RUTA said:
I was away while I was working on this very problem, actually. I bailed on all discussion forums during this time to focus on the problem at hand. I do believe the Nobel citation should not have stated "for the discovery of the accelerating expansion of the Universe," since that conclusion follows from their data only in the context of a particular theory of cosmology. They certainly deserve the prize, but the citation should have said something like, "for observational techniques associated with type Ia supernovae." Then, the Nobel committee doesn't have to worry about changes to our theoretical cosmology that change the interpretation of the data.
I agree, because even after it's proven wrong, using type 1A supernova will still be useful, and we'll just need to consider an extra variable of our local dark flow or whatever else is causing our relative acceleration. However, the average person wouldn't understand what the big deal with type 1A supernova is, so I can understand the naming the Nobel committee used.
I also can see why they picked to honor it now because of the threat of evidence mounting against universal acceleration of expansion. Good science is good science, even if they are eventually shown to be "wrong" because they missed some detail. Newton was eventually shown to be "wrong", for instance, however Newtonian physics still accurately describe specific macro-phenomena like how two billiard balls will interact at the macro level when we don't need to be so precise to consider the minute relativistic and quantum level effects. Einstein may be shown to be "wrong", especially if we can't refute the CERN neutrino results (if this doesn't turn out to be some experimental error). But then it will probably be some edge case / exception, and not the general rule. So "right" or "wrong" isn't the best way to look at it, but instead experimental and mathematical results add conditions to previously accepted theories. Most theories are eventually found to be incomplete, but if they stood the test of time for a while then they are at least correct in some limited scope. So in that light, the men being honored still did a good job.
AFAICT, you will not end up with an "exact copy" of the early universe, if you tried to reverse the current expansion for 13.75 billion years...
Doesn't the "no cloning" theorem prevent that? Or is it allowed as long as the "exact copy" doesn't exist simultaneously as the original?
Edit: No, in both Copenhagen and revised Everett interpretations, ways around "no cloning" exist for this discussion as long as no exact copy is made but instead separate measurements are made on the same quantum wave function. Instead, quantum decoherence is the issue. QC is reversible but wave function collapse isn't. See later.
True, but it would be a terrible bad "illusion", because of the change of the direction of time; watching the omelet jumping out of the pan to 'regenerate' into 4 complete eggs... we would just know that there’s something 'fishy' going on...
Or?
That would be interesting and I've thought about this quite a bit. I think our view of causality is biased and people who were experiencing everything backwards would just be used to it.
Edit:
Well, yes. But that is as much true classically as it is quantum-mechanically. This is a practical limitation, not a fundamental one.
Edit: Actually, let me amend that slightly. It is a fundamental limitation in the sense that the information needed to contain the full state of the universe would require a computer more complex than the entire universe. So in that sense it is a fundamental limitation. But what I'm trying to say here is that quantum mechanics doesn't change anything, at least not as far as this is concerned.
I agree more with your Edit better than your first statement but complexity of the computer is irrelevant when no computer is powerful enough to solve a problem. You seemed to have taken a "hidden variable" interpretation and believe there is actually a deterministic state versus a probabilistic one and that we can fully "know" the state if we crunch hard enough and have a complex enough computer. I can't read for sure if that's your viewpoint, or if you were just using terms that have different meanings in Computer Science. It's a common misconception that since you can describe the entire universe as a wave function, that you can deterministically describe its state. I'm a Computer Scientist and have also studied quantum computing and the mathematics behind it (which sadly isn't required study yet at most universities). It is useful when having these discussions to refer to theories of both classical and quantum computation and just view the universe as a giant quantum computer with some gates that perform a measurement to break superposition and create classical states (through decoherence). First of all, we do not know yet whether a classical computer can be as powerful as a quantum computer, and the general consensus is "no". Nevertheless, even if a classical computer could do everything a quantum computer can do, and therefore an ideal turing machine (the most powerful classical computer possible) could model the universe's classical states and superpositional states, then you still have another fundamental blocker: You can crunch all you'd like, even with an ideal turing machine -or- a quantum computer for that matter, and you'll never be able to deterministically "calculate" the "the universe" in a way you could predict 100% what the next state was going to be. This has been shown mathematically using a combination of the undecidable halting problem and Godel's incompleteness proof to show a T.O.E. can never completely describe the universe in a predictive way. The best you can do is an approximation, a probabilistic result!
This is a lot more than a practical limitation, it is a fundamental blocker. http://adsabs.harvard.edu/abs/2008PhyD..237.1257W"
However, all that is irrelevant since unitary quantum calculations are reversible, and therefore every part of the universe that's in quantum superposition is reversible. Of course, the classical states are reversible. What isn't reversible, unfortunately, are the wave function collapses "due to measurement" (really due to quantum decoherence). Therefore, at best, the universe could have a certain probability of reversing into the same state it was before. However, to say that it is 100% likely to reverse into the same state is not something we can acertain unless the universe had a completely known state which is not possible.
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