His formula for the relationship of mass and energy, E=mc[2], revolutionized the world of science. Undoubtedly one of the most influential physicists of all time, Albert Einstein (1879-1955) radically transformed our understanding of the universe. Perhaps best known for his theory of relativity, his contributions to physics are varied, unique, and still very relevant. He furthered our understanding of time, space, energy, and matter and contributed to the development of quantum physics. Practically all the modern physicists and astrophysicists are drawing from Einstein’s groundbreaking work, a never-ending testimony to this quintessential scientific genius.

Michio Kaku, a theoretical physicist and co-founder of string field theory, continues Einstein’s goal of a “theory of everything,” uniting the four fundamental forces of nature into one theory.

He hosts two weekly radio programs, “Science Fantastic” and “Explorations.” He also frequently appears on television, has written for popular science publications such as Discover, Wired, and New Scientist, has been featured in documentaries (“Me & Isaac Newton”), and hosted many of his own, including BBC’s series on Time.

Currently Professor of Theoretical Physics at the City University of New York, he is also the author of best-selling books, Parallel Worlds andHyperspace. His newest book, Physics of the Future: How Science Will Shape Human Destiny and Our Daily Lives by the Year 2100 was published in February 2012.

Simply Charly: What were Einstein’s major contributions to physics besides the theory of relativity?

Michio Kaku: In 1905, in addition to publishing relativity theory, Einstein made several other worthy breakthroughs. First, he experimentally proved the existence of atoms. We forget that in 1905, there were still scientists who scoffed at the theory of atoms. (In fact, the great physicist Ludwig Boltzmann was, in part, driven to suicide by the ridicule he faced from students of Ernst Mach, who believed that atoms did not exist and would never be seen experimentally. Sadly, Boltzmann died a year after the young Einstein proved the existence of atoms, showing that tiny molecular collisions called Brownian motion could explain why dust particles in water seemed to vibrate. Einstein could even calculate the size of the atom from this effect.)

Also in 1905, Einstein’s miracle year, he explained the photoelectric effect, how a light beam falling on metal would eject electrons and create a tiny current. Einstein introduced a particle of light, later called the photon, which forms the basis of the quantum theory of matter and light. Einstein is thus the godfather of the quantum theory, the other great theory of the 20th century. (The photoelectric effect and the photon are used today in solar cells, TV cameras, lasers, and modern electronics.)

SC: What is the difference between the special theory of relativity and the general theory?

MK: In 1905, Einstein proposed special relativity to explain the strange properties of light (e.g., that light travels at the same velocity no matter how fast you move, and that time slows down the faster you move.) This alone would have guaranteed him fame as one of the great physicists of all time. But Einstein was not satisfied. Special relativity could not explain gravitation or acceleration. From 1905 to 1915, he sought a general theory of relativity that would be more powerful than special relativity.

In 1915, he created general relativity, based on the idea that empty space could be curved. Anyone passing through curved space would have the illusion that a force was acting on them. In this way, Einstein explained the true nature of gravity. (For example, imagine ants walking on a crumpled sheet of paper. They are mysteriously tugged to the right and left, they claim, by an unseen force. But we know that there is no force acting on the ants. They are tugged in different directions because they are walking on curved space.)

Unlike special relativity, general relativity can explain large-scale astronomical phenomena, such as black holes, bending starlight, and the big bang theory.

SC: How does a physicist (or an astrophysicist) like yourself apply Einstein’s theory of relativity (and his other findings) to modern science?

MK: We apply Einstein’s theories every day to modern science. For example, Einstein predicted that when light passes by a star, the light beam bends (as if it were moving in glass). But if a light beam passes around distant galaxies, then we see a galaxy’s image distorted into the shape of a ring, called Einstein’s rings. Today, we see Einstein’s rings via our telescopes and use them to explore the universe. Also, astronomers have cataloged thousands of black holes in outer space. One lies at the very center of our Milky Way galaxy, weighing about 2 million suns. We can now show experimentally that these black holes obey the predictions made by Einstein decades ago. For example, Einstein said that space-time was like thick molasses that swirled around a black hole, dragging space along with it. We can now confirm this prediction by Einstein. Lastly, Einstein also introduced the concept of Bose-Einstein condensates. He showed that, when matter is cooled down to near absolute zero, atomic motion almost disappears, and atoms seem to coalesce into one gigantic superatom that vibrates in unison. Thus, tiny and strange quantum effects, which are usually too small to be seen in the lab, can be seen in a BE condensate. About 70 years or so after Einstein and Bose predicted the existence of this strange form of matter, it was finally found in the lab. In the future, perhaps laser beams made of atoms (and not light) and also quantum computers (and perhaps even invisibility) may be a byproduct of BE condensates.

