Space and Time Warps - Stephen Hawking
People think it's an interesting coincidence that Stephen Hawking died on March 14, Albert Einstein was born on March 14th & died aged I first met Stephen Hawking when we were students. .. Stephen insisted that he was not another Albert Einstein; none the less, few, if any. Image: File image of Stephen Hawking addressing a public meeting in . He also went on to receive the Albert Einstein Award and Hughes.
He turned 21 a week later, and shortly after he entered the hospital for two weeks of tests to discover what was wrong with him. He was then diagnosed with amyotrophic lateral sclerosis ALSalso known as Lou Gehrig's disease, which is a neurological disease that causes patients to lose control of their voluntary muscles.
He was told he'd probably only have a few years to live, the report says. Hawking remembers being shocked and wondering why this happened to him. However, seeing a boy dying of leukemia in the hospital made him realize that there were others worse off than him. Hawking became more optimistic and started dating Jane.
They were soon engaged, and he cites their engagement as giving him "something to live for," the report adds. Hawking helped create the boundless universe theory Photograph: One of Hawking's major achievements which he shares with Jim Hartle was to come up with the theory that the universe has no boundaries in Inthe effort to understand the nature and shape of the universe, Hawking and Hartle combined the concepts of quantum mechanics the study of the behaviour of microscopic particles with general relativity Einstein's theories about gravity and how mass curves space to show that the universe is a contained entity and yet has no boundaries, the report notes.
Hawking lost a bet on black holes! A NASA illustration of a growing supermassive black hole. Reuters InHawking admitted he had been wrong and conceded a bet he made in with a fellow scientist about black holes. Hawking had said at the time that information is lost in the black hole that eventually evaporates. The problem was that this idea that information is lost conflicted with the rules of quantum mechanics, creating what Hawking called an "information paradox. Inhe made a bet with Hawking saying that information can escape from them, thus not breaking the laws of quantum mechanics, the report states.
Hawking is such a good sport that he can admit when he's wrong -- which he did in While giving a lecture at a scientific conference, he said that because black holes have more than one "topology," and when one measures all the information released from all topologies, information isn't lost, the report adds.
Hawking has won numerous awards and distinctions Image: Reuters In his long career in physics, Hawking had racked up an incredibly impressive array of awards and distinctions. Hawking had so well established himself in the academic world by that he attained the post of Lucasian Professor of Mathematics at the University of Cambridge in England -- a position he would keep for the next 30 years.
The chair dates all the way back toand the second person to hold it was none other than Sir Isaac Newton, the report notes.
In the s, he was invested as a Commander of the British Empire, which is a rank in the UK just under being knighted. He also became a Companion of Honour, which is another distinction given in recognition of national service.
There can no more than 65 members of the order at one time. All the while, Hawking attained at least 12 honorary degrees. Hawking also authored children's books Image: The cover of George's Secret Key to the Universe. He begins to befriend neighbours, one of whom is a physicist with a computer. This turns out to be most powerful computer in the world, which offers portals to see and enter into outer space, the report notes.
The book was written to be the first of a trilogy that would continue George's adventures. The next one in the series came out in and is called 'George's Cosmic Treasure Hunt', the report adds.
Hawking believed in the possibility of alien life Photograph: Reuters During NASA's 50th anniversary celebration inHawking was invited to speak, and he mentioned his thoughts on the subject of possibility if alien life. He expressed that, given the vastness of the universe, there very well could be primitive alien life out there, and it is possible, other intelligent life. He went on the say that humans should be wary of exposure to aliens because alien life will probably not be DNA-based, and we would not have resistance to diseases, the report points out.
Hawking's 'zero gravity' flight to save human race Image: Picture of Stephen Hawking taking a 'zero gravity' float without his wheelchair. Reuters InHawking got to take the ride of a lifetime. He was able to experience zero-gravity and float out of his wheelchair thanks to Zero Gravity Corp.
The service involves an airplane ride in which sharp ascent and descent allows passengers to experience weightlessness in flight for several rounds, each about seconds long, the report notes. Hawking, free from his wheelchair for the first time in four decades, was even able to perform gymnastic flips. The answer is given in the following Limerick. There was a young lady of Wight, Who traveled much faster than light, She departed one day, In a relative way, And arrived on the previous night.
So all we need for time travel, is a space ship that will go faster than light. Unfortunately, in the same paper, Einstein showed that the rocket power needed to accelerate a space ship, got greater and greater, the nearer it got to the speed of light. So it would take an infinite amount of power, to accelerate past the speed of light. Einstein's paper of seemed to rule out time travel into the past. It also indicated that space travel to other stars, was going to be a very slow and tedious business.
