About the Expansion of the Universe

Mike Hewson
Mike Hewson
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RE: I think we prefer the

Message 95152 in response to message 95151

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I think we prefer the thermodynamic one only because it makes us feel more comfortable. It just fits us in the classical sense. I think we are going see a lot more weirdo theories probably some even peer reviewed (And hear is a cheer for them) before we can come up with experiments to contain this mess we call cosmology.


Yeah. It's more viscerally obvious, we film an egg falling and breaking. Run the frame sequence either way and it's quite an asymmetric choice. No doubt. Spilt milk etc ....

Cheers, Mike.

( edit ) Some other notable Russian firsts - first woman in space, first multi-crew spaceship, and also first unmanned probes to Earth, Venus & Mars!

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Ver Greeneyes
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I finished writing an

I finished writing an introductory paper to Cosmic Inflation yesterday (as an assignment for an interdisciplinary sciences class). I tried my best to keep the amount of technical detail to a minimum (so you won't drown in formulas) while still giving the reader a good idea of why we need inflation, and how it works. Would you guys be interested in reading it?

Mike Hewson
Mike Hewson
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RE: I finished writing an

Message 95154 in response to message 95153

Quote:
I finished writing an introductory paper to Cosmic Inflation yesterday (as an assignment for an interdisciplinary sciences class). I tried my best to keep the amount of technical detail to a minimum (so you won't drown in formulas) while still giving the reader a good idea of why we need inflation, and how it works. Would you guys be interested in reading it?


Absolutely! :-)

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Ver Greeneyes
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RE: Absolutely!

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Absolutely! :-)

Cheers, Mike.


Here you go. :)

I imagine at least some of you already know a lot more than I do.. this isn't exactly a peer-reviewed paper or anything, so if any experts read it, don't be too harsh on me for any mistakes I might have made. But if I -did- make any mistakes, I'd love to hear about them.

Mike Hewson
Mike Hewson
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RE: I imagine at least some

Message 95156 in response to message 95155

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I imagine at least some of you already know a lot more than I do.. this isn't exactly a peer-reviewed paper or anything, so if any experts read it, don't be too harsh on me for any mistakes I might have made. But if I -did- make any mistakes, I'd love to hear about them.


Within the obvious limits of brevity, you've done quite well. It's one of those areas where each word could take a chapter to define accurately. You've seized the basic idea that, not-with-standing some cosmic fluke, some underlying mechanism has produced uniformity where there otherwise ought not be any. I'm not aware of any simpler hypothesis regarding horizons. The 'slow roll' bit is the inflationary expansion, the 'fast roll' is the entropy production ( particles/heat ) sliding into the Big Bang proper where the various forces 'freeze out' as the temperature falls. This gives the baryogenesis and the matter over anti-matter ( see Sakharov criteria ) asymmetry with about a billion photons per baryon.

I'm not aware of the specific variant you have described, but that's OK. I guess with, say the Planck mission, there may be opportunity to decide amongst them.

Correction re Twin's Paradox : one can describe accelerations of objects within a non-accelerated frame ie. look at accelerating particles with SR. The asymmetry remains however b/w the twins. So you don't need to invoke GR, as I'd asserted before. So one could compare world lines of each twin in an inertial frame and note that the stay-at-home twin has the greater proper time ( time as measured by an observer along the world line ), with the traveling twin having a lesser proper time elapse. And less so with a faster speed. In the extreme a photon bouncing out and back has no elapsed proper time.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Ver Greeneyes
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RE: The 'slow roll' bit is

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The 'slow roll' bit is the inflationary expansion, the 'fast roll' is the entropy production ( particles/heat ) sliding into the Big Bang proper where the various forces 'freeze out' as the temperature falls.


Actually, the 'fast roll' stage is proposed in the 2009 paper I used as my source (guess I should have made sure to reference them there). It's a stage that happens -before- the slow roll stage, as far as I could tell, but for the specifics you'd have to check their paper. The entropy production can be divided into a 'preheating' stage that is caused by fluctuations around the minimum potential energy of inflaton (caused by the oscillating nature of its evolution function, if I understood them correctly), and a 'reheating' stage that is inflation decaying into radiation and particles (but I don't understand the details well enough to do much more than paraphrase them in my paper), and which actually cuts off inflation altogether.

Either way, I'm glad you think I did a good job - you're the first person with any technical knowledge to read it so far!

Mike Hewson
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RE: RE: The 'slow roll'

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Quote:
The 'slow roll' bit is the inflationary expansion, the 'fast roll' is the entropy production ( particles/heat ) sliding into the Big Bang proper where the various forces 'freeze out' as the temperature falls.

Actually, the 'fast roll' stage is proposed in the 2009 paper I used as my source (guess I should have made sure to reference them there). It's a stage that happens -before- the slow roll stage, as far as I could tell, but for the specifics you'd have to check their paper. The entropy production can be divided into a 'preheating' stage that is caused by fluctuations around the minimum potential energy of inflaton (caused by the oscillating nature of its evolution function, if I understood them correctly), and a 'reheating' stage that is inflation decaying into radiation and particles (but I don't understand the details well enough to do much more than paraphrase them in my paper), and which actually cuts off inflation altogether.


Well, there you go! The lecture I watched ( circa 2003 ) put the slow roll before the fast ( or I've remembered it wrong ), so I guess they are fiddling with the in and outs of the detail. Another good reference is SLAC Summer Institute, of which you can stream all the talks. But of course be aware of which year one is sourcing.

Quote:
Either way, I'm glad you think I did a good job - you're the first person with any technical knowledge to read it so far!


The idea of inflation theories is to 'deliver' the Universe to a point where the 'normal' hot big bang scenario takes over. So in addition to solving the horizon issue, the other known characteristics must be covered too. I find it a bit of a boggle the time markers used for this description - numbers like 10^(-35) of a second, say! :-)

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Ver Greeneyes
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RE: I find it a bit of a

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I find it a bit of a boggle the time markers used for this description - numbers like 10^(-35) of a second, say! :-)


As if the sheer spatial expansion wasn't enough :) (inflation for 64 efolds = expansion by a factor of ~10^28)

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