For several decades scientists have discovered more and more examples suggesting our universe is seemingly tailor-made for life. A list of many examples is discussed here. One dramatic example is the fact that even though each proton in our universe has a mass 1836 times greater than the mass of each electron, the electric charge of each proton matches the electric charge of each electron exactly, to 18 decimal places, as discussed here (the only difference being that one is positive, the other negative). Were it not for this amazing coincidence, our very planet would not hold together. But scientists have no explanation for this coincidence, which seems to require luck with a probability of less than 1 in 1.000,000,000,000,000,000. As wikipedia states, “The fact that the electric charges of electrons and protons seem to cancel each other exactly to extreme precision is essential for the existence of the macroscopic world as we know it, but this important property of elementary particles is not explained in the Standard Model of particle physics.”
Wishing to cleanse their minds of any suspicions that our universe may not be the purely accidental thing they imagine it to be, quite a few materialists have adopted the theory of a multiverse. This is the idea that there is a vast collection of universes, each very different from the other. The reasoning is that if there were to be, say, an infinite number of universes, then we would expect that at least one of them would have the properties necessary for intelligent life, no matter how improbable it may be that such properties would exist.
I will refer to such a collection of universes as a varying-constants multiverse, since the concept is that the fundamental constants of different universes in this collection would vary. The fundamental constants are items such as Planck's constant, the gravitational constant, the speed of light, the proton charge, the electron charge, and the mass ratio of the proton and the electron.
The question I will consider in this post is: is there any possible way that such an idea of a varying-constants multiverse could be verified?
Why a Varying-Constants Multiverse Could Not be Verified Through Telescopic Observations
You might think that we could verify the idea of a varying-constants multiverse by long-range telescopic observations. You can imagine scientists building some giant telescopes a thousand times more powerful than any ever built. If such telescopes were to allow scientists to look a thousand times farther than they ever looked before, then you might guess that one day scientists might be able to see other regions of space where the constants of nature differ. You might, for example, imagine that scientists looking as far as possible in one direction might see some distant area where the speed of light was much higher, and scientists looking as far as possible in some other direction might see some distant area where the gravitational constant was much different than it is on Earth.
But nothing of the sort has happened, and there is a reason why it cannot ever happen. The reason is that because of the limit set by the speed of light, whenever we look very far away in space, we are looking back in time. So when we look 10 billion light-years away (near the current observational limits of our telescopes), we are looking 10 billion years back in time. Scientists say that our universe began in the Big Bang about 13 billion years ago. So we have a built-in limit as to how far our telescopes will ever be able to look. We can never hope to observe anything, say, 16 billion light years away, simply by building more and more powerful telescopes.
Our most powerful telescopes (such as the Hubble Space Telescope) can look almost as far as humans will ever be able to see with telescopes, which is about 13 billion light years. There is no chance at all that by looking a little farther we will be able to see some sign of another universe. As we approach the observational limit of about 13 billion years, we are looking back a little more to the beginning of our own universe. Scientists say that various aspects of the very early universe and the Big Bang (such as what is called the recombination era) act as a barrier that will forever block us from observing all the way back to the time of the universe's birth in the Big Bang.
So there is no hope at all of being able to verify any theory of a varying-constants universe just by looking farther and farther out in space. But some have suggested two other ways in which we might be able to lend credence to a multiverse theory by telescopic observations: (1) by observing strange, unexplained motions of parts of our universe; (2) by finding evidence of previous cycles of our universe.
The first of these involves the idea that we might be able to see that some fraction of our universe is moving around in an unexplained way, possibly because of gravitational influences by some nearby universe. Such an observation is theoretically possible, but would not actually be any observational support for the idea of a multiverse with varying constants. If we observed such an unexplained motion, it would best be explained by postulating new factors and physics within our observed universe. Even if we were to be forced to conclude that our universe is being gravitationally tugged by some other universe, that would at best be support for the idea that our universe has a “sister universe,” rather than the almost infinitely more complicated idea that there are a vast collection of universes. Moreover, such an observation would provide no support for any idea that other universes have a variety of different physical constants.