If one couldn't go faster than light, the round trip to the nearest star, would take at least eight years, and to the center of the galaxy, at least eighty thousand years. If the space ship went very near the speed of light, it might seem to the people on board, that the trip to the galactic center had taken only a few years.
But that wouldn't be much consolation, if everyone you had known was dead and forgotten thousands of years ago, when you got back. That wouldn't be much good for space Westerns. So writers of science fiction, had to look for ways to get round this difficulty. In his paper, Einstein showed that the effects of gravity could be described, by supposing that space-time was warped or distorted, by the matter and energy in it.
We can actually observe this warping of space-time, produced by the mass of the Sun, in the slight bending of light or radio waves, passing close to the Sun.
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This causes the apparent position of the star or radio source, to shift slightly, when the Sun is between the Earth and the source. The shift is very small, about a thousandth of a degree, equivalent to a movement of an inch, at a distance of a mile. Nevertheless, it can be measured with great accuracy, and it agrees with the predictions of General Relativity. We have experimental evidence, that space and time are warped. The amount of warping in our neighbourhood, is very small, because all the gravitational fields in the solar system, are weak.
However, we know that very strong fields can occur, for example in the Big Bang, or in black holes. So, can space and time be warped enough, to meet the demands from science fiction, for things like hyper space drives, wormholes, or time travel. At first sight, all these seem possible.
For example, inKurt Goedel found a solution of the field equations of General Relativity, which represents a universe in which all the matter was rotating. In this universe, it would be possible to go off in a space ship, and come back before you set out.
Goedel was at the Institute of Advanced Study, in Princeton, where Einstein also spent his last years. He was more famous for proving you couldn't prove everything that is true, even in such an apparently simple subject as arithmetic.
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But what he proved about General Relativity allowing time travel really upset Einstein, who had thought it wouldn't be possible. We now know that Goedel's solution couldn't represent the universe in which we live, because it was not expanding. It also had a fairly large value for a quantity called the cosmological constant, which is generally believed to be zero. However, other apparently more reasonable solutions that allow time travel, have since been found. A particularly interesting one contains two cosmic strings, moving past each other at a speed very near to, but slightly less than, the speed of light.
Cosmic strings are a remarkable idea of theoretical physics, which science fiction writers don't really seem to have caught on to. As their name suggests, they are like string, in that they have length, but a tiny cross section. Actually, they are more like rubber bands, because they are under enormous tension, something like a hundred billion billion billion tons.
A cosmic string attached to the Sun would accelerate it naught to sixty, in a thirtieth of a second. Cosmic strings may sound far-fetched, and pure science fiction, but there are good scientific reasons to believed they could have formed in the very early universe, shortly after the Big Bang.
Because they are under such great tension, one might have expected them to accelerate to almost the speed of light. What both the Goedel universe, and the fast moving cosmic string space-time have in common, is that they start out so distorted and curved, that travel into the past, was always possible.
God might have created such a warped universe, but we have no reason to think that He did. All the evidence is, that the universe started out in the Big Bang, without the kind of warping needed, to allow travel into the past. Since we can't change the way the universe began, the question of whether time travel is possible, is one of whether we can subsequently make space-time so warped, that one can go back to the past.
I think this is an important subject for research, but one has to be careful not to be labeled a crank. If one made a research grant application to work on time travel, it would be dismissed immediately.
No government agency could afford to be seen to be spending public money, on anything as way out as time travel. Instead, one has to use technical terms, like closed time like curves, which are code for time travel. Although this lecture is partly about time travel, I felt I had to give it the scientifically more respectable title, Space and Time warps.
Yet, it is a very serious question. Since General Relativity can permit time travel, does it allow it in our universe? And if not, why not. Closely related to time travel, is the ability to travel rapidly from one position in space, to another. As I said earlier, Einstein showed that it would take an infinite amount of rocket power, to accelerate a space ship to beyond the speed of light. So the only way to get from one side of the galaxy to the other, in a reasonable time, would seem to be if we could warp space-time so much, that we created a little tube or wormhole.
This could connect the two sides of the galaxy, and act as a short cut, to get from one to the other and back while your friends were still alive. Such wormholes have been seriously suggested, as being within the capabilities of a future civilization. But if you can travel from one side of the galaxy, to the other, in a week or two, you could go back through another wormhole, and arrive back before you set out.
