Many Worlds and Television Interference
TL;DR – There may be infinitely many parallel worlds but there is nothing to be detected.
A friend of mine is really into science fiction. “Did you know that there are infinite parallel worlds?” “And that there are infinitely many you and me, each a little bit different?” “And one day we will be able to travel to these different worlds, and taste all the different variations of pizza?” I wish I were in a universe in which he didn’t go on and on.
The whole idea of parallel worlds is something very very appealing. I mean, to science fiction writers. It allows to explore a whole range of what-if scenarios without messing up your main story line. Like what if your heroes actually were cat-people or something. This creates a lot of drama, or so I am told.
Unfortunately, one may get the impression that these ideas are somehow physically relevant, because it’s SCIENCE (fiction). It doesn’t help that the best physical theories we have are a bunch of mathematical equations which are then “interpreted” after the fact… like the Oracle of Delphi. Moreover, it seems that some have trouble distinguishing the case in which they forgot whether they parked their car in the front or in the back of the building, from the case in which they sawed it in half and distributed in the two places. Probability theory can be very confusing.
But let’s suppose there are other universes out there, all parallel parked. Are they relevant for the purpose of physics? Can we detect them? Can we communicate with people, or cat-people, in those realities? Let’s explore the question with a tangibly abstract thought experiment.
Television interference
When you were little you watched way too much sci-fi television. It inspired you to go into science and now you are disappointed because science is a lot less exciting than it looked on the telly. You really wanted a sonic screwdriver.
So, you decide to do something new and exciting. You heard about the SETI program: the Search for Extra Terrestrial Intelligence. This is where people look for signals coming to earth that may have been generated by alien civilizations. Basically, they try to watch alien television. Apparently, they believe we don’t have enough television programs here on earth… Anyway, what you want is the SPWI: the Search for Parallel-World Intelligence. You want to detect television programs coming from alternate realities.
So you start creating a receiver for this purpose. The first problem you find is that it’s picking up all the terrestrial television signals. Normally you’d be interested in those… you watch a lot of TV. But these are not the shows you are looking for. So you start devising a way to remove those unwanted signals.
After a few years of work, you are successful in removing the noise and you finally have a new signal! One that was not created on earth! You are very excited, but you realize that it’s not from a parallel universe… it seems to be coming from Kepler-442b, an exoplanet in orbit of Kepler-442. What a bummer! Plus their transmission is full of commercials. So you start devising ways to remove all these other unwanted signals.
While you are doing that, though, you realize that you may have a problem. To be able to detect the TV signal from one of the parallel universes you need to separate it from all the others. But there are infinite worlds… So what you would actually detect is the sum of the television signals from an infinite number of worlds. This signals would all be statistically uncorrelated. And the sum of infinitely many uncorrelated signals gives a Gaussian distribution. So what would you be detecting is random noise.
Moreover, the strength of the total signal cannot be more powerful than the earth TV signal. I mean: we can watch earth TV fine. So, the total alternate dimension signal must be finite. But there are infinitely many universes, so the signal coming from each one must be undetectably small, basically zero strength.
You decide to abandon science and become a science fiction writer, where your imagination needn’t be constrained by technical problems.
Noise and signal
A person much better at gardening than me once said: a weed is a plant in the wrong place. In the same vein, noise is a signal you are not interested in. Nature does not really distinguish between plants and weeds, between noise and signal. We do. We get both and then, depending what we want to do, we differentiate and filter.
This is something that engineers and experimental scientists are well aware of, but most other people don’t seem to realize. When you build a giant antenna to detect gravitational waves, you actually build a giant antenna that detects a lot of things. It may detect the train/subway/planes passing by. It may detect the vibration caused by thermal fluctuations. It may detect the imperfection in your laser source. That is, it detects everything including gravitational waves. So you have to be clever and find ways to remove the noise.
But no matter how much you remove, you can’t remove everything. What’s remains is your background. And you always have a background. It’s like pulling weeds: there will always be some around but you stop when you can finally see the plant you like. So you stop when the background is lower than the signal you are interested in. But if there are infinitely many similar signals all at the same strength, and you want to pick up one between them, your background is always going to be higher than your signal. You can’t distinguish it from the noise.
So, the next time you see a TV show that tells you that there are infinitely many worlds, in which all possible choices are executed, and you see the hero traveling to them, realize this: he wouldn’t be able to physically tell one apart from the other, so he would not be able to travel to a particular one. Ergo, each infinitesimal part of his body would go to one of the infinitely many alternate realities. Now, that’s a show I’d like to see!