SC: How do Einstein’s theories relate to your own work (string field theory, et al.)

MK: Einstein spent the last 30 years of his life (from 1925) searching for an even greater theory, which he called the unified field theory. It was to be his crowning achievement. He wanted a theory of everything, i.e., a theory which could unite all the fundamental forces of the universe into a single theory, which would allow him to “read the mind of God.”

Einstein failed in this mission, but perhaps he was onto something. Today, there are scores of physicists (myself included) who are trying to complete his dream of unifying all of physics into a single equation. The leading candidate is called string theory, which can unite Einstein’s relativity theory with the quantum theory. Remarkably, these two theories contain the sum total of all physics at the fundamental level.

For decades, anyone trying to unify relativity with the quantum theory was met with serious mathematical problems. Any naïve union of the two blows up in your face. Today, string theory is the only theory that can combine Einstein’s theory of gravity with the quantum theory and still yield finite, meaningful results.

SC: During one of your tv appearances you spoke about “dark energy,” a mysterious force that is causing the universe to fly apart faster and faster. You mentioned that Einstein was onto something called “cosmological constant,” but he thought he had made a mistake. Today this “mistake” has become an integral part of astrophysics. Can you elaborate on that?

MK: Just in the last five years, physicists have realized that there is a strange energy permeating all of space, called dark energy, which is causing the galaxies to accelerate away from each other. The universe, instead of slowing down (as was universally thought) is actually in a run-away mode, accelerating until perhaps we hit the Big Freeze. Temperatures will drop to near absolute zero, and the entire night sky will be totally black. (Dark energy or the energy hidden in empty space, was introduced by Einstein in 1916, but he later called it his greatest blunder. Strangely, Einstein’s blunder is perhaps the most important factor in determining the ultimate fate of the universe.)

At present, no one knows where this dark energy comes from. If one naively tries to calculate dark energy, one finds a huge mismatch. The theory is off by a factor of 10 raised to the 120 power! This is the largest mismatch in the history of science. Obviously, there are still huge gaps in our understanding of the universe if we cannot calculate dark energy (which makes up 73% of the matter and energy of universe. By contrast, the higher elements, which make our bodies, only make up .03% of the universe.)

SC: Which, if any, of his theories, have been refuted since his death and which are still being debated?

MK: Einstein’s most controversial belief was his criticism of the quantum theory. The quantum theory is the most successful theory of all time, but it is based on probabilities and chance. He did not believe that God played dice with the world.

Even today, physicists debate the philosophical questions raised by Einstein. For example, according to the quantum theory, a cat placed in a box is neither dead nor alive until you look at it. To describe it, you have to add the wave function describing a dead cat, with the wave function of a live cat. (Only when you open the box and make a measurement does the cat suddenly spring into existence as we know it.) So before you look at a cat in a box, it is neither dead nor alive, but exists in a netherworld as the sum of the two.

Philosophers used to ask, does a tree fall in a forest if there is no one there to listen to it? For centuries after Newton, scientists firmly believed that the universe existed independent of humans, and hence the tree either did or did not fall. But the quantum theory says otherwise. It says that until you actually see the tree, the tree exists in all possible quantum states (burnt, firewood, splinters, toothpicks, sawdust, a sapling, and an ordinary tree). Only when you look at it does the tree suddenly spring into existence.

Remarkably, Nobel Laureates have split on this question. Nobel laureate Eugene Wigner believed that observations determine existence, and observations require a conscious mind, and hence the existence of the universe meant that there was a cosmic consciousness permeating it. In some sense, he was offering this as a proof of the existence of God.

According to Niels Bohr, a founder of the quantum theory, “anyone who is not shocked by the quantum theory does not understand it.” For example, the quantum theory says that electrons can be two places at the same time (which sounds ridiculous, but actually stands at the foundation of all of chemistry.) When high school students learn chemistry, they draw “orbitals” or football-shaped clouds surrounding the atom, which binds two atoms together into a molecule. But the teacher rarely explains what this football is (because it might upset the students). The football-shaped cloud is actually the wave function of the electron being many places at the same time. The electron can bind two atoms into a molecule because the electron is many places at the same time surrounding both atoms, thereby connecting the two atoms. Hence, the fact that electrons can be two places at the same time is the reason why molecules hold together. Without the quantum theory, our atoms would dissolve immediately, and reality as we know it would disintegrate.

