19 Aug 2007 14:27:43 UTC

Topic 193056

(moderation:

Hey all smart people

At any point in space you will see several sources of light. Not just light but lots of different wavelengths of the electromagnetic spectrum (and cosmic rays, neutrinos and all kinds of other weird particles as well). Does this not mean that every single point in space is occupied by photons, and space is therefor made of solid photon?

If every point of space is occupied by particles, all which have a mass, albeit a small one, would this not add up to en enormous mass, big enough to collapse the whole universe?

I'm probably missing something important in this argument, but it's something I've been pondering upon.

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## is space made of solid photon?

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Photons don't have a rest mass, and neutrinos have a very small one, if any. There was a paradox, called Olbers' paradox, which said more or less: if the universe is infinite, why the sky is not always bright, due to the infinite numbers of stars contained in it? The more common answer is that the universe is finite.

Tullio

## Or could it be that all the

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Or could it be that all the intervening gas and dust diffuse, absorb and reflect back some of the light?

Also check out this months issue of Astronomy Magazine. What lurks between galaxies?

me-[at]-rescam.org

## this is diferent from Oblers

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this is diferent from Oblers paradox, because anywhere in space, you WILL in fact see light, and therefor photons are occupying that space(?)

## I believe that you are right

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I believe that you are right in the assumption that in every point in space you would be able to detect a photon, not necessarily in the visual spectra but a photon anyway. The question is...

Does that mean that you can define a amount of energy in that point or does it demand that the photon interact with something at that point?

## Since the photons (neutrinos,

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Since the photons (neutrinos, etc) are zipping along, and since photon (neutrino, etc) detectors cannot be shrunk to an arbitrarily small size (much less 'a point'), maybe it makes sense to ask more realistic questions, such as "how many {insert quantitative qualifiers here} photons (neutrinos etc) pass through a transparent sphere (way out in the depths of the BoÃ¶tes Void), of radius 1 m, every second?"

## RE: At any point in space

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Is is proper to characterize space from only one type of the many bits and pieces found in space? The vacuum energy is mathematically infinite, when naively calculated, and even with regularization and renormalization, the canceling of one infinite quantity, by subtracting another infinite quantity from it, is still rather, well, it's iffy*... maybe best to say that space is â€œpotential [anything/everything]â€?...?

Would it? What about the enormous distances between all that mass? What about velocities of the mass? What about the expansion of space itself? How many other variables to consider?

*There are an infinite number of integers (the whole numbers we count with). Half of them are odd (1, 3, 5, 7, ...) and half of them are even (2, 4, 6, 8, ...). So in which set of numbers are there more elements? An equal amount of odds and evens, to be sure, but are there twice as many numbers in the set of integers as there are in the set of odds (or evens)? Nope, each set still has an infinite number of elements! Go figger.... :)

## RE: *There are an infinite

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Chipper, I am not a mathematician, but from my studies of long time ago I remember that there is a whole range of infinities, starting perhaps from Aleph-null (?).

Tullio

## RE: What about the enormous

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That's my point. there are no enormous distances between all this mass, because even in intergalactic space, in every inch of it, you will find particles, and their speed doesn't matter, as it is a continuous flow.

I'm afraid I don't understand most of you're reasonings, probably because I've never studied physics.

Nereid made me realize however (if i understood him correctly..), that detecting a photon just means it hit somewhere within the volume of the detector, so detecting several at once does not mean they are occupying the same area of space, so there can be plenty of space between them. how silly of me...

a friend of mine also pointed out that neutrinos in fact are a candidate for dark matter...

## I believe that I have read

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I believe that I have read that light can be described both as an electromagnetic wave or as a particle but that does not mean that light actually ARE a wave or a particle, it's just behave like that. One guy write as an example that he had a son that could swim like a fish and clime like a monkey but that his son was neither of those animals, he just behaved like that :). Does a photon have a volume and if so does photons with different energy have different volume?

## RE: RE: *There are an

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Yes, the Aleph numbers, representing the cardinality of infinite sets, introduced with set theory by Georg Cantor, along with notions like 'infinity of infinities' and one set with an infinite number of elements can still be 'more numerous' than another set with also an infinite number of (different) elements. Cantor realized that infinite sets can have different cardinalities. I'm not a mathematician either, but have an affinity for the set of prime numbers, whose cardinality is also Aleph-null...

As it pertains to agge's question about the composition of space, I was trying to point out that there's a way to use quantum mechanics to compute an 'expectation value' for the energy in vacuum. But you have to sum over all the points in space and that gives an answer of infinity. And then there's the question of how many dimensions there are to space (or spacetime)... so what's the cardinality for all that, is it really Aleph-null? Anyway, there's also a number available from the cosmologists regarding the total number of photons that were created since the big bang... of course the photons are all distributed in space, and not all packed into any one region of it. But I was mainly trying to point out that space contains more than photons, and the question of whether the universe will collapse or not is a good one, and still an open one, and the effort to answer it has many variables, in addition to the photons, that have to be considered... To me, one of the most interesting questions about space is what structure does it have, that it is warped by gravity?