How dependent is the Universe on initial conditions?

[Philosaur]

I just finished watching George Smoot's TED talk on the Design of the Universe.

In it, he says that "tiny fluctuations" in the otherwise smooth distribution of matter were ultimately responsible for the structure we see in the universe. My understanding is that those fluctuations are the result of random quantum events in the earliest moments of the big bang.

First, is it correct to say that the particular outcomes of the various collapsing waveforms, along with their number, position, and timing, gave rise to fluctuations in the uniform field of matter and energy, which in turn became areas of greater density in the cosmic background radiation, which later became the galaxies, nebulae, stars, and everything else?

Second, is it possible that differences in the details of those initial quantum events (number, position, timing, etc) could have resulted in a greatly different overall structure? For instance, could it have resulted in a universe where galaxies were orders-of-magnitude more numerous, but with orders-of-magnitude fewer stars?

Third, could differences in the details of the initial quantum events have resulted in qualitative differences in the universe? Like a different value for Einstein's constant, or different laws of physics? (It seems this isn't likely, but I'm not certain if the symmetries of physics hold true over other possible universes.)

 

[epepke]

First, is it correct to say that the particular outcomes of the various collapsing waveforms, along with their number, position, and timing, gave rise to fluctuations in the uniform field of matter and energy, which in turn became areas of greater density in the cosmic background radiation, which later became the galaxies, nebulae, stars, and everything else?

Wavefunctions, not waveforms. And you don't really need the concept of collapse, which is only present in some interpretations. Sorry.

Second, is it possible that differences in the details of those initial quantum events (number, position, timing, etc) could have resulted in a greatly different overall structure? For instance, could it have resulted in a universe where galaxies were orders-of-magnitude more numerous, but with orders-of-magnitude fewer stars?

Probably not. It seems plausible, given chaos theory. However, the best current theories suggest that the inflationary phase smooths out a lot of the properties of the universe overall, such that a fairly large variation in initial conditions will still result in the same sort of universe, though not in particular details.

So all the important constants would still be close enough for jazz.

 

[Philosaur]

Wavefunctions, not waveforms.

Noted.

And you don't really need the concept of collapse, which is only present in some interpretations. Sorry.

Why sorry?

But since these are just different interpretations, isn't it the case that it doesn't matter (i.e. makes no measurable difference) whether we call it "collapse", or the spawning of another world (per MWI), or some other phenomenon from some other interpretation? I'm not saying we'll never be able to differentiate, but for now that's the case, right?

So all the important constants would still be close enough for jazz.

I just hope that these other possible worlds still contain Vonnegut, Stan Lee, and Blue Bell Pecan Praline Ice Cream.

 

[rwguinn]

Everything depends on the initial conditions.
An a ninjaneer, I find that 90% of all analysis problems tend to be because somebody screwed up the Boundary/Initial conditions...

 

[Wowbagger]

Initial conditions are responsible for all of the proximate details about everything in the Universe. But, it is possible that, no matter how those initial conditions were, chances are a lot of the ultimate effects in the Universe would still take place.

For example: Planets with life on them would probably come about, even if the conditions were different, but those lifeforms would probably look a lot different.

 

[Mikemcc]

Even if the initial conditions are very particular, we would only be aware of them because they are the conditions that allowed us to evolve to observe them.

 

[sol invictus]

First, is it correct to say that the particular outcomes of the various collapsing waveforms, along with their number, position, and timing, gave rise to fluctuations in the uniform field of matter and energy, which in turn became areas of greater density in the cosmic background radiation, which later became the galaxies, nebulae, stars, and everything else?

Yes.

Second, is it possible that differences in the details of those initial quantum events (number, position, timing, etc) could have resulted in a greatly different overall structure? For instance, could it have resulted in a universe where galaxies were orders-of-magnitude more numerous, but with orders-of-magnitude fewer stars?

Not unless you change something in the theory. The quantum fluctuations have a particular probability distribution that is determined by parameters and field content of the theory. While more or less anything is possible, the probability that if you ran the universe again with the same theory you'd get orders of magnitude more galaxies is extremely small.