The same thing can be said about the idea of finding evidence that our universe had previous cycles. If such evidence were found, it might lead us to think that the universe existed before the Big Bang, and that the universe is older than 13 billion years. But such evidence would not give any basis for believing in anything like a varying-constants multiverse. If our universe had previous cycles, there is no reason to think that its fundamental constants such as the proton charge would change from one cycle to the next. Science knows of no mechanism by which the fundamental constants of the universe could change (here I exclude the Hubble constant, a measure of the universe's expansion rate, which is not really a fundamental constant).
Could we ever verify the theory of a varying-constants multiverse by verifying the theory of cosmic inflation, the idea that the universe underwent an exponential expansion during part of its first instant? No. I may first note that the prospect of being able to verify any theory of cosmic inflation is far dimmer than many now think. It is very doubtful that the current technique being pursued (based on looking for b-mode polarization) will ever provide any real verification. There are many sources of b-mode polarization that are not caused by inflation (gravitational lensing, dust, synchrotron radiation, and others), so trying to find a fingerprint of inflation is like trying to extract a DNA sample from a bandage that was passed around and shared by ten different people with bleeding wounds.
But even if scientists were to confirm a theory of cosmic inflation, that would not verify any theory of a varying-constants multiverse. For one thing, while some versions of the inflation theory imagine inflation producing multiple bubbles of space that might be called other universes, we would have no way of knowing whether such other bubbles of space had ever formed, as they would be forever unobservable. More importantly, we would have no license for assuming that such bubbles of space would be universes with fundamental constants that differed from our own. If one universe produced bubbles of space that branched off to become spatially separated from that universe, the most natural assumption is that such “universes” (or, more properly, other regions of the same universe) would have the same fundamental constants as their parent universe, particularly since science knows of no mechanism by which one universe could somehow produce a different universe with different fundamental constants.
There is still one other technique that might be proposed for verifying the idea of a varying-constants multiverse: the technique of actually launching a mission into another universe. One can imagine some amazing machine that might allow us to travel from our universe to a different universe. In theory, if mankind or its successors were to launch several trips to other universes, and verify that they had different fundamental constants, that might verify the idea of a varying-constants universe.
But there are huge problems with such an idea. The first is that science offers no clue as to how we ever could travel to another universe. The idea seems like pure fantasy, a thousand times more fanciful and extravagant than the farfetched idea of instantly traveling to another star through a space-time wormhole.
The second reason is that if we were somehow to create some machine capable of traveling to another universe, there is no reason to think that it would be capable of traveling back to our universe or sending signals back to our universe (either of which would be necessary for any real verification to occur).
The third reason is that if we were somehow able to create a machine that traveled to another universe, it would still be all but impossible for such a device (or people or robots traveling in it) to verify that the other universe had a set of fundamental constants different from ours. The measurement of our universe's fundamental constants has taken decades of work by scientists around the world. There's no reason to think that a machine transported to another universe would be able to verify that the fundamental constants of that universe were different.
The fourth reason is that if one imagines the scenario of a varying constants universe (many universes, each with random fundamental constants), there would be an overwhelmingly high likelihood (such as 99.999999999%) that any machine transported to such a universe would be instantly destroyed, along with any robots of humans that came along for the ride.
To understand this point, you have to consider the astonishingly high degree of fine-tuning that allows stable matter to exist in our universe. In his book The Symbiotic Universe, astronomer George Greenstein says this about the equality of the proton and electron charges: "Relatively small things like stones, people, and the like would fly apart if the two charges differed by as little as one part in 100 billion.” There are quite a few other cases of fine-tuning required for the existence of stable matter, including fine-tuning of the strong nuclear force.
So if we then imagine a machine being transported to another universe with random physical constants, we have to imagine the machine (and any one inside it) being instantly destroyed as soon as it was transported to another universe. With a 99.9999999% likelihood the coincidences which allow for stable atoms and molecules in our universe would not exist in such a universe. As soon as the machine got over to the other universe, its atoms and molecules would split apart, as the machine would (with overwhelming likelihood) no longer be in a universe which favored the existence of atoms and molecules.
A recruiting poster from 4000 AD ?
Because of these various reasons, we can conclude that there is no substantial possibility that any machine could ever be transported to another universe to help verify the concept of a multiverse consisting of many universes, each with a different set of fundamental constants.
It seems that it is quite impossible to ever verify the theory that there are multiple universes with varying fundamental constants. The theory is neither falsifiable nor verifiable. Consequently, the theory is more of a metaphysical theory than a scientific theory, as all truly scientific theories can be either verified or falsified under some reasonable scenario.