How to Build a Time Machine: The Real Science of Time Travel

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Now it's easy to show that this is true in the first three dimensions. But trust me, it's also true of the fourth dimension. There are tiny crevices, wrinkles and voids in time. Down at the smallest of scales, smaller even than molecules, smaller than atoms, we get to a place called the quantum foam. This is where wormholes exist. Tiny tunnels or shortcuts through space and time constantly form, disappear, and reform within this quantum world. And they actually link two separate places and two different times. Unfortunately, these real-life time tunnels are just a billion-trillion-trillionths of a centimetre across.

Way too small for a human to pass through - but here's where the notion of wormhole time machines is leading. Some scientists think it may be possible to capture a wormhole and enlarge it many trillions of times to make it big enough for a human or even a spaceship to enter.

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Given enough power and advanced technology, perhaps a giant wormhole could even be constructed in space. I'm not saying it can be done, but if it could be, it would be a truly remarkable device. One end could be here near Earth, and the other far, far away, near some distant planet. Theoretically, a time tunnel or wormhole could do even more than take us to other planets.

If both ends were in the same place, and separated by time instead of distance, a ship could fly in and come out still near Earth, but in the distant past. Maybe dinosaurs would witness the ship coming in for a landing. Now, I realise that thinking in four dimensions is not easy, and that wormholes are a tricky concept to wrap your head around, but hang in there.

I've thought up a simple experiment that could reveal if human time travel through a wormhole is possible now, or even in the future. I like simple experiments, and champagne. So I've combined two of my favourite things to see if time travel from the future to the past is possible. Let's imagine I'm throwing a party, a welcome reception for future time travellers. But there's a twist. I'm not letting anyone know about it until after the party has happened.

I've drawn up an invitation giving the exact coordinates in time and space. I am hoping copies of it, in one form or another, will be around for many thousands of years. Maybe one day someone living in the future will find the information on the invitation and use a wormhole time machine to come back to my party, proving that time travel will, one day, be possible. In the meantime, my time traveller guests should be arriving any moment now. Five, four, three, two, one. But as I say this, no one has arrived.

I was hoping at least a future Miss Universe was going to step through the door. So why didn't the experiment work? One of the reasons might be because of a well-known problem with time travel to the past, the problem of what we call paradoxes.

How to Build a Time Machine: The Real Science of Time Travel by Brian Clegg

Paradoxes are fun to think about. The most famous one is usually called the Grandfather paradox. I have a new, simpler version I call the Mad Scientist paradox. I don't like the way scientists in movies are often described as mad, but in this case, it's true. This chap is determined to create a paradox, even if it costs him his life. Imagine, somehow, he's built a wormhole, a time tunnel that stretches just one minute into the past.

Hawking in a scene from Star Trek with dinner guests from the past, and future: Through the wormhole, the scientist can see himself as he was one minute ago. It just doesn't make sense. It's the sort of situation that gives cosmologists nightmares. This kind of time machine would violate a fundamental rule that governs the entire universe - that causes happen before effects, and never the other way around.

I believe things can't make themselves impossible.

If they could then there'd be nothing to stop the whole universe from descending into chaos. So I think something will always happen that prevents the paradox. Somehow there must be a reason why our scientist will never find himself in a situation where he could shoot himself. And in this case, I'm sorry to say, the wormhole itself is the problem. In the end, I think a wormhole like this one can't exist. And the reason for that is feedback. If you've ever been to a rock gig, you'll probably recognise this screeching noise.

What causes it is simple. Sound enters the microphone. It's transmitted along the wires, made louder by the amplifier, and comes out at the speakers. But if too much of the sound from the speakers goes back into the mic it goes around and around in a loop getting louder each time. If no one stops it, feedback can destroy the sound system. The same thing will happen with a wormhole, only with radiation instead of sound. As soon as the wormhole expands, natural radiation will enter it, and end up in a loop. The feedback will become so strong it destroys the wormhole. So although tiny wormholes do exist, and it may be possible to inflate one some day, it won't last long enough to be of use as a time machine.

That's the real reason no one could come back in time to my party. Any kind of time travel to the past through wormholes or any other method is probably impossible, otherwise paradoxes would occur. So sadly, it looks like time travel to the past is never going to happen. A disappointment for dinosaur hunters and a relief for historians.

But the story's not over yet. This doesn't make all time travel impossible. I do believe in time travel. Time travel to the future. Time flows like a river and it seems as if each of us is carried relentlessly along by time's current. But time is like a river in another way.

