What's the universe collapsing into?

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Discussion Overview

The discussion revolves around the concept of wavefunction collapse in quantum mechanics, particularly in relation to the idea of a universal wavefunction and its implications for understanding the past, present, and future states of the universe. Participants explore various interpretations of quantum mechanics, the nature of knowledge accumulation over time, and the relationship between wavefunction collapse and entropy.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that individual wavefunction collapses could represent a slow collapse of a universal wavefunction, questioning what state it might be collapsing into.
  • Others argue that the notion of wavefunction collapse is misleading and suggest alternative terminology, emphasizing that it does not imply an increase in information.
  • There is a discussion about the certainty of past events versus uncertainty of future events, with some suggesting that accumulating past knowledge does not necessarily lead to greater understanding of the present.
  • Some participants challenge the idea that an increasing number of events (entropy) contributes to knowledge about the present, asserting that this may not be true.
  • There are claims that the wavefunction can be used to calculate probabilities of future states, but interactions must be accounted for, leading to updates in the wavefunction.
  • A later reply questions whether interactions along the way affect the eigenvalues of the wavefunction and whether they lead to new sets of eigenvalues.
  • Some participants mention the many-worlds interpretation, which posits that there is no collapse and everything evolves deterministically.

Areas of Agreement / Disagreement

The discussion features multiple competing views, particularly regarding the interpretation of wavefunction collapse, the implications of entropy, and the relationship between past knowledge and present understanding. No consensus is reached on these points.

Contextual Notes

Participants express uncertainty about the implications of wavefunction collapse and its relationship to knowledge accumulation, with some suggesting that the total number of events may not be increasing as previously thought. The discussion also highlights the dependence on different interpretations of quantum mechanics.

  • #31
ddd123 said:
What if you don't register it? A Stern-Gerlach apparatus can run even if no-one's looking. In that case I don't see any trace of that information anymore.
You may not see it but it is there, scrambled in a gazillion entangled microscopic changes in the apparatus and environment. You must distinguish between classical erasure which is just deleting (readable) data and quantum erasure which undoes *all* of the microscopic entanglements. This is why they do quantum erasure experiments with photons, photons don't interact with the environment very much so observations made with simple observers, *can*, with immense effort and care, be erased.
 
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  • #32
Hey guys new to this forum sorry for derailing the thread, but can some of you guys suggest any books or websites on this type of stuff or quantum physics in general. Trying to get my head around this stuff so layman's terms might help. Cheers
 
  • #33
lowkee said:
Hey guys new to this forum sorry for derailing the thread, but can some of you guys suggest any books or websites on this type of stuff or quantum physics in general. Trying to get my head around this stuff so layman's terms might help. Cheers
This *is* all in layman's terms!
Sorry, couldn't resist.
 
  • #34
bhobba said:
The universe doesn't collapse into anything because the universe can't be observed which would requre something outside the universe interacting with it that by the definition of the universe is impossible.

Even if we can't measure anything because there is nothing outside the universe to interact with it to cause a collapse to a particular value,... If all we have is the universal wave function, that would still allow calculation of possible eigenstates and their probabilities, right? The question is: do we have enough information to derive in theory a universal wave function? If not, what do we need?
 
  • #35
friend said:
Even if we can't measure anything because there is nothing outside the universe to interact with it to cause a collapse to a particular value,... If all we have is the universal wave function, that would still allow calculation of possible eigenstates and their probabilities, right?

The probabilities thus obtained would be meaningless.

Its an open question if the state of the universe is a valid concept.

Thanks
Bill
 
  • #36
bhobba said:
The probabilities thus obtained would be meaningless.

The whole point of physics is to gain confidence in where the universe is going.
 
  • #37
friend said:
The whole point of physics is to gain confidence in where the universe is going.

The whole point of physics is to understand the fundamental laws of nature.

So far the answer to that has been surprising - symmetry.

Thanks
Bill
 
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  • #38
bhobba said:
The probabilities thus obtained would be meaningless.
Its an open question if the state of the universe is a valid concept.
Open in the sense of depending on interpretation and thus inherently unanswerable, or open in the sense of subject to ongoing research which stands a reasonable chance of answering it before the insects take over ?
 
  • #39
Derek Potter said:
Open in the sense of depending on interpretation and thus inherently unanswerable, or open in the sense of subject to ongoing research which stands a reasonable chance of answering it before the insects take over ?

Open in the sense of if its a meaningful concept at all - and that has interpretive aspects (eg in that statistical interpretation state is a preparation procedure - what prepares the universe?)- but that will take us way off topic and requires another thread.

Thanks
Bill
 
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  • #40
What would it take to write the universal wave function? What do we need to write any wave function? we need the starting state, and then what...? The hamiltonian or lagrangian for each particle, and then what?
 
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  • #41
friend said:
What would it take to write the universal wave function? What do we need t write any wave function? we need the starting state, and then what...?

A model eg
http://www.superstringtheory.com/cosmo/cosmo41.html

Some question if such are meaningful.

Thanks
Bill
 
  • #42
bhobba said:
A model eg
http://www.superstringtheory.com/cosmo/cosmo41.html
Some question if such are meaningful.
I choose to interpret it as meaningful.
 
  • #43
According to William Thomson (Lord Kelvin) who predates Planck et al, entropy is always increasing implying that the total energy level will asymptotically approach some unspecified universal mean of total neutrality in some very distant future. Of course, Lord Kelvin was a Creationist (not the YEC type, though) who thought the Earth was only, say, 3-4 million years old.)
 
  • #44
stevmg said:
According to William Thomson (Lord Kelvin) who predates Planck et al, entropy is always increasing implying that the total energy level will asymptotically approach some unspecified universal mean of total neutrality in some very distant future.

There is this law called conservation of energy that means what you wrote above is incorrect. Its entropy that increases - chaos is coming - energy remains the same.

Thanks
Bill
 
  • #45
Friend said, "We are certain of the past but not sure of the future."

I'm not so sure that statement is true. When we talk about the collapse of a wave function, we're talking about what it is observed to be a a single point in time. However, the uncertainty of the result still exists in the past. If we see a photon go through the right slit now, our uncertainty of 5 minutes ago would still exist in the past. 5 minutes ago that collapse hasn't happened. However, if I return to the past of 5 minutes ago knowing which slit it will go through in 5 minutes, will the waveform collapse when I reach 5 minutes ago, or will it continue until we reach the future where we see it go through the right slit? And if it doesn't collapse when I reach 5 minutes ago, and this time goes through the left slit, have I caused a fork in the futures of the universe?

"t" looks so easy in an equation on paper.
 
  • #46
bhobba said:
Its entropy that increases - chaos is coming - energy remains the same.

Has entropy been proven on first principles of QM or GR?
 
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  • #48
friend said:
Has entropy been proven on first principles of QM or GR?

Actually, I meant: Can the 2nd law of thermodynamics be derived from first principles?
 
  • #49
friend said:
Actually, I meant: Can the 2nd law of thermodynamics be derived from first principles?

Yes - but the math is deep:
https://terrytao.wordpress.com/2008/01/30/254a-lecture-8-the-mean-ergodic-theorem/

The above is a very famous theorem. The trouble is it isn't quite general enough to fully provide the foundations to statistical physics. The key theorem required is still unproven:
http://library.lanl.gov/cgi-bin/getfile?00285754.pdf
http://www.pnas.org/content/112/7/1907.full.pdf

Thanks
Bill
 
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