One possibility to explain the constants of nature is that there’s more than one universe.
That we live in a multiverse, with each different universe “sampling” different values of the constants.
There are a few extremely hypothetical ideas in physics that can lead to the multiverse.
One is through the concept of eternal inflation, where the very early universe never ended its period of rapid expansion, and that different portions of the overall multiverse pinched off, so to speak, to create their own bubble universes.
Another path to the multiverse comes from string theory, where extra spatial dimensions can twist up on themselves in a dizzying number of ways.
Each possible arrangement leads to new values of the physical constants, and even entirely new laws of physics.
The range of possible combinations is known as the landscape, with our universe consisting of one point in that landscape.
In these multiverse-inspired ideas, there are a multitude of universes “out there” that don’t support life, but this one does, so here we are.
At the end of the day it’s still the anthropic argument, but at least one that explains how different values of the constants can be realized and created, and it explains why we find these values here: there are a whole bunch of universes that each get different values of the constants, but this one produces life, so here we are.
There have even been attempts to estimate if our kind of universe is common or not.
These calculations run into…a whole bunch of issues, the biggest one being we have no idea what the prior probability is for any particular combination of constants.
We can’t assume that they’re all equally likely, and without that then we can’t assess likelihoods…so all those attempts are doomed to fail because of this fundamental ignorance.
So perhaps the multiverse slash landscape is slightly more satisfying than the usual anthropic argument, but not by much.
But leaving aside the ability to calculate probabilities, there are additional issues with both of these ideas.
For one, they are both hypothetical and not supported by any available evidence. We don’t know how regular inflation works, and whether eternal inflation is even possible.
And string theorists can’t make the connection between a particular arrangement of the extra dimensions and the physics that it generates, meaning that we can’t even make testable predictions.
So grounding your argument in unsupported, super-duper-hypothetical ideas isn’t exactly the best way to move forward.
What’s more, eternal inflation and string theory contain constants of their OWN that are not “explored” by different iterations of the multiverse.
For example, eternal inflation requires any number of extra, unknown parameters to make it work – it assumes that inflation is there and doing its thing and proceeding in a certain fashion, with all that physics governed by certain constants.
And string theory has assumptions itself, like a certain number of extra dimensions; a number that is not predicted by the theory itself.
So that doesn’t seem like a satisfying conclusion either – no matter what, you still end up with SOME numbers that you can’t explain from pure theory.
But that may count as progress, if we are able to explain many of our current constants, and trim the total number of unknowns down a bit, we may feel like we’re getting closer and closer to a fundamental theory of physics, one that is able to explain everything about all the things.
But the truth is, we may NEVER be able to get rid of the constants. There may always be bundles of ignorance that we cannot eliminate.
I mean, that kind of makes sense: at the end of the day, no theory of physics, no matter how sophisticated, can ever explain its own existence. So maybe this is the limit, and we just have to get used to ignorance.
But that doesn’t sound fun. This is what keeps physicists going, is the belief that there’s always more to learn right around the corner.
And of course there is the opportunity here for…let’s call it divine intervention. That’s not exactly physics which is the whole point of the program but I’m not going to hold you back because all of our other ideas are…let me see here…yup, absolutely terrible.
Like I said, none of the answers are all that satisfying. As far as we can tell, the constants really are constant.
They don’t change in space or in time. And however you count them, you will always find a list of numbers that are central, core to all our theories. They just exist, without explanation and for no apparent reason.
For now, until we find one to change in time or make some major theoretical headway, we’re just going to have to live with it.
Written by Paul Sutter/Universe Today.
