Discussion about Theoretical Physics - The Multiverse, Time Travel, and Other Related Topics

This is a thread to discuss topics with issues relating to speculative physics that don't fit with the topics in other threads, such as the Global Warming thread. Don’t bring up past grievances or arguments from another thread into this one. If you have a problem with someone, take it to PMs. I typically will not block people unless they make low-quality posts frequently, so back up your claims with sources, try to make your arguments clear, and have fun with it.

To start off, should the multiverse be considered, "scientific"?   

oh heck yes

I love talking about this stuff

However, the multiverse (right now) is untestable. Therefore, is it science?

@TerminatorUC800 you're active again?

It's worth mentioning first of all that there seem to be a surprising number of distinct hypotheses using similar or identical terms. These have been classified by different theoretical physicists.

All these hypotheses are scientific in the sense that they are associated with models that make predictions. They are valid in the same way as all of the interpretations of quantum mechanics are valid. They all predict the exact same things, so there is no way for science yet to distinguish between them.

Some Multiverse hypotheses may be differentiated by scientific tests in the forseeable future. Ideas include probing the very early Big Bang using gravitational wave astronomy and looking for statistical hints that there is more than our Universe. The details are obscure to me.

Scientific theories have no essential requirement to be the simplest to explain the facts, but I believe the Everett Interpretation is in a sense a particularly simple interpretation of quantum mechanics, with a global continuous deterministic evolution obscured by us seeing just one branch.

Given that, it is worth emphasising that the Everett Interpretation is no less scientific than Schroedinger's or Heisenburg's interpretations. It is a model predicting the same observations. There is a substantial untestable component to every model of quantum mechanics - the workings that are used to do calculations but cannot be observed.

Some people consider the Multiverse as unscientific because there's currently no valid ways of testing for it.  People say the same things about the whole "universe is a 2d projection/simulation" theory.  How can you test for something outside the universe from inside it, while subject to its laws?

But there are lot of theories people posit that are not going to be immediately testable; that does not preclude the idea itself from being a "scientific" theory...but, in the absence of realistic testing and progress, it does preclude it from being called a science.

Having said there's no way to test it and it's not a science, just a theory...I am a fan of the Multiverse theory.  There's a school of thought that says that if something can't be tested, it's pointless to consider it.  The universe is an expanding "bubble", effectively.  We don't know if there are other bubbles expanding outward that will intersect our universe, or if the classical Multiverse tapestry model is correct (I call it the "bubble wrap" theory because it generally posits a set of universes adjacent to each other but not ever interacting.

I tend to think those models are biased towards a 3d viewpoint of how a multiverse would actually exist.  I have my own theory (for over a decade now), which I call "Dandelion Theory".

Every particle in our universe right this instant has a set of properties, and two of those properties are velocity and direction...a vector.  The particles are moving through largely empty space in our universe each with its vector.  That's our perception.  Now freeze all the particles, and then imagine them exploding in all possible directions at once, at all possible velocities...it helps if you imagine it like a dandelion.  A series of neverending explosions of vectors.  This visual doesn't hold up as an analogy, but it helps with understanding the concept.  People talk about infinity all the time, but when you talk about a notion like this, they balk at the idea.  If there's an infinite multiverse comprised of infinite universes, though, then "infinity" actually holds up, and the idea of something you can posit or imagine *not* existing becomes impossible.

What if these infinite number of universes exist in the same domain, with a unique particle signature like a DNA sequence that determines their properties, physics, etc. and only that matter (and energy...or possibly exception there?) which shares "our" universe's signature can interact with us or be perceived by us? 

Infinity is more comforting a concept than nothing.  Which is why I like the idea, so there's inherent bias there (for most human beings).  But applying Occam's Razor...I don't see that there's any particular reason the Big Bang should occur at random, or that if it does occur at random, that a singularity exploding outward and eventually decaying down into heat death and unimaginable distance between inert particles should be the totality of existence.  It's inelegant, and begs more questions than it answers at a meta level.

In an overly simplistic way, I'm saying something like this:

- Since something exists as proven by your reading this and understanding it right now, "nothing" doesn't not exist.  An entire universe with one particle in it is still "something" and not "nothing".

- You can posit that "nothing" existed followed by something popping into existence.

- Positing something from nothing is no better or worse in theory than positing that there was always something.

- At the most fundamental level, if you are going to posit "something", but then place limits on it that allow for "nothing", why is that necessarily more valid than positing "everything, since always", i.e. infinity?

String theory posits the same kind of "signature" idea, and posits that there are 10^500 signatures possible, each with its own set of properties/laws.

...I'll probably add to this later.

I didn't say it it was unscientific, I am saying it hasn't got enough oomph yet to be called a science.  And I would say it would have to be separate branch of physics, dealing with things outside of our own boundaries.  That was my whole point.  It's not unscientific.

Presently it (the multiple worlds interpretation of quantum mechanics) has not taken the step to being more than an interpretation of quantum mechanics. It describes what can be understood to be a lot more (all sorts of different things happening in different branches, but it predicts nothing more.

There is no clear way at present for this to change, so the more will be predicted as well. Until then we are completely in the dark. Descriptions of things we can never observe in any way are moot.

Without various sci-fi and/or other imaginings of a multiverse, the theory would never have been advanced to being with.  What does need to be said is that allowing such imaginings to influence research/experimentation would not be following the scientific method.

What about Kip Thorne’s method? Use a wormhole to connect two different regions of time with a different rate of time, thereby enabling a form of “time travel”.

If there is a multiverse, Everett’s interpretation is the most likely option. Right now, I prefer quantum decoherence to explain the issue of measurement, but if not that, the quantum multiverse seems best. 

I have been for a while. I’ve mostly been in clubs or obscure threads.

Determinism is not true in our Universe. This is a conclusion based on experiment (specifically Bell's experiments).

I don’t know how one could possibly know the difference between something being truly random or having an unknown cause.

Learning quantum mechanics.

I never recall saying that. You are far too versed in pop culture to be six years old anyway.

A non-answer.