. Not only were the two forces unified, but the concepts of fields and waves would become extremely important. Modern physics would be transformed by the knowledge that energies could occupy regions of space and have noticeable effects. In This Explains Everything, physicist Lawrence Krauss writes:

“[Maxwell’s equations] established the physical reality of what was otherwise a figment of Faraday’s imagination: a field – that is, some quantity associated with every point in space and time.”

Maxwell realized that if a changing electric field created a magnetic field, and a changing magnetic field created an electric field, then the process would be continuous (a kind of chain reaction). The mutual interaction of electricity and magnetism would cause the field to oscillate. When an electromagnetic field oscillates it generates an electromagnetic wave, which has an independent existence and moves out from the source. Maxwell was able to calculate the speed at which electromagnetic waves propagate. It tuned out it was precisely the speed of light. Krauss writes about Maxwell’s conclusion:

“Thus he discovered that light is indeed a wave – but a wave of electric and magnetic fields that moves through space at a precise speed…”

Maxwell’s discovery of a constant speed of light was the starting point for Einstein’s revision of space and time – the theory of special relativity. A decade later Einstein formulated the theory of general relativity. It was then followed by quantum theory, and the age of modern physics was in full swing.

A World Beyond Imagination

The scientists and inventors of the 1700s and 1800s could not have imagined the modern world that resulted from their work. Electricity and information technology could not have been possible if not for a complete understanding of electromagnetism. It was the start of something big, and step by step new discoveries and inventions pushed the boundaries of progress. Many innovators took part in the quest. Our world has become brighter, smaller and faster.

I know I am dating myself; however, I grew up watching a black and white television. At first the TV only aired 2 channels, of which the signal was received by an antenna in the attic. There was no remote control back then, so we had to manually turn the dial to change the channel. In addition, someone had to walk up to the attic and turn the antenna around. Eventually, we upgraded by adding a second antenna (each pointing in a different direction) and running wires to a switch besides the TV. I guess that was progress back then. Nowadays people complain if the Wi-Fi is slow.

I am amazed at all the electronic gadgets we have today, and all they can do. They work on principles that take advantage of things we can’t even see. How can electrons moving through wires light our homes and power computers? How can waves traveling through space carry information that can be converted to video and audio? Plus, most of the time, the signal is perfectly clear. When I consider that it took 3 centuries of inventions to get to this point, I am not going to get upset over a slow WiFi; I am just grateful it works at all.

 

References: Edge Foundation Inc., This Explains Everything (New York: HarperCollins Publishers, 2013), 335, 336.

In Our Time: Science, Michael Faraday, Dec. 24, 2015.

In Our Time: Science, The Invention of Radio, July 3, 2013.

In Our Time: Science, Maxwell, Oct 1, 2003

Shock and Awe: The Story of Electricity — Jim Al-Khalili BBC Horizon, Published on May 26, 2015.


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.


 

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).


 

The Paradox of Wave-Particle Duality

blue light beam The wave-particle duality of light and other subatomic particles, such as electrons, is a central concept in quantum mechanics. The idea that light and elementary particles have both wave-like and particle-like properties is just one of a number of strange quantum realities. The quantum revolution, which began at the turn of the 20th century, has transformed our world from a technological standpoint. A century later the quantum laws underpin our modern technology. But scientists that were probing the atom in the early 1900s were simply trying to understand the nature of reality at the smallest scales. The challenges proved to be immense, mind-boggling and paradoxical. Wave-particle duality is one paradox that is still not completely understood.

The Photoelectric Effect

Albert Einstein is most famously known for the theories of special relativity, general relativity and the equation E=MC². However, in 1905 he won the Nobel Prize for his explanation of the photoelectric effect. Before Einstein, light was generally thought to behave like a wave, similar to a water wave. But there were some unsolved questions regarding properties of different colored light. Specifically, the ability of ultra-violet light to remove an electric charge from a metal plate (a phenomenon not observed with red light).

Photoelectric Effect

Photoelectric Effect

Einstein proposed that light was composed of packets of energy called quanta (later known as photon). These particles of light acted like miniature billiard balls, knocking the electrons off the metal plate. According to Einstein, the particles from the red light carried low energy, because red light has a low-frequency. Conversely, the higher frequency ultra-violet light contains higher energy particles, which were able to dislodge the electrons from the metal plate. With the analogy of the billiard balls, it was like the ultra-violet particles were heavier than the red light particles. Therefore, the heavy particles of light were able to knock off the electrons, while the lite particles could not.

