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A Home Test for Parallel Universes

by Sam Sachdev
March, 2004

When you think of a parallel universe, do you think of a universe, or a world, similar to ours but different in some fundamental quality. Bill Clinton, for instance, is a happily celibate priest. Or George W. Bush delights his fellow Mensa members, at parties, with his verbal games. Or, perhaps, you only have a science-fiction quality vagueness to what you think of a parallel universe: pointed ears, warp-drive through worm holes, and form fitting Lycra body suits on a thin, well-groomed crew. A parallel universe, it may surprise you to learn, is actually detectable in your own home, office, or almost anywhere indoors. All that’s required is a red laser pointer, a pin, and a piece of paper.

With the aid of David Deutsch, a physicist at Oxford University and his excellent book “The Fabric of Reality”, the experiment, in a step-by-step process, is going to be set-up and, then, it’s going to be explained why this magic-like result from this experiment is indeed proof of a parallel universe.

First, a red laser pointer is needed. I found one at Radio Shack for $19, not including the triple A batteries that were needed. The red color of the laser pointer is important. The red light, unlike the white light of a flashlight, which is a composite of many colors, doesn’t fray as white light does. The red light, specifically, of the laser pointer casts more specific shadows – which is what this experiment does. A flashlight, according to Deutsch, can probably be substituted. A filter, however, is going to have to be placed over the white beam. The filter, can only be red colored glass; paper or any other filter won’t work.

Next, a relatively large, dark room is needed. The room should be large enough to set up the laser pointer on, say, a table, and have it cast its light on a wall about one and a half meters, or about five feet away for my metrically challenged Americans. At first, this humble journalist tried to do the experiment, during the bright light of a Washington, DC winter day, in a walk-in closet and a bathroom. Both weren’t large enough. My dining room, when the sun had set, was.

David Deutsch recommends a room that’s almost totally dark. I found, however, that this was too dark. The experiment requires enough light to manipulate the laser pointer. What I did was have a light on in another room, which provided enough light to see what I was doing but dark enough to see the shadow cast by the laser pointer.

The experiment is best done with done with two people, with one handling the laser pointer and the other observing the pattern on the wall. The positions can then be switched. Be careful, however, not to shine the laser light into the other’s eyes.

If you don’t have two people, this is what I recommend. Fold a piece of paper in half and place it on the table, so that one half is perpendicular to the table. Then, using a book, or anything to set the laser pointer on, aim the pointer at the paper. Mark where the red light hits the paper. Using a pin (and only a pin, not a tack, the holes have to be as small as possible) punch two holes, on the mark, as close to each other as you can. Then, aiming the laser pointer at the two small holes, a shadow of five slits should be cast on the wall. That is, there’s going to be one large red dot cast on the wall. In the dot, there should be five distinct shadows cast by the two holes. If this doesn’t work, the most common problem I found was that there wasn’t enough distance between the paper and the wall. If possible, increase the distance. David Deutsch recommends about five meters, or fifteen feet, but I found about five feet, or a meter and a half, was enough to observe the pattern.

Why, you may be wondering, are there five slits of shadows when there are only two holes? That's because light, as you may have guessed, usually travels in straight lines. We can’t, for instance, see around corners or buildings. When light, however, is forced to go through a small hole, it acts like a thirteen year old forced to go clothes shopping with their parents, it rebels. Specifically, it bends. The smaller the hole is, the more it bends. So, if light traveled in straight lines, there would only be two shadows cast by the holes. Instead, however, the shadow of the five slits, from the two holes, is a result of concentric rings of varying thickness and brightness. There is a bright spot in the center, surrounded by a dark ring and, following this pattern, fainter rings of light and darkness around it. The result is the pattern of the five slits.

Patiently, you’ve read this far and want to know when you’re going to detect a parallel universe. This is the next step.

