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

Author:Brian Clegg [Clegg, Brian]
Language: eng
Format: epub
Tags: Science, Physics, General
ISBN: 9781250024220
Google: IT4vLwEACAAJ
Amazon: 1250024226
Publisher: St. Martin's Press
Published: 2013-04-15T16:00:00+00:00

This way of representing the equations does cheat a little. They are equations in more than one dimension, working on matrices of numbers rather than a single value. So the upside-down triangle, called a “del,” involves change in all three spatial dimensions simultaneously. However, you don’t need to understand the math for the equations to give you a broad feel for the elegant simplicity of Maxwell’s discovery.

The first shows how a changing magnetic field produces electricity. The second shows how electricity generates magnetism. The third gives us a way to link the electrical field that is produced to the electrical charge present. And the final one tells us that there can’t be isolated magnetic poles (so called monopoles): they always come in matched pairs.

The mathematical description of light based on Maxwell’s work had one oddity that was largely ignored at the time. There is more than one way to solve the equations. You may remember solving quadratic equations at school. Each equation had not one, but two possible solutions. Similarly, Maxwell’s equations predicted that light should have two modes of operation, what were called “retarded waves” and “advanced waves.” The retarded waves are light as we observe it, but the advanced waves should travel backward in time—still at the speed of light, but in the reverse direction on the timeline.

If it was somehow possible to use an advanced wave to send a communication to a distant beacon, then send another advanced wave back to the original source, the message should arrive back before it was sent.

Advanced waves have never been observed, and for a long time it was assumed that they were just a peculiarity of the math, and there was no physical phenomenon to correspond to the advanced solution, leaving only the retarded solution, the familiar light that travels forward in time. But there was always a school of thought that assumed the advanced waves were present, just not observed. Apart from anything else, there was no scientific reason to abandon the mathematics that predicted advanced waves. They were just arbitrarily being ignored because they didn’t seem to make sense.

There is something of a parallel between advanced waves and the idea of virtual particles. The electromagnetic interaction between, say, an electron and the nucleus of an atom involves a flow of photons between the electron and the positively charged nucleus. We never see these photons—they never escape into the real world, so they are referred to as virtual. But virtual particles can be shown to exist by disrupting the environment that contains them, “exposing them” to the real world. Some argued that advanced waves were a bit like this—present, perhaps even significant in the workings of the universe, but not observable, because of our thermodynamically biased arrow of time.

Two of the greats of twentieth-century American physicists, John Wheeler and Richard Feynman, suggested that there was a circumstance where advanced waves did have a visible effect. When an atom gives off a photon of light, the atom recoils, like a gun recoiling when it is fired.

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