STEPHEN HAWKING: How to build a time machine

It flows at different speeds in different places and that is the key to travelling into the future. This idea was first proposed by Albert Einstein over years ago. He realised that there should be places where time slows down, and others where time speeds up. He was absolutely right. And the proof is right above our heads.

A network of satellites is in orbit around Earth. The satellites make satellite navigation possible. But they also reveal that time runs faster in space than it does down on Earth. Inside each spacecraft is a very precise clock. But despite being so accurate, they all gain around a third of a billionth of a second every day. The system has to correct for the drift, otherwise that tiny difference would upset the whole system, causing every GPS device on Earth to go out by about six miles a day. You can just imagine the mayhem that that would cause. The problem doesn't lie with the clocks.

They run fast because time itself runs faster in space than it does down below.

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And the reason for this extraordinary effect is the mass of the Earth. Einstein realised that matter drags on time and slows it down like the slow part of a river. The heavier the object, the more it drags on time. And this startling reality is what opens the door to the possibility of time travel to the future.

Right in the centre of the Milky Way, 26, light years from us, lies the heaviest object in the galaxy. It is a supermassive black hole containing the mass of four million suns crushed down into a single point by its own gravity. The closer you get to the black hole, the stronger the gravity. Get really close and not even light can escape. A black hole like this one has a dramatic effect on time, slowing it down far more than anything else in the galaxy. That makes it a natural time machine.

I like to imagine how a spaceship might be able to take advantage of this phenomenon, by orbiting it. If a space agency were controlling the mission from Earth they'd observe that each full orbit took 16 minutes. But for the brave people on board, close to this massive object, time would be slowed down. And here the effect would be far more extreme than the gravitational pull of Earth.

The crew's time would be slowed down by half. For every minute orbit, they'd only experience eight minutes of time. Around and around they'd go, experiencing just half the time of everyone far away from the black hole. The ship and its crew would be travelling through time. Imagine they circled the black hole for five of their years. Ten years would pass elsewhere. When they got home, everyone on Earth would have aged five years more than they had. So a supermassive black hole is a time machine.

But of course, it's not exactly practical. It has advantages over wormholes in that it doesn't provoke paradoxes. Plus it won't destroy itself in a flash of feedback. But it's pretty dangerous. It's a long way away and it doesn't even take us very far into the future. Fortunately there is another way to travel in time. And this represents our last and best hope of building a real time machine. You just have to travel very, very fast. Much faster even than the speed required to avoid being sucked into a black hole. This is due to another strange fact about the universe. There's a cosmic speed limit, , miles per second, also known as the speed of light.

Nothing can exceed that speed. It's one of the best established principles in science. Believe it or not, travelling at near the speed of light transports you to the future. To explain why, let's dream up a science-fiction transportation system. Imagine a track that goes right around Earth, a track for a superfast train. We're going to use this imaginary train to get as close as possible to the speed of light and see how it becomes a time machine.

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On board are passengers with a one-way ticket to the future. The train begins to accelerate, faster and faster. Soon it's circling the Earth over and over again. To approach the speed of light means circling the Earth pretty fast. Seven times a second. But no matter how much power the train has, it can never quite reach the speed of light, since the laws of physics forbid it.

Instead, let's say it gets close, just shy of that ultimate speed. Now something extraordinary happens. Time starts flowing slowly on board relative to the rest of the world, just like near the black hole, only more so. Everything on the train is in slow motion. This happens to protect the speed limit, and it's not hard to see why. Imagine a child running forwards up the train.

Her forward speed is added to the speed of the train, so couldn't she break the speed limit simply by accident? The answer is no. The laws of nature prevent the possibility by slowing down time onboard. Now she can't run fast enough to break the limit. Time will always slow down just enough to protect the speed limit. And from that fact comes the possibility of travelling many years into the future. Imagine that the train left the station on January 1, It circles Earth over and over again for years before finally coming to a halt on New Year's Day, The passengers will have only lived one week because time is slowed down that much inside the train.

When they got out they'd find a very different world from the one they'd left. In one week they'd have travelled years into the future. Most of the ideas that modern physicists argue about, such as whether time is a dimension or merely a measure of change, whether the past is immutable, or whether human beings have free will so as to affect unfolding events, have been debated for centuries from the scientific, philosophical, and theological angles.

He then opens a most entertaining window into the personalities who gave such great drama to the "golden age of physics" encompassing Einstein's Theory of Relativity and Niels Bohr's discoveries of Quantum Mechanics. Einstein was a physicist who craved order. He thought that in his Theory of Relativity he had found the beautifully designed blueprint of the universe.

