Michio Kaku (born January 24, 1947) is an American theoretical physicist, futurist, and popularizer of science (science communicator). He is a professor of theoretical physics in the City College of New York and CUNY Graduate Center. Kaku has written several books about physics and related topics, has made frequent appearances on radio, television, and film, and writes online blogs and articles. He has written four New York Times best sellers: Physics of the Impossible(2008), Physics of the Future (2011), The Future of the Mind (2014). Kaku has hosted several TV specials for the BBC, the Discovery Channel, the History Channel, and the Science Channel.
If you don’t follow his Twitter feed you really should. He has been posing scientific riddles the past few months and then answering them a week later. If you’re like me you can’t wait a week to find out the answer. Here are some of his most interesting answers:
If time travel is possible, then how can you become your own mother, father, son, and daughter, all at once?
1. an orphan (Jane) has a sex change operation and turn into Jim
2. Jim goes back in time, meets Jane, and has a baby
3. They go back in time and drop the baby at an orphanage, who then becomes Jane.
If time travel is possible, then physics allows you to become your own mother, father, son, daughter. You are your own family tree. But the normal laws of genetics forbids this. Question: why?
If time travel is possible, then genetically can you be your own mother, father, son, and daughter? No. Females typically have XX chromosomes, while males have XY. A time traveler would have to change their sex chromosomes, which today is impossible.
Two twins are in two separate but identical rockets, on a collision course. Their telescopes tell them that the other twin in aging slower than normal (as predicted by Einstein). This means you have two twins, each younger than the other!! How is that possible??
If two twins are rocketing towards each other in a collision course, and each has a telescope and sees the other twin aging slower, then how can two people each be younger than the other when they meet? When the twins meet, they come to a halt, and each sees the other aging rapidly, as light catches up to them, until they both have the same age. “Younger” and “shorter” has no meaning in relativity unless you bring the twins together in the SAME frame.
Time travel is full of paradoxes e.g. going back in time and killing yourself as a child. (How can you exist if you just committed suicide in past?) But the quantum theory gives us the simplest solution to these paradoxes, in just one sentence. What is that sentence?
In the Many Worlds theory, the time line splits or forks, hence you wind up in a parallel universe when you go back in time, with NO paradoxes at all.
If we take Einstein’s general theory of relativity, and then set the speed of light to be infinite, then what happens to the equations of Einstein??
The answer is: Einstein’s equations reduce to Newton’s laws. So in a Newtonian universe, all messages are sent infinitely fast (which is incorrect.)
With a quick glance at Newton’s equations, how can you tell immediately that it violates relativity? With a quick glance at Einstein’s equations, how can you tell that it violates the quantum theory??
The answer is: Einstein’s equations reduce to Newton’s laws. So in a Newtonian universe, all messages are sent infinitely fast (which is incorrect.)
What happens if you have dark matter in your hand and let go?
Dark matter will penetrate your hand and fall through the floor, through the center of the earth, reach the other side of the earth. It will then oscillate back and forth through the earth, forever.
In the final scenes of the movie Interstellar, what was Matthew McConaughey doing, floating in some kind of prison? What scientific principle was being explored?
With just a glance, how do you tell that Newton’s laws violate relativity, and relativity violates the quantum theory? Newton’s equation do not mention c, light speed, and Einstein’s theory makes no mention of h, Planck’s constant.
What might alien intelligent life look like?
I don’t know. But own evolution favored 3 things: a) some form of stereo eyesight b) some form of thumb or grasping instrument c) language. Even on earth, among animals only humans have developed all three.
How to verify string theory?
Critics claim that string theory is untestable. But there are number of experiments to test it. If dark matter particles are create by the LHS, or found in detectors, they might be photinos, the super particle of the photon predicted by string theory.
What was Matthew McConaughey doing, floating in a cell at the end of Interstellar?
He was floating in the hyperspace predicted by string theory. Since 10 and 11 dimensions cannot be described on film, the producers had him floating in a 4D hypercube.
Can you prove the existence of God?
Probably not. Science is based on evidence which is testable, reproducible, and falsifiable. So God is outside the usual boundary of science. Also, it is impossible to disprove a negative, so you cannot disprove the existence of God, either. Similarly, you cannot definitively prove the non-existence of unicorns. So I am not an atheist. I personally find much wisdom in Einstein’s belief in the God of Spinoza, a God of beauty, simplicity, elegance, and truth, when the universe might have been random, ugly, and chaotic.
