Arcadian Functor

occasional meanderings in physics' brave new world

My Photo
Location: New Zealand

Marni D. Sheppeard

Sunday, May 31, 2009


Although I will have four wonderful months over the summer to focus on work, I am naturally wondering where I should go when my UK visa runs out in October. Should I hide in a Perimeter cupboard? Having seen homeless people in Toronto in winter, I suspect that would not be a great option. Maybe I could head to Switzerland once again, and hopefully this time avoid that nasty crevasse on the upper Grosseraletsch glacier. Camping out at altitude is free there, but internet connections might be problematic. Hmm. New Zealand is looking quite appealing compared to the current alternatives.


Anonymous Anonymous said...

Perhaps if you actually do some work and get a few published papers, you can get a position somewhere else.

May 31, 2009 12:30 PM  
Blogger Kea said...

Gee, what original advice. Let's see, I've heard that about once a day for over 20 years. Heh, do you think just maybe that I might actually care more about the physics than my job prospects?

June 01, 2009 12:07 AM  
Blogger L. Riofrio said...

You would be welcome in CA or Texas. In the former you would be one train ride from either Berkeley or Stanford. In Texas there are wide open spaces and a waterfront view. If I were not a scientist I would like to work as a guide in the Space Center--theyt wear blue suits just like the astronauts.

June 01, 2009 4:00 AM  
Anonymous Anonymous said...

No, what's clear to me is that you are a person who likes to talk about physics and pretend to be a physicist, but who actually doesn't really ever accomplish anything.

June 01, 2009 12:25 PM  
Blogger L. Riofrio said...

What nasty things anonymous says! Kea has earned a PhD and a position at Oxford.

It is sad that other anonymous cowards are in charge at British Immigration. They try to keep a few examples out while otherwise allowing unlimited immigration, letting the wrong people in.

June 01, 2009 2:17 PM  
Anonymous Tony Smith said...

ttackers who hide behind Anonymity clearly show that their obvious low self-esteem is in fact well deserved.

On another matter, probably off-topic but maybe hopefully leading to fun discussion: Kea, your blog page says:

"... If you could peer far enough into the night sky, you'd see a star in any direction you looked. ...".

Wouldn't that be a violation of the Olbers Paradox?

As John Baez says on his web site Physics FAQ, based on material by Scott I. Chase:

"... With infinitely many stars, every element of the sky background should have a star, and the entire heavens should be at least as bright as an average star like the Sun. ...
The fact that the night sky is not as bright as the Sun is called Olbers' paradox. ...".

Tony Smith

June 01, 2009 4:47 PM  
Anonymous Tony Smith said...

Sorry for multiple posts due to my incompetence in clicking on blog comment stuff.

Also, the first word in them should be


Tony Smith

June 01, 2009 4:51 PM  
Blogger Kea said...

Problem fixed, Tony, and thanks Louise. Of course, we must acknowledge that the anonymous coward has a point, and I am rather hopeless at publishing papers. I am trying.

June 01, 2009 11:20 PM  
Blogger Kea said...

Re Olbers: dammit, Tony, I went through a long list of questions to find that one!

June 01, 2009 11:23 PM  
Blogger nige said...

Re: Oblers' paradox

It's the redshift that makes the sky dark. Professor Edward Harrison in his book Cosmology 2nd edition (Cambridge University Press, 2000) claims falsely on p505 that redshift can't explain the darkness because in a decelerating universe it causes too little loss of photon energy, but he is falsely comparing a decelerating big bang which does have redshift (since 1998 it has been known that the universe isn't decelerating) with an infinite static universe, where the correct comparison to ascertain the effect of redshift would be to compare the big bang with redshift to the big bang without redshift. Once you do the right comparison, Harrison's objections to redshift as a solution to Obler's paradox are removed. Redshift stops us being fried by the CBR which would be lethal infrared radiation with a blackbody radiation spectrum of 3000 K in the absence of redshift, but is only 2.7 K with redshift included. Thank God for redshift! (I've got a long essay I wrote about Harrison's quackery for my cosmology course at university many years ago which I've summarized on my blog, linked here.)

June 01, 2009 11:24 PM  
Blogger nige said...

Ummm. As the universe expands, the mass density falls as the inverse cube of the scale factor or effective radius (in a flat universe with no classical 'curvature'), R, i.e. mass density ~ R^{-3}. This is simply because the volume of a sphere is proportional to R^3 while the mass is conserved, so the density ~ mass/volume ~ 1/R^3.