Einstein thought that this was silly, and he said so. Although the quantum theory is accurate to one part in 10 billion and makes possible all the miracles of lasers and modern electronics, it is based on a philosophical foundation of sand. Einstein once said that the more successful the quantum theory becomes, the sillier it looks.

Today, there is still no universal consensus on the questions raised by Einstein back in the 1920s concerning the quantum theory’s outrageous paradoxes. But one idea is gradually catching on, and this is “decoherence.”

For example, perhaps the cat splits into two cats or two universes. In one universe, the cat is dead. In the other universe, the cat is alive. So, at each juncture in the history of the universe, it constantly splits into two. The key is that we have “decohered” from these other universes, and hence can no longer communicate with these parallel universes. Nobel Laureate Steve Weinberg compares this to listening to a radio in your living room. You can hear many, many stations on your radio, so you know that there are many invisible radio waves permeating your living room. But your radio is tuned to only one frequency, and it has decohered from all the others. The radio frequency you are hearing no longer interacts with all the other radio frequencies, and you hear only one sound.

Likewise, in your living are the wave functions of alternate universes. There are the wave functions of dinosaurs, pirates, aliens, exploding stars, etc. in your living room. But you cannot interact with these parallel universes. Your universe no longer vibrates in unison with them, and hence has decoupled from them. (So, perhaps in one universe Elvis is still alive, but you can no longer interact with that universe.)

SC: While Einstein is best known for his theory of relativity, he was also a humanist and a philosopher. What are some of the lesser-known facts about him that might shed light on the kind of person he was outside of the science lab?

MK: I wrote a biography of Einstein, called Einstein’s Cosmos, and was amazed that he was able to keep his sanity and composure when constantly surrounded by the bitterness of chaos, hatred, and war. On the one hand, he had the adulation of millions of people (yet somehow never let it go to his head). Without a team of spin-doctors and press agents issuing press releases, Einstein almost single-handedly managed his public appearances and statements. On the other hand, the Nazis constantly denounced him in print, burned his books publicly, organized meetings to ridicule him, called relativity “Jewish physics,” hounded his friends into exile, and finally put a price on his head. (The Nazis put Einstein’s face on one of their magazines, with the subtitle “Not Yet Hanged.”) There was one failed assassination attempt on his life (by a deranged fan) and constant rumors that Nazi followers were eager to collect on the price on his head.

A weaker man would have buckled under this constant barrage of hate from the Nazis. But for Einstein, it only made him more determined to criticize the Nazis publicly, even though this was quite dangerous. Einstein, in fact, became the face of the anti-Nazi opposition within the scientific community.

SC: In your opinion, if he were alive today, what inventions/discoveries that have occurred since his death would he likely find the most amazing?

MK: Perhaps quantum teleportation, which is based on his work, would be the most amazing. As any fan of Star Trek knows, teleportation is the ability to disappear and have your atoms instantly appear somewhere else. In the lab, physicists have actually carried out the teleportation of individual photons and cesium atoms. (But it may take a decade to teleport the first molecule, and decades after that to teleport the first organic molecule, perhaps even a virus. Teleporting a human is way beyond our capabilities at present.)

Quantum teleportation actually uses a thought experiment that Einstein devised to try to destroy the quantum theory. It’s called the EPR experiment (after Einstein, Podolsky, and Rosen). Imagine two electrons or photons shooting out in opposite directions. Originally, they were vibrating in phase with each other. Even after they are separated, their wave functions are still vibrating in phase, so there is an invisible “umbilical cord” that still connects them. We say that these two electrons are in quantum coherence. For example, if one electron is vibrating in the up direction, then the other electron should be in the down direction (so the sum is zero, as before). Now let these two electrons travel for many light years. Then take a measurement of one electron. Let’s say that it spins down. You now know, FASTER THAN LIGHT, that the other electron is spinning up. Because nothing can travel faster than light, Einstein reasoned, all this is nonsense, and hence quantum coherence was ridiculous.

