i'm sure you've all noticed that photons are everywhere. they have momentum (see discussion elsewhere in this halfbakery about GRAVITY TIME MIRRORS) and therefore can exert pressure. p.n. lebedev calculated, in 1910, that the pressure of sunlight at earth orbit is 4.7x10^-6N/m^2, and jack vance in 1962 simplified the numbers a bit to about an ounce per acre.

not much. but it is always there, and always pushing (until the sun goes out some billions of years from now). nasa and jpl, along with space agencies from russia and japan, at least, have spacecraft and mission designs that take profound and surprising advantage of this fact.

an observation, there are a LOT of acres in a virtual spherical shell at earth's orbital distance from the sun. and, there are a LOT of stars out there, each one putting out a LOT of what i will call "photon gas pressure".

"gas", because photons are everywhere, and everywhere moving in every direction. and exerting pressure in every direction. and they have been doing it for 13.7 billion years or so. at first, gravity dominated a slowdown of the universal expansion; but it appears that the expansion has been speeding up over the last five or so billion years, prompting some astronomers to re-posit einstein's cosmological constant to explain the acceleration.

surely you can see that i am halfbaking a physical mechanism to explain the apparent acceleration. thoughts?
-- spike, Oct 12 2007

Well, I have trawled through enough "solar sail" stuff to Know that I am underqualified (strike under/replace with un) to comment. But,..........

I think I sorta see where you are coming from, not so much an invention as proposal for spike's universally repulsive photon theory?

In an (unbound system?) like the universe you would think that with action having reaction, force on everything would tend toward expansion?

'Spose you could be onto something.

<goes out on limb>[+]
-- the dog's breakfast, Oct 12 2007


An old concept: Eddington limit--the point at which photon pressure exceeds the gravitational attraction of a light-emitting body.
-- ldischler, Oct 12 2007


If spike's supposings were something to savour, surely the gravitational force by The Sun on The Earth would be overcome by the photon pressure? Fortunately, it isn't.
-- Ling, Oct 12 2007


I got it. Photons work at a distance. They do not decrease in punch with distance.
-- bungston, Oct 12 2007


//i'm sure you've all noticed that photons are everywhere/
<turns light out, closes eyes> Nope. </tlo,ce>
-- AbsintheWithoutLeave, Oct 12 2007


This is true, photons do have a momentum, and hence the number of photons hitting per area per second is a form of dynamic pressure.... photons do play a small part in the expansion of the universe, but to the best of my knowledge, photons alone don't quite account for the observed redshift of all the stars and galaxies.
-- quantum_flux, Oct 12 2007


//can exert pressure. p.n. lebedev calculated// There are times when the affectation of not using capitals just makes things harder to read. But I digress.

If I understand, you're saying that photons are pushing things apart, hence accounting for the apparent accelerated expansion of the universe? Well, OK, maybe. But I would have expected that someone somewhere would have already factored this in to their calculations. I mean, photon pressure is well known, no?

Anyway, if we wait another 10 years the problem will be all different again. Every 10 years we discover that what we thought we knew about the universe only accounts for 10 percent of what there actually is. So, if I were you, I'd just ride this one out.
-- MaxwellBuchanan, Oct 12 2007


Stop the money waste! Cancel the LHC! Take your Higgs boson and shove it. <Caveat venditor> this might come back to haunt me in ten years time </cv>.
-- 4whom, Oct 13 2007


HEY ALL! (just kidding)

thanks for the feedback. perhaps i should hit up the astronomy group as well as the other:light folks.

idischler, thanks for the mention of the eddington limit, will research.

ling, see idischler's note, and bungston's below. i don't (yet) even know how to figure where edd's limit is in our solar case, but i'm guessing it's going to be pretty far away, much farther than our earth orbit. my best guess is at least a galactic scale, probably intergalactic.

absinthe, not all photons are visual light. indeed, most may be, probably are, infrared, which we can't "see" unless, e.g. it's a warm, sunny day. even the warmth of the inside of your closed eyes puts out some photons. not as much as the sun or even a candle, but some. and no doubt "<tlo,ce>" means something, but i remain in the dark (so to speak).

maxb, "someone, somewhere" may have, but i haven't heard of it. not that i've done a lot of research, just a lot of looking at stars, and wondering what the heck is going on out there, and where we fit in, etc. "ride this one out"? mmm, no thanks.

but again, thanks all. i don't think i have THE answer to the apparent "acceleration" of the expanding universe. indeed, as i read it, the current expansion is only a little less slowed than it would be if only gravity were affecting it. the acceleration is subtle, but if it keeps up, and keeps increasing, as seems to be the case, the universe of billions or trillions of years in the future will be a much lonelier place than it is now. why am i concerned? good question. it IS only a half-baked idea.
-- spike, Oct 15 2007


//and no doubt "<tlo,ce>" means something//
sp. "</tlo,ce>"
-- AbsintheWithoutLeave, Oct 15 2007



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