But the energy density of the CBR of course varies faster, as ~R^{-4}, where the -4 exponent comes from the redshift which decreases the energy of photons (they are effectively 'stretched out' in length by redshift as the universe expands, so the frequency i.e. number of oscillations per photon per second as it is received, falls as the universe expands, reducing the energy by Planck's formula E = hf).

Now the funny thing is that we can use this energy density (Joules/m^3) ~ 1/R^4 relationship to work out how the CBR energy density fell with time since the CBR was emitted at 400,000 years after the BB. Since the large scale universe is flat, the scale factor R increased by a factor of 13,700,000,000/400,000 = 34,000 since the CBR was emitted.

Hence the energy density of the CBR is now (34,000)^4 = 10^18 times smaller than it was at 400,000 years after the BB when the CBR was emitted. This is why we're not being friend by the CBR.

However, it poses a question! Why is the energy density proportional to R^{-4}? Surely the CBR is converging inward, towards us, from a great distance, not diverging outwards from us! I think that there is a glib mathematical assumption being made here by the mainstream, which may or may not be right. Even if 1/R^4 is 100% right for energy density, there should be an effort to explain the mechanism by which the non-redshift part (i.e. the R^{-3} part of the total R^{-4} energy density fall) occurs. This is of interest to my work on quantum gravity exchange radiation. It's horrible how little mainstream cosmology work is founded on well-defended physical facts! It's all back-of-the-envelope guesswork which is now unquestionable dogma.

June 02, 2009 3:44 AM  
Blogger CarlBrannen said...

It's a combination of red shift and the fact that the universe has existed for only a finite length of time. So there is a horizon limit to how far you can look. (And then you see the CMB.)

June 02, 2009 4:43 PM  
Blogger Mitchell said...

Marni would easily get a fellowship at the Boundary Foundation, the antipodean rival to the Perimeter Institute, if it actually existed.

June 02, 2009 6:38 PM  
Blogger nige said...

Hi Carl,

In that case, what's to stop you seeing radiation from the first microsecond of the big bang?

The CBR masks it because it's even more redshifted than the CBR!!

The density and temperature of the universe increases without known limit as you look back to 13,700 million light years distances, or 13,700 million light years ago (time).

There's nothing to stop you seeing primeval radiation from arbitrarily short times after the big bang, apart from redshift.

So I disagree that the distance limit is any solution, you need to remember that as you look back to distances approaching time zero, the intensity of the light goes towards infinity. This big bang scenario is nothing to do with the steady state lookback limit. The question why the sky is dark can't be answered using a false analogy such as the steady state universe. You have to take the big bang model, and explain why you can't see radiation from near time zero. It's masked by the CBR because it's so redshifted it's undetectable. So redshift is the only answer, as far as I can tell.

June 03, 2009 1:59 AM  
Blogger CarlBrannen said...

nige, I think your logic is right for the big bang scenario, but I don't believe in the big bang.

I think the universe is flat as a board and always has been. In my world, it's the gravitons that make the universe appear expanding on long distances, and lumpy on short distances.

June 04, 2009 5:37 PM  
Blogger nige said...

Hi Carl,

'... I don't believe in the big bang.'

That's good, because science isn't about beliefs or religion. Redshift does appear to suggest expansion (because no other proven mechanism for the uniform shifting of line spectra has ever been found), the ratio of hydrogen to helium abundance suggests fusion at high temperatures in an expanding universe, and the CBR suggests the emission of radiation when the universe became transparent as radiation-absorbing ions combined with electrons to become transparent hydrogen gas at about 4000 K temperature. What I want to see is some proof that the CBR radiation energy density should fall as time^{-4}. The hand-waving proof usually given that the energy density should fall as t^-1 due to redshift is OK, but the claim that expansion should cause an additional t^-3 fall due to volume expansion ignores the geometry in which the CBR is converging inwards towards us from a spherical shell nearly 13,700 million light years distant. This is not spherical divergence. You'd expect converging radiation energy density to increase, not fall! I think t^{-4} may be right but the full explanation is not the arm-waving claim usually made.

'In my world, it's the gravitons that make the universe appear expanding on long distances, and lumpy on short distances.'

Spin-1 gravitons would do just that! Immense masses over large distances (clusters of galaxies, superclusters, etc) exchanging spin-1 gravitons will push one another apart, like the dough pressure pushing raisins apart in a baking cake. For smaller masses and distances, the inward pressure on all sides of spin-1 graviton exchange from clusters of galaxies predominates over the repulsive exchange that occurs literally between any two small masses, so they get pushed together. Gravity.

June 07, 2009 8:53 AM  

Post a Comment

<< Home