Third, could differences in the details of the initial quantum events have resulted in qualitative differences in the universe? Like a different value for Einstein's constant, or different laws of physics? (It seems this isn't likely, but I'm not certain if the symmetries of physics hold true over other possible universes.)

No one really knows the answer to that. Certainly we know how to write down quantum theories that incorporate everything but gravity in which that is impossible - the laws are fixed. But when you try to incorporate gravity fully, you get theories like string theory, and in string theory Newton's constant (I think that's what you mean by "Einstein's constant") can indeed vary, as can all the other low-energy laws we observe. There are still some features that cannot and do not vary (which makes string theory falsifiable), but nearly all "constants of nature" are actually not constant.

 

[epepke]

Why sorry?

But since these are just different interpretations, isn't it the case that it doesn't matter (i.e. makes no measurable difference) whether we call it "collapse", or the spawning of another world (per MWI), or some other phenomenon from some other interpretation? I'm not saying we'll never be able to differentiate, but for now that's the case, right?

Yeah, it really doesn't matter. I just see this concept of wavefunction collapse as given far more importance than it really has, and I'm a bit touchy about it.

 

[Philosaur]

Even if the initial conditions are very particular, we would only be aware of them because they are the conditions that allowed us to evolve to observe them.

Yup: that's the Anthropic Principle.

 

[Philosaur]

Yes.

Awesome. College wasn't a waste after all!

Not unless you change something in the theory. The quantum fluctuations have a particular probability distribution that is determined by parameters and field content of the theory. While more or less anything is possible, the probability that if you ran the universe again with the same theory you'd get orders of magnitude more galaxies is extremely small.

You've answered my question admirably--I understand what you're saying.

But the way you word this ("...if you ran the universe again with the same theory...") raises another question, and I'll see if I can do it justice here.

I think it's fair to say that physical theories are the result of observing physical facts. If it was the case that we lived in one of those highly unlikely universes where matter was distributed much more smoothly (i.e. more galaxies, fewer stars per galaxy), would the resulting physical theory be able--in principle--to give any indication of just how extraordinary and unlikely that universe is? (I grant that I may be missing something here, but it seems like there may be some chauvinism in our assignments of probabilities to alternate universes. Not that I'm losing sleep over it.)

No one really knows the answer to that. Certainly we know how to write down quantum theories that incorporate everything but gravity in which that is impossible - the laws are fixed. But when you try to incorporate gravity fully, you get theories like string theory, and in string theory Newton's constant (I think that's what you mean by "Einstein's constant") can indeed vary, as can all the other low-energy laws we observe. There are still some features that cannot and do not vary (which makes string theory falsifiable), but nearly all "constants of nature" are actually not constant.

I did mean Einstein's constant, but if that doesn't make sense in this context, then I'm happy to substitute Newton's constant. [After a little reading, it looks like it might be best to say "the gravitational constant". But please correct me.]

In any event, thanks for the answers!

 

[sol invictus]

I think it's fair to say that physical theories are the result of observing physical facts. If it was the case that we lived in one of those highly unlikely universes where matter was distributed much more smoothly (i.e. more galaxies, fewer stars per galaxy), would the resulting physical theory be able--in principle--to give any indication of just how extraordinary and unlikely that universe is? (I grant that I may be missing something here, but it seems like there may be some chauvinism in our assignments of probabilities to alternate universes. Not that I'm losing sleep over it.)

Our theories are probabilistic, and they assign non-zero probability to more or less every possibility. So.... all we can say is that the parameters of the theory are probably in some range, and then we can make predictions with the theory or theories in that range. But the probability for something like what you're asking is exponentially small (in the ratio of the actual density to the expected density, roughly), so very discrepant results are extremely unlikely.

I did mean Einstein's constant, but if that doesn't make sense in this context, then I'm happy to substitute Newton's constant. [After a little reading, it looks like it might be best to say "the gravitational constant". But please correct me.]

I'd never heard of "Einstein's constant", but if it's defined as per that wiki page, then it's essentially identical to Newton's constant - so same answer!