Actually, this experiment has now been done many times, and each time Einstein is wrong, and the quantum theory is correct. (But this does not violate relativity, since it is only random information that is traveling faster than light. You cannot send Morse code or a meaningful message using the EPR experiment. No useful information can be sent this way, so relativity is still not violated).

Today, physicists re-adapt the EPR experiment to create quantum teleportation. Objects that are vibrating in phase with each other are connected by quantum coherence, and we use this to teleport information about one atom into another, distant atom. (This means, however, that the original atom must be destroyed, so if Capt. Kirk teleports across space; his original body is destroyed in the process).

SC: What, in your view and based on your own work, still lies ahead in the way of amazing discoveries that are directly derived from Einstein’s theories?

MK: Recently, scientists have been building a series of fantastic instruments that may further our understanding of Einstein’s pioneering work. First of all, in 2008, the Large Hadron Collider will be turned on outside Geneva, Switzerland, the most powerful instrument of science ever built. It is 27 kilometers in circumference and will create beams of protons with trillions of electron volts in energy. These are energies not seen since the instant of the big bang itself. In fact, we call it a window on creation. We hope to find entirely new particles with this powerful atom smasher, including mini-black holes that are the size of sub-atomic particles. (They are so small that these black holes do not pose a danger. In fact, cosmic rays from outer space hit the earth all the time with more energy than the LHC, and nothing happens.)

We also hope to find new particles with the LHC, called sparticles, or super particles. These are higher vibrations of the string, which are so heavy that they have not been seen so far. Some of these sparticles have no charge and are, in fact, totally invisible. (These sparticles are the leading candidate for dark matter, an invisible form of matter which surrounds the galaxies, making up 23% of the matter-energy content of the universe. With dark matter and dark energy, we now realize that most of the universe is, in fact, dark, i.e., invisible, and that atoms like hydrogen and helium in the stars make up only 4% of the universe.)

Then, perhaps around 2015, NASA will send a new type of satellite into space to probe the heart of the big bang itself. LISA (Laser Interferometry Space Antenna) will detect gravity waves in space, i.e., shock waves of gravity caused by colliding black holes and even the instant of creation. (Gravity waves were predicted by Einstein decades ago.) It consists of three satellites, connected by laser beams, separated by 3 million miles. If a gravity wave still circulating the universe from the big bang hits LISA, it will jiggle the laser detectors, and we will measure its intensity and frequency.

LISA (or its successors such as the Big Bang Observer) might be sensitive enough to shed light on the pre-big bang universe. At present, no one knows where the big bang came from, or what happened before it. But string theory makes predictions as to what might have preceded the big bang, and can predict the radiation emitted from these pre-big bang scenarios. Therefore, scientists hope that by analyzing gravity waves from the big bang, we will be able to compare this radiation with the predictions made by these pre-big-bang theories. In this way, we might be able to determine which model is correct, and therefore what most likely happened before the big bang. (One serious possibility is that our universe is a bubble floating among billions of other bubble/universes in 11-dimensional hyperspace. Occasionally, these bubble/universes collide, split in half, sprout baby bubbles, or pop into existence. Einstein gave us the fourth dimension. Now, physicists are going beyond four dimensions and investigating 11-dimensional space-time.)

SC: For students (and people in general) who are not Einsteins, how can his concepts be made easier to understand?

MK: One of my favorite Einstein quotes is that unless a theory can be explained to a child, the theory is probably useless. By this, he meant that the essence of a theory has to be a simple, elegant physical picture or principle that even children can grasp. All too often, physicists get lost in a thicket of mathematics that eventually leads to nowhere. The guiding principle must always be pictorial and simple.

For example, the essence of special relativity can be summarized in one picture. When he was 16-years-old, he visualized racing alongside a light beam. Since light is a wave, the light beam should appear frozen as you moved neck-and-neck with the beam. But no one had ever seen a frozen wave before, and hence Einstein as a boy was led to believe that it was impossible to outrace a light beam. In fact, he came to a radical conclusion that light always travels at the same speed, no matter how fast you moved.

Similarly, general relativity can be explained by pictures that children can understand. Imagine a large funnel, and then throw a marble along the surface. The marble will circulate around the center of the funnel, because the surface is curved. Now replace the marble with the earth, replace the center of the funnel with the sun, and we see that the earth orbits around the sun not because gravity pulls on the earth, but because the space around the sun pushes the earth. In other words, “gravity does not pull, space pushes.” This, in one phrase, is the essence of general relativity.

SUGGESTED READING