Einstein’s explanation of the photoelectric effect showed that light was made up of individual particles. It opened the doorway to a new branch of physics. Although Einstein played a key role in the foundation of quantum physics, he never accepted the implications that the theory would eventually bear out. The idea that the quantum world was ruled by uncertainty, did not sit well with him. Einstein supported the classical view of physics, where precise predictions and conclusions could be made. Referring to the probabilistic foundation of quantum mechanics, Einstein said: “God does not play dice.”

 The Double-Slit Experiment

The discovery of the wave-particle duality of light was only the beginning of the paradoxes that would later emerge. A simple experiment, known as the double-slit experiment would overthrow any common sense notion of the quantum realm. The experiment worked as follows: An electron gun was set up to fire an electron beam through a barrier with two open slits. A full screen was placed a small distance behind the barrier. One would expect that the electrons that go through the slits would strike the background screen and produce two bands. However, the outcome showed not two, but a number of bands across the length of the screen; a striped pattern emerged.

Double-Slit Experiment

Double-slit Experiment

The electrons were behaving like a wave; the stripes were consistent with an interference pattern. This had already been observed in water waves. For instance, when two ripples in a pond meet they interfere with each other, causing the similar interference pattern that was observed with the electrons. Water is composed of individual molecules and together they combine to form a wave. Similarly, the electrons were exhibiting both wave-like and particle-like properties (this was also observed in light).

If this was not strange enough, the next step of the experiment would reveal a greater paradox. When the electron gun was allowed to fire one electron at a time, the screen in the back would eventually show the same striped pattern. How could single electrons produce an interference pattern? To point out how strange that was: it was like a single electron was passing through both slits at the same time, or like each electron was carrying information from the wave as it was passing through the slits.

Explaining the Impossible

Niels BohrDanish physicist Niels Bohr, one of the founders of quantum mechanics provided a possible explanation. It is known as the Copenhagen Interpretation. According to Bohr, the electrons that travel from the gun to the screen cannot be viewed as single point particles, but rather as a probability wave. In other words, an electron exists only as a spectrum of possibilities when it travels. It carries with it every possible path from the gun to the screen, including passing through the two slits at the same time. Only when it strikes the screen is the electron forced to take an exact position.

In this view, each electron will strike the screen at a different point, however, with a sufficient number of electrons the striped pattern will emerge on the screen. Whether the electrons are traveling in a continuous beam or as single travelers, the outcome will produce an interference pattern. Even if it is not completely understood, wave-particle duality is a fundamental property of the quantum world.

It is safe to say that Einstein and Bohr disagreed as to what is ultimately responsible for quantum uncertainty. For Bohr it was enough to apply a workable mathematical framework (based on probabilities), but for Einstein there must have been an undiscovered classical principle guiding the process. A century after Einstein and Bohr there is still no classical physical principle (one that agrees with common sense) that explains the uncertainty of quantum mechanics. However unsatisfying, it seems that Bohr’s explanation of the double-slit experiment is still as good as we have. Nevertheless, Bohr realized the gap between quantum mechanics and everyday experience, he said: “If quantum mechanics hasn’t profoundly shocked you, you haven’t understood it yet.”

In time, Bohr’s approach would lead to a revolution in technology. Even if exact outcomes cannot be known, physicists can calculate probabilities that will allow electronic devises to work. Similar to the double-slit experiment, even if the path of each individual electron cannot be known, the overall pattern can be predicted. Today, computers, mobile phones and GPS devices operate based on quantum mechanics.

 

References: The Secrets of Quantum Physics Episode 1 Einstein’s Nightmare BBC Documentary 2014. Published on Feb 28, 2015. https://www.youtube.com/watch?v=uV8oSgMhS54

Brainy Quote, 2001-2015. http://www.brainyquote.com/quotes/authors/n/niels_bohr.html

Brian Greene, The Fabric of the Cosmos.


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).


 

Ludwig Boltzmann: The Master of Disorder

BoltzmannThe principle in physics called entropy has a convoluted history. The genesis of the idea started in the 1800s with the industrial revolution and the advent of steam engines. Although steam power was producing an incredible amount of energy and transforming societies, the fundamental physical laws behind the process was largely unknown. The full story behind solving this question concludes with Austrian physicist, Ludwig Boltzmannand his view of entropy. His insights into the physical reality behind heat and energy were later applied to a much larger scheme, including the whole universe.