My colleague, the late Stephen Hawking, did not believe in God because there was no time in which to create the universe right after the big bang. But string theory actually takes you before the big bang, to the multiverse. So the big bang is the not the beginning of time. String theory leaves open the possibility that our bubble/universe collided or fissioned into other universes, as in a bubble bath, so there was a multiverse of universes before our universe was born. This idea might even be testable. So the big bang was just the collision of two universes, or the fissioning of a universe into a baby universe. This concept fits into the inflationary universe theory, which all the data and is the leading theory of the big bang itself. So time did not begin with the big bang.
If the universe is expanding, then what is it expanding into?
Personally, I believe the universe is expanding into hyperspace, ie. into 11 dimension, according to string theory, like a floating bubble in a much larger arena. However, the standard answer is that it’s just the distance between galaxies that is increasing, so the universe isn’t expanding into anything at all (like uniformly stretching a two dimensional sheet of rubber, which only expands in the same two dimensions, not three).
If nothing can escape the grip of a black hole, then why doesn’t it suck in everything, including the earth?
Far from the event horizon, the gravity around a black hole is Newtonian, i.e. diminishes like the inverse square of the distance. Hence, the earth orbits safely around the black hole at the center of the galaxy. If an object gets too close to the event horizon of a black hole, then it might get sucked in. But farther away from the event horizon, the gravity field looks normal, so stars orbit safely around it.
Mars once had great rivers, lakes, perhaps even oceans. But they all disappeared billions of years ago. Why?
The leading theory is that Mars has a very weak magnetic field, so cannot protect itself from the harsh solar wind, which gradually dissipated the atmosphere of Mars. This caused the oceans to boil and evaporate into space.
The electromagnetic spectrum is huge, ranging from radio, TV to X rays and gamma rays, yet our eyes can only see the tiniest sliver of this huge spectrum, visible light. Why?
In general, the size of an antenna is roughly the size of the wavelength. Our antennas are the cells in our retina, which are roughly the size of the wavelength of light, not radio or gamma rays. So if the cells of our eyes were many feet across, we could see radio. In other words, our eyes would look like a radio antenna. So we can only see EM waves the size of our cells, e.g. visible light… so if our cells and receptors were the size of a radio telescope, perhaps we could see the afterglow of the Big Bang itself filling up the sky.
The brain is not a digital computer. It has no operating system, no Windows, no CPU, no Pentium chip, no programming, no algorithms, no subroutines. When what is it?
It is a sophisticated learning machine, a very advanced neural network. After a making a mistake, the wiring of the brain actually changes to get closer to the answer.
Where does Einstein’s theory of gravity completely break down? (Einstein himself knew this, that is he was searching for the theory of everything, the unified field theory.)
At the center of a black hole, and the instant of the Big Bang. If r is the effective size of a singularity, then gravity behaves like 1/r, which is 1/0, which is nonsense. Einstein himself knew this, and that is why he was searching for a unified field theory. Also, that’s why he invented wormholes in 1935, to try to eliminate the 1/r problem (since wormholes are not singular). But so far, only string theory can eliminate these 1/r problems.
A star’s gravity can effortlessly squeeze hydrogen until it ignites. But fusion with magnetic fields on the earth is notoriously difficult. Why is that? What is the fundamental difference between gravity and magnetism??
Magnetism is based on dipoles (north and south poles) while gravity is based on monopoles of matter. Hence, stars can easily spherically contract under gravity, causing them to ignite. But dipoles are difficult. To use magnetism to squeeze hydrogen, you need to shape the magnets like a doughnut, with the gas inside. Doughnuts are much more difficult to squeeze than spheres. Hence we don’t have fusion reactors on the earth today.
Everyone says that every snowflake is unique. But how do we know that? No one examines every snowflake with a microscope. So how do we prove that every snow flake is different?
As a snow flake falls, the growth of its crystal arms changes with varying temperature, pressure, moisture. Since the path of every snowflake is unique, so therefore every snowflake is also unique.
What is my favorite science fiction novel?
Hands down, it would be the Foundation Trilogy by Asimov. As a child, it forced me to think of where humanity might be 50,000 years into the future. (Elon Musk also read that book as a child, I found out.)