Then along comes the Quantum Mechanics crowd with their ideas that subatomic particles are merely probabilities that have no reality until they are measured, of particles spontaneously dematerializing and rematerializing, and of "quantum entanglement" whereby particles on the opposite sides of the universe may "communicate" with each other instantaneously when one of them is measured.

Clegg explains how Einstein rebelled with his whole intellect at this theory of quantum disorder.

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Clegg then explains how the most bizarre effects of Quantum Physics appear in everyday life, such as when a beam of light hits a plane of glass and each photon must "decide" whether to pass through the glass or be reflected back as a mirror image. Because of quantum entanglement the photons appear to "know" the thickness of the glass before they actually pass through it, and, after determining the thickness of the glass, a certain percentage of the photons "decide" to bounce off the front end of the pane.

He also gives interesting biographical sketches of the leading minds of physics including Einstein, Niels Bohr, Max Planck, and Nicola Tesla, who seems to have become insane after his experiments with powerful electromagnetic waves deranged his brain. There are also the discoveries of the less well-known people like Alain Aspect who devised an ingenious experiment to prove beyond doubt the effects of quantum mechanics.

I was also introduced to the work of Ronald Mallett, who seems to be on the current frontier of work in trying to accomplish time travel by warping space through rapid rotation. So, is time travel possible the "fun kind" that is, when you could go back in time and mess around with the past or wing your way into the future to read the winning lottery numbers then come back to the present and place the winning bet? Conventional wisdom, of course, is that this kind of time travel that upsets causality is not allowable in Einstein's Relativistic universe.

The architecture of Einstein's Spacetime sets a minimum and maximum speed for the passage of time time passes at maximum speed when an object is at rest but slows to a crawl when an object is accelerated to nearlight speed but time can't flow backward. However, the random nature of Quantum Mechanics opens up a whole 'nother can of worms. Clegg explains that we now know that photons and certain other particles most certainly do travel faster than light. It happens all the time. Photons can dematerialize and rematerialize on the other side of an impenetrable barrier, thus traversing gaps in physical space in zero time.

Clegg gives the stunning example of how a Professor Gunter Nimtz has made a recording of Mozart's Fortieth Symphony, the recording consisting entirely of microwaved photons that have gapped through space, dematerializing before encountering an impenetrable barrier and rematerializing on the other side. Is it possible, then, to harness Quantum Mechanics so as to dematerialize an object and rematerialize it instantaneously at a different location, thereby by-passing Spacetime, like Star Trek's transporter beam?

Is it possible to use quantum entanglement to transmit information instantaneously between distant objects? Is it possible to use engineering on a stellar scale to create Spacetime-warping "wormholes" that would allow us to jump from any point in Spacetime to any other point, going backward or forward to any desired point in the four dimensions of space and time?

Clegg takes us tantalizingly close to the answer we want to hear, which is "Yes, we WILL be able to discover a way to run around in the past and the future, then come back to the present. The very randomness that goes to the heart of Quantum Mechanics in the end defeats any attempt to apply it in a predictable way to go from point "X,Y,Z,T" "t" representing time to point "X1,Y1,Z1,T1.

He explains how we see evidence of it in every day occurrences such as the double-image in a window pane when photons "decide" whether to be reflected from the glass or to pass through it. Alas, we don't have a way of harnessing the random nature of Quantum Mechanics to make it do the useful work of travelling through space and time the analogy of perpetual motion machines comes to mind but its effects are nonetheless logic-defying. Within its subatomic frame of tiny distances and time frames, Quantum Mechanics makes a mockery of the beautifully structured blueprint of Einstein's Relativity that rules the universe at a macro level.

Because Clegg makes many obscure points in Relativity and Quantum Mechanics clear, because he covers a wide spectrum from physics to the personalities of the scientists who discovered its laws, because he gives the clearest explanation I've yet heard of the current state of knowledge of time travel, and because he writes with delightful clarity that makes his ideas easy to understand, I rate this book five stars.

It's a great read even if you've already read everybody else's take on the subject. Compared to Paul Davies' book, this book is slightly worse. Both books introduce an essentially scientific view of time travel, and in that respect is easily imitated, and not entirely without merit. I found the content, because of the scientific view, somewhat boring and familiar. This is good reading for people who have a casual interest in particle physics, quantum theory and Einstein's general and special theories of relativity as they pertain to the possibilities for time travel and messaging through time.

It is very well written and in understandable language. It reflects the current state of real science as pertaining to time travel. It is an excellent book for anyone that is curious about time travel and for those who are also curious about UFOs and alien encounters. Brian Cl egg knows how to explain hard Science. I have read all of his books. A must read for all those interested in these subjects.

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