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What is ad hoc inflation?


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#1 Becca

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Posted 30 June 2004 - 08:11 AM

I found a reference to an "ad hoc inflation field" in May 04's Scientific American. I tried to find out what it was on the net but without much success. can anyboy explain this to me in terms that i will understand? (I have just done a physics AS.)

#2 GAHD

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Posted 01 July 2004 - 12:21 PM

ok, I 'think' that it might be referring to the force causing the expansion and acceleration of the universe. I think I have that magazine too; is it the one with the mini article on viral computers, or the one with the mini article on remote/automated vehicles?

#3 Freethinker

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Posted 01 July 2004 - 01:55 PM

From what I could find, the "ad hoc" part is more a description of how mainstrean, supportable the propostion is, than a modifier of it.

#4 Bo

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Posted 01 July 2004 - 04:44 PM

hmm ok i'll try to explain this in simple language, but it's not a simple subject; please let me know if i need to clearify things more (i dont know what a physics AS is....) Posted Image ...
In modern cosmology there are many problems, but one very fundamental is the inflation problem. This basicly says that the universe these days is accelerating and most probably also was accelarating (very fast!) just after the big bang. One of the ideas (and most promising) to solve this problem is to introduce a scalar field which is in general called the inflaton field (Note that a field in Quantum field theory is basicly a distribution of (virtual) particles). This field couples to the metric (the structure of space-time) and is subject to some potential V (the potential basicly says how the field behaves). The problem now is to think of a good potential that discribes the observations well. These potentials are sometimes called 'ad hoc' because They're just made up with the thought 'well maybe this works!'

Some remarks: - A similar scalar structure is The higgs field that gives particles their mass. -The mass of the inflaton is approxamitly 10^12 GeV (for comparison: the higgs particle has a mass of about 200 GeV, a factor tenbillion less. -In string theory scalar fields like this arise quite naturally. As you might know string theory needs 10 space-time dimensions to work, but we 'see' only 4. But we can roll up these extra dimensions,so that they are negligeble. However this roling up gives rise to scalar fields that quite naturally couple to the metric.
Some references: http://www.biols.sus...ibbin/cosmo.htm (haven't read it, but it's called inflation for beginners and it does mention the scalar fields) http://nedwww.ipac.c...le/Liddle5.html]http://nedwww.ipac.caltech.edu/level5/Liddle/Liddle5.html]http://nedwww.ipac.caltech.edu/level5/Liddle/Liddle5.html[/L][/L] gives a nice overview. More advanced, but the first pages are also understandable by undergraduate readers is: http://arxiv.org/abs/hep-th/0402051 Bo

#5 Becca

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Posted 02 July 2004 - 03:43 AM

Thanks Bo that helped a lot. As is half an A level that means that i'm in first year at college and am 16 years old. I am also Engish.

#6 Bo

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Posted 02 July 2004 - 04:19 AM

so you skipped some classes or so? Have fun with the most beautifull study there is Posted Image (/promo remember: go for theoretical physics! /promo -Bo

#7 Truth

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Posted 02 July 2004 - 09:20 AM

Inflating rectangles or inflating away the imbalances in a rectangle.

#8 Freethinker

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Posted 02 July 2004 - 09:43 AM

Originally posted by: Bo
These potentials are sometimes called 'ad hoc' because They're just made up with the thought 'well maybe this works!'

Thanks Bo. That was what I was (very unsuccessfully) trying to say.

That rather than an "ad hoc Inflation" being a SPECIFIC KIND of "inflation", it is meant to suggest acceptance of concepts "for this" (the literal meaning of "ad hoc") particular theory of inflation as being currently discussed. Just like saying, "as a matter of convenience for this discussion we will accept...".