Next to the two holes you’ve punched, make two more. It’s important that they be parallel with the other holes and that they be as close to the other two. Also, keep in mind that the width of the point of the laser is narrow (at least mine was) and that the laser has to go through all four holes simultaneously.

What should happen, or is expected to happen, is that the same pattern as with the two holes appears. Light beams, according to “Fabric of Reality”, normally pass through each other unaffected. So, the same pattern as the two holes, should be repeated, only brighter and slightly blurred.

What happens is nothing like that and is, David Deutsch believes, evidence of parallel universes. Only three shadows are cast. That is, two of the shadows disappear. If you look closely, you’ll see that where there been two red shadows are now dark. So, punching two more holes actually results in two of the shadows going dark.

How does this happen? Something, obviously, is blocking the light from casting the shadow. Or, you might think that the photons, individual units of light, have somehow been bent and recombined to form a pattern of new shadows. The answer, as will be explained, can’t be this but is an usually undetectable world of photons, or, a parallel universe.

First, however, it should be explained that what interferes with the laser light has the properties of light. If, for instance, two of the holes are covered by anything opaque, the five slit shadow reappears, but it, the red laser light, can penetrate anything and behaves as light does, that allows light to pass. If, for instance, a system of mirrors is set-up, which the light bounces off of and eventually reaches the wall, the same patterns appear.

What happens when the red laser light is slowed to one photon at a time (no, this can’t be done in your dining room)? That is, when only one photon is fired through each of the four slits, the same pattern appears. Could it be that, when the photon passes through the slits, they change course and recombine? Nope. When detectors are placed at each of the four slits, and one photon again is passed through them, only one of the detectors goes off, meaning that the photon hasn’t split.

David Deutsch, using an experimentally confirmed prediction from quantum theory, believes that what’s causing the interference are shadow photons. More specifically, interference, as in this experiment, is not only common for photons but for every particle. So, Deutsch writes in “Fabric of Reality”, this is what is causing the interference, “[W]hen a photon passes through one of four slits, some shadow photons pass through the other three slits.” The shadow protons, then, are blocking the tangible protons, causing only three shadow slits.

These shadow protons form a parallel universe. David Deutsch writes that they behave as tangible particles do. They obey the law of physics but with the difference that they’re in a different position.

But how, exactly, do the shadow protons stop the tangible ones? The answer that Deutsch presents is that the shadow atoms, present in the shadow protons, form a barrier. Only a small proportion of the tangible and shadow atoms, however, are interacting with one another. Or, as Deutsch writes, “each shadow atom in the barrier can be interacting with only a small proportion of the other shadow atoms in its vicinity, and the ones it does interact with form a barrier much like a tangible one. And so on. All matter, and all physical processes, have this structure.” To clarify his last point, the parallel universe interacts with the tangible universe in much the same way as particles so in the tangible universe: only a small proportion do. The result is through interference, or weakly, as in the experiment.

Why, you may be wondering, if there’s a detectable parallel universes around us, why don’t we detect, or notice it, more often? David Deutsch writes, the answer, “...can be found in the quantum-mechanical laws that govern them.” Every particle, for instance, has counterparts in other universes and is only interfered with only by those counterparts. Any other universe, therefore, can only be detected when the particle in, say, our universe converges with its counterpart in another universe. The path of the particle and its counterpart have to be exactly right. They have to separate and join together again, as in this experiment, and the timing has to be right. If there’s a delay in the particles or any interference, the particles won’t converge. Also, a parallel universe is only detectable between universes that are very alike. In short, because these events are extremely rare, so is the detection of parallel universes is difficult.

It should be added that most physicists disagree with Deutsch’s conclusion that what is detected in this experiment is another universe. For brevity’s sake, the argument against can be summarized as, there is something interfering with the light in this experiment, why does it have to be a parallel universe? Why can’t it be just be left to something that we don’t yet understand?

If you’re interested in how Deutsch answers his critics, I recommend the “Fabric of Reality” for his answers and reasoning.
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