Why did I become a physicist?
When I was 8, the newspapers said that a great scientist had died, and they published a picture of his desk, with his greatest, unfinished work. I asked myself: what could be so hard, that this great physicist could not finish??? I went to the library, and found out that this man was called Albert Einstein. And that unfinished book was the Unified Field Theory, the theory of everything. I decided that I wanted to try to help finish that book, to find this fabled theory unifying all the forces of nature.
What is my favorite science fiction movie?
Besides Forbidden Planet, it would be the old Flash Gordon series. As a child, it opened my eyes to the possibility of alien life in the universe (another admirer is George Lucas, upon which he based Star Wars.)
In the animal kingdom, very, very few animals snore. We humans are an exception. What other familiar animal snores, and why?
Very few animals snore. Over millions of years, our snout, jaw, began to get smaller, compressing our nasal cavity, causing snoring. Breeding of dogs (which were once gray wolves) also compressed the face of bull dogs and other animals, hence they snore.
Where does the most aging take place in a car? By analogy, then where does the most aging take place in the human body? Why does the answer to this hold an important clue to finding immortality?
In a car, its mainly in the engine, where you have oxidation and moving parts. In the cell, it is the mitochondria, the engine of the cells. That is also where mutations are concentrated. Aging, in some sense, is the buildup of errors in our cells. Since these mutations are concentrated in certain areas, perhaps one day science my repair the damage in these areas, such as the mitochondria, and hence reverse the effects of aging.
This tweet is written in English, rather than German, partly because the Nazis failed to build an atomic bomb. They failed, in part, because they did not know the value of one number. What is that number?
In part, it is because they did not know critical mass (about 20 pounds), the amount of enriched uranium necessary to build an a-bomb. One reason they did not know this is because all the top physicists fled the Nazis
Some things can go faster than light, like when you sweep the night sky with a flash light. The image went across millions of light years. But why doesn’t this violate Einstein’s special relativity theory?
If you sweep the night sky with a flashlight, does image of the beam eventually go faster than light? Yes. But no material object or information went faster than light, so relativity is not violated. The image is immaterial and hence can go faster than light.
If two electrons are vibrating coherently in unison, and are separated, then jiggling one electron instantly communicates information, faster than light. This is entanglement. But why doesn’t this violate Einstein’s theory of relativity?
Yes, but no net quantum information (e.g. Morse code) can travel this way. So Einstein was only partly incorrect. So Einstein was only partially right. Material objects (atoms, photons) and net information (e.g. Morse code) cannot go faster than light. But immaterial things can break the light barrier (e.g. the expansion of the universe in the big bang). So Einstein still has the last laugh. So this means that quantum entanglement cannot be used as the “subspace communicator” in Star Trek, allowing the Enterprise to communicate with Star Fleet Command instantly across the galaxy. But that still leaves open the possibility of wormholes. Going through a wormhole, you may theoretically zap across the galaxy, but your speedometer on your rocket always says you are going slower than light speed. Hence, special relativity is not violated locally going through a wormhole.
Why do hurricanes spin counterclockwise in the northern hemisphere? If you pull the plug in the sink, does the water drain counterclockwise as well?
As hot air rises, the earth spins beneath it slightly, causing it to swirl counterclockwise. This is the Coriolis force. In your sink, the slightest disturbance can nullify this weak force.
If you swing around a long steel rod from one end, and if the rod is long enough, will the end of the rod eventually exceed the speed of light?
If you spin a very long steel rod around you, will the end eventually go faster than light? No. If you jerk the rod, a shock wave travels along the rod, causing the shape to deform. If you jerk the rod so that it spins around you, the rod turns into a spiral. Since the shock wave travels much less than the speed of light (the shock wave actually moves comparable to the speed of sound) the rod never comes close to the speed of light.
Why is the sky blue, and the sunset red? Why is the night sky black, and not white? What is the color of the sky on Mars?
When you look at the sky, you are looking away from the sun at scattered light, and blue light scatters the most. At sunset, you are looking directly at the sun, through much of the atmosphere, and red light scatters the least. If the universe is uniform and infinite, then the sky should be on fire, since there is a star at every point you look. But since you look into the past when looking at distant stars, you eventually reach a cut-off, the big bang. So the sky is black because there was a beginning! So the night sky is black because there was a Beginning, a genesis to the universe. (I think about this when I take a shower.) The first person to solve this puzzle (Olber’s Paradox) was, of all people, Edgar Allen Poe, an amateur astronomer.