You could even manage to travel back in time with a single wormhole, if its two ends were moving relative to each other. One can show that to create a wormhole, one needs to warp space-time in the opposite way, to that in which normal matter warps it. Ordinary matter curves space-time back on itself, like the surface of the Earth. However, to create a wormhole, one needs matter that warps space-time in the opposite way, like the surface of a saddle. The same is true of any other way of warping space-time to allow travel to the past, if the universe didn't begin so warped, that it allowed time travel.
What one would need, would be matter with negative mass, and negative energy density, to make space-time warp in the way required. Energy is rather like money.
If you have a positive bank balance, you can distribute it in various ways. But according to the classical laws that were believed until quite recently, you weren't allowed to have an energy overdraft. So these classical laws would have ruled out us being able to warp the universe, in the way required to allow time travel. However, the classical laws were overthrown by Quantum Theory, which is the other great revolution in our picture of the universe, apart from General Relativity.
Quantum Theory is more relaxed, and allows you to have an overdraft on one or two accounts. If only the banks were as accommodating. In other words, Quantum Theory allows the energy density to be negative in some places, provided it is positive in others.
The reason Quantum Theory can allow the energy density to be negative, is that it is based on the Uncertainty Principle. This says that certain quantities, like the position and speed of a particle, can't both have well defined values.
The more accurately the position of a particle is defined, the greater is the uncertainty in its speed, and vice versa. The uncertainty principle also applies to fields, like the electro-magnetic field, or the gravitational field. It implies that these fields can't be exactly zeroed, even in what we think of as empty space.
For if they were exactly zero, their values would have both a well-defined position at zero, and a well-defined speed, which was also zero.
This would be a violation of the uncertainty principle. Instead, the fields would have to have a certain minimum amount of fluctuations. One can interpret these so called vacuum fluctuations, as pairs of particles and anti particles, that suddenly appear together, move apart, and then come back together again, and annihilate each other. These particle anti particle pairs, are said to be virtual, because one can not measure them directly with a particle detector.
However, one can observe their effects indirectly. One way of doing this, is by what is called the Casimir effect. One has two parallel metal plates, a short distance apart. The plates act like mirrors for the virtual particles and anti particles. This means that the region between the plates, is a bit like an organ pipe, and will only admit light waves of certain resonant frequencies. The result is that there are slightly fewer vacuum fluctuations, or virtual particles, between the plates, than outside them, where vacuum fluctuations can have any wavelength.
The reduction in the number of virtual particles between the plates means that they don't hit the plates so often, and thus don't exert as much pressure on the plates, as the virtual particles outside.
There is thus a slight force pushing the plates together. This force has been measured experimentally. So virtual particles actually exist, and produce real effects.
Because there are fewer virtual particles, or vacuum fluctuations, between the plates, they have a lower energy density, than in the region outside. But the energy density of empty space far away from the plates, must be zero. Otherwise it would warp space-time, and the universe wouldn't be nearly flat.
So the energy density in the region between the plates, must be negative. We thus have experimental evidence from the bending of light, that space-time is curved, and confirmation from the Casimir effect, that we can warp it in the negative direction. So it might seem possible, that as we advance in science and technology, we might be able to construct a wormhole, or warp space and time in some other way, so as to be able to travel into our past.
If this were the case, it would raise a whole host of questions and problems. One of these is, if sometime in the future, we learn to travel in time, why hasn't someone come back from the future, to tell us how to do it.
Even if there were sound reasons for keeping us in ignorance, human nature being what it is, it is difficult to believe that someone wouldn't show off, and tell us poor benighted peasants, the secret of time travel. Of course, some people would claim that we have been visited from the future. They would say that UFO's come from the future, and that governments are engaged in a gigantic conspiracy to cover them up, and keep for themselves, the scientific knowledge that these visitors bring.
All I can say is, that if governments were hiding something, they are doing a pretty poor job, of extracting useful information from the aliens. I'm pretty skeptical of conspiracy theories, believing the cock up theory is more likely. The reports of sightings of UFO's can't all be caused by extra terrestrials, because they are mutually contradictory. But once you admit that some are mistakes, or hallucinations, isn't it more probable that they all are, than that we are being visited by people from the future, or the other side of the galaxy?
If they really want to colonize the Earth, or warn us of some danger, they are being pretty ineffective. A possible way to reconcile time travel, with the fact that we don't seem to have had any visitors from the future, would be to say that it can occur only in the future. In this view, one would say space-time in our past was fixed, because we have observed it, and seen that it is not warped enough, to allow travel into the past.
On the other hand, the future is open. So we might be able to warp it enough, to allow time travel. But because we can warp space-time only in the future, we wouldn't be able to travel back to the present time, or earlier.