Assumptions of Hawking-Penrose 1970 Singularity Theorem

  • Context: Graduate 
  • Thread starter Thread starter Cerenkov
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Discussion Overview

The discussion revolves around the assumptions underlying the Hawking-Penrose Singularity Theorem from 1970. Participants explore the validity of these assumptions in light of contemporary findings and their implications for the theorem's applicability, particularly concerning dark energy and inflation.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant lists five assumptions they believe were made in the theorem, including the universe being like a Friedmann model, infinitely large, expanding fast enough to avoid re-collapse, the correctness of general relativity, and containing observed amounts of matter.
  • Another participant challenges the first three assumptions, stating they were not part of the 1970 theorem, while confirming the correctness of the assumption regarding general relativity.
  • It is noted that the assumptions related to matter-energy content require the universe to be dominated by ordinary matter and/or radiation to satisfy energy conditions.
  • Dark energy is discussed as not satisfying the energy conditions, which raises questions about the theorem's applicability to a dark energy dominated universe.
  • Inflation is mentioned as also violating energy conditions, making the theorem inapplicable to most inflation models.
  • Questions are raised about whether the singularity theorem could apply to the universe at certain times when it was not dark energy dominated.
  • Participants express a desire for clarification on how inflation violates energy conditions and which specific conditions are involved.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the validity of the assumptions listed, with some affirming certain assumptions and others disputing them. The discussion remains unresolved regarding the implications of dark energy and inflation on the singularity theorem.

Contextual Notes

There are limitations in the discussion regarding the assumptions made in earlier papers by Hawking and Penrose compared to the 1970 theorem, as well as the implications of dark energy and inflation on the theorem's applicability.

  • #31
Cerenkov said:
With all due respect Peter, I did not make the term semiclassical up.
You did as far as mathematical theorems are concerned. None of your references use the term that way. They all use the term as a way of describing models that are used in physics, not mathematical theorems.
 
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  • #32
PeterDonis said:
You did as far as mathematical theorems are concerned. None of your references use the term that way. They all use the term as a way of describing models that are used in physics, not mathematical theorems.

Now that you've clarified things I can what you mean.

But your statement, ' Nobody in the literature actually uses them' was insufficiently clear.

If you had written, 'Nobody in the literature actually uses them THE WAY YOU DO', that would have been clearer.

Had you done that then I would have simply accepted your expertise and then asked you what the proper way of using these terms was.


But I can now see that my one question about the BGV is the result of incorrect understanding on my part.

So I thank you for your help Peter and I have no further questions.


Cerenkov.
 
  • #33
Cerenkov said:
your statement, ' Nobody in the literature actually uses them' was insufficiently clear.

If you had written, 'Nobody in the literature actually uses them THE WAY YOU DO', that would have been clearer.
Here is what I said:

PeterDonis said:
"Purely classical" and "semi-classical" regarding theorems are just terms you made up. Nobody in the literature actually uses them.
Note the bolded text, which is crucial.
 
  • #34
Yes, that's not in dispute here, Peter. Thanks to your guidance I now see what I did.

The issue is how you corrected me.

Technically you are 100% correct. I did 'make up' things in the way you pointed out.

But that is not the be all and end all of the issue.

You are the tutor and I am the student - but we are both human beings and respect is a two-way street.

Therefore, respectfully, I submit that you telling me, albeit in a technically correct way, that I'm making things up, was perhaps not the best way of handling the point on a person-to-person level.

Can you at least meet me halfway on this?


Thank you,

Cerenkov.
 
  • #35
Cerenkov said:
Thanks to your guidance I now see what I did.
Ok, good.

Cerenkov said:
I submit that you telling me, albeit in a technically correct way, that I'm making things up, was perhaps not the best way of handling the point on a person-to-person level.
I'll try to keep that in mind for the future.
 
  • #36
Once again, thank you for your help, your guidance and your instruction, Peter.

I really appreciate the time and effort you've put in to help me along.

All the best,

Cerenkov.
 

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