What is the color of the Martian sky? Its is pink. That is because it is full of small particles of dust, which contains rust. So Mars is the rusty planet.
Black holes absorb everything that gets too close. That’s why they are black. But this violates the quantum principle. Why?
Black holes cannot really be black. The quantum principle says that perfect Blackness violates the Uncertainty Principle, since you cannot have an object which emits absolutely no radiation. Hence black holes must be gray (which was Hawking’s contribution).
Why are stars and planets all round? And why are asteroids shaped like a potato?
Gravity is attractive, and evenly symmetrically compresses gases into a sphere. (A sphere has the least gravitational potential energy.) But small asteroids have little gravity, and hence they are shaped like a potato.
Where do Newton’s laws break down, requiring Einstein’s relativity? Where does relativity break down, requiring quantum gravity?
Newton’s laws are fine, except near the speed of light, or near large gravitational fields. Relativity breaks down at the center of a black hole, or at the big bang. Relativity is useless at the Planck energy (a quadrillion times greater than the LHC.)
When Einstein was 16 years old, he asked himself a fateful question: what happens if you can race along side a light beam? He changed human history when he finally found the answer ten years later. What is the answer?
When Einstein was 16, he dreamed of running along side alight beam, thinking that the wave would be stationary. But as a kid, he knew that stationary waves were never seen, so he concluded you could never race a light beam. Something was very wrong. When Einstein was in college, he finally learned Maxwell’s equations for light, and found the answer: light always travels at the same velocity, no matter how you measure it.. From this, he then showed that light speed was the ultimate velocity, so you could never outrace light.
If you are in a rocket ship traveling just below the speed of light, and then you fire a gun and turn on a flashlight, how fast is the light traveling? How fast is the bullet traveling?
If you measure the speed of a light beam on the earth, or inside a rocket ship traveling near light speed, light travels at the SAME velocity. If someone fires a gun inside the rocket ship, from the earth the velocity of the bullet does NOT exceed light speed. Time slows down inside the rocket ship. So someone inside the rocket ship measures the bullet’s speed as normal, as if the rocket were at rest. So the bullet NEVER exceeds light speed, either measured from the earth or inside the rocket.
How do refrigerators and air conditioners get cold? (Hint: it’s the same principle behind how stars get hot, before fusion takes place).
When a gas is squeezed, the energy of compression turn into heat, as in a star. When gases expand, they get absorb energy, and get cold, and that is how refrigerators work.
Biggest atom smasher in the world?
The Large Hadron Collider, the biggest atom smasher on earth, is down for the next 2 years. Then it will be at full power. Hopefully, it will find the photino, predicted by string theory, which may make up the dark matter filling up the universe. There is also a lesson here. In the 1990s, US physicists wanted to build the Supercollider (much bigger than the LHC) outside Dallas, TX. But Congress canceled it, so the US lost the lead in high energy physics. Lesson: we physicists have to learn how to engage the public, or else the public won’t fund us. The history of the Supercollider is a sad one. First, Congress gives us a billion dollars to dig the hole for the Supercollider. Then Congress cancels it, and gives a second billion dollars to fill up the hole. 2 billion dollars to dig and fill up a hole! That’s the Congress!
In the laboratory, scientists can artificially induce the feeling of being “out of body,” and also the near-death sensation of seeing the “light at the end of the tunnel.” How is this done? (Hint: see my book, The Future of the Mind).
The “light at the end of a tunnel” can be duplicated by putting pilots in an ultracentrifuge. As blood drains from their head, the outer rim of their retina loses blood, so you only see the center of the retina, so you see a light at the end of the tunnel. The “light at the end of the tunnel,” caused by a drop in blood pressure, can also happen in an accident, so therefore people think they have died and seen heaven. “Out of body experiences” can also be duplicated by electrically stimulating certain regions of the brain. By stimulating the boundary between two areas of the brain, it gets confused. To make sense of these contradictory signals, the brain interprets this as being outside the body. This effect can simply be created by an electrical probe to the brain.See The Future of the Mind.