The Universe in a Coffee Cup

Why does a hot cup of coffee left on a table get colder over time? The answer to this simple question is at the heart of Boltzmann’s idea. The explanation is due to the behavior of atoms. Today, the existence of atoms is taken for granted, but back in the late 1800s many prominent scientists did not believe in atoms (including Ernst Mach, one of Boltzmann’s adversaries). No one had observed an atom, and it was thought that no one ever would. Nevertheless, Boltzmann peered deeper into the physical world than any of his contemporaries.

cup of coffeeLet’s get back to the hot cup of coffee. The heat from the coffee will disperse to the cup, the table and the surrounding air, until the temperature of the coffee is roughly equal to its environment. The same amount of energy still exists, but now covers a wider area. The flow of energy, left alone, will always flow from a hot source to a cold source. This natural flow of energy was the secret behind the steam engine, as the heat energy was converted to physical work. Boltzmann realized that this phenomenon of heat transferring and dispersing could be explained within the framework of atoms.

In the hot coffee, the atoms are tightly arranged and jostling about. The vibrations of the atoms are responsible for the heat. But as they move they contact the atoms of the cup, and transfer some of their energy. This continual process of bumping eventually distributes the heat energy to a much larger number of atoms. In the hot coffee the atoms are arranged in a unique way, but there are may possible arrangements in which the atoms can spread out. In the language of entropy, the system has moved from low entropy (an ordered state) to high entropy (a disordered state). The natural tendency for systems to move from order to disorder is now understood as a fundamental principle that underpins the entire universe. Loosely speaking, this describes the second law of thermodynamics.

 What is Order and Disorder?

disorderClassical physics, the method of scientific reasoning that held sway since Issac Newton, demanded that precise calculations were made. Physics was about discovering exactly how things moved and interacted. If atoms really existed, the sheer amount of them imposed an almost insurmountable problem. How could they ever be studied? Boltzmann took a different approach. Perhaps his greatest insight was that the motion of atoms could be described mathematically by using statistical probabilities. In addition to studying atoms, probabilities could be used to determine the amount of entropy in any system. This idea leads us to a definition of order and disorder:

  • Order means that there are very few configurations, if changed, which would go unnoticed.
  • Disorder means that there are many configurations, if changed, which would go unnoticed.

For example, take the analogy of a deck of playing cards. Dealt at random, there are few arrangements of cards that will line up in numerical order. Conversely, there are many arrangements of cards that will be mixed up. The reason is obvious. The probability is much higher for a disordered configuration than for an ordered configuration. Order is a special and unique condition, while disorder can come about in numerous ways. Therefore, we can conclude that high entropy (disorder) is a more natural state. We can still create order, but we need to intervene in some way. Still, any system left alone will move from order to disorder (or entropy will increase).

Statistical Reasoning

The entropy in a cup of coffee will tend to increase. Someone has to create the order by heating up the water and making the coffee. What would be the likelihood that the heat would naturally occur in the coffee? Of course we know that doesn’t make any sense. Thus by statistical reasoning, it makes perfect sense that disorder is more likely than order. Entropy, and in turn the second law of thermodynamics, is based on the probability of how any physical system will evolve. Eventually, everything dissolves, crumbles, decays, degrades and collapses.

We don’t need to look any further than our own homes, as it is a constant effort to maintain order (the special condition where items are neatly arranged). Disorder happens much more naturally, because there are many more ways in which the home can be disordered. Left unchecked, dirty dishes will accumulate, laundry will build up, and things will get scattered. The condition of the home’s structure will also degrade over time. This is all due to the principle of entropy.

A Story of Triumph and Tragedy

Boltzmann’s theories were highly controversial in his time; many prominent physicists rejected his ideas. And to make matters worse, he suffered from severe bouts of depression (probably due to undiagnosed bipolar disorder). On the positive side, he also went through periods of intense creativity. Aside from describing what entropy actually was, Boltzmann was able to put numbers to his theory. He devised a mathematical formula that could calculate the amount of disorder in a system.

His use of probabilities went against years of certainty behind the theories of classical physics. In the early 20th century, scientists would soon find his method useful in probing the atom. Probabilities would become a fundamental feature of quantum mechanics. The sad part to the story is that Boltzmann’s achievements would only be recognized after his death. In 1906, he committed suicide during one of his episodes of depression. Whether the final blow was delivered by his mental illness or the lack of recognition for his work is unclear. Nevertheless, his lasting legacy is engraved on his tombstone in Vienna: his equation for quantifying entropy, S = K log W.

 

References: Order and Disorder the ENERGY – HD Documentary, Published on June 24, 2014.


 

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