Neutrinos and the expansion of the Universe.

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MarshyMarsh
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Neutrinos and the expansion of the Universe.

Postby MarshyMarsh » Thu Feb 12, 2009 5:52 pm UTC

With the recent discovery of the Neutrino, I just began to question how we now evaluate the size of the Universe, now we can guesstimate the size of the visible Universe fairly easily, but if these little particles have been firing off in all directions for a fairly long time the Universe in terms of originating mass must have a far larger (I use the term lightly here) Area than we would have guessed before the discovery of the Neutrino. I mean travelling at near the speed of light with no need for a medium to travel through, surely the Universe must be even more uncomprehensably huger than we where unable to comprehend before (I suppose in terms of comprehension if doesn't matter).

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Re: Neutrinos and the expansion of the Universe.

Postby alexh123456789 » Thu Feb 12, 2009 6:08 pm UTC

IANOP but I don't thinkthat the mass of the universe is related to it's size. Also, neutrinos are very very light so probably don't factor in that much (not sure if there's a ton of neutrinos though). I think the size of the universe is absolute (or the age) because of time dialation and length contraction and all that stuff.

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Re: Neutrinos and the expansion of the Universe.

Postby Xanthir » Thu Feb 12, 2009 7:04 pm UTC

MarshyMarsh wrote:With the recent discovery of the Neutrino, I just began to question how we now evaluate the size of the Universe, now we can guesstimate the size of the visible Universe fairly easily, but if these little particles have been firing off in all directions for a fairly long time the Universe in terms of originating mass must have a far larger (I use the term lightly here) Area than we would have guessed before the discovery of the Neutrino. I mean travelling at near the speed of light with no need for a medium to travel through, surely the Universe must be even more uncomprehensably huger than we where unable to comprehend before (I suppose in terms of comprehension if doesn't matter).

You must be somewhat confused. Neutrinos were first theorized in 1930, and discovered experimentally in 1942. That certainly doesn't qualify as "recent".

As well, just how large do you believe we thought the universe was? *Photons* travel faster than neutrinos, so by your (invalid, more on this later) argument, the discovery of the neutrino wouldn't have expanded the hypothesized size of the universe at all. Specifically, we would have already assumed that the universe has a radius of roughly 15 billion light years.

In reality, the universe is much larger than that, because universal expansion causes things to retreat from us faster than the speed of light.
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Re: Neutrinos and the expansion of the Universe.

Postby thoughtfully » Thu Feb 12, 2009 8:01 pm UTC

What is a recent discovery is that neutrinos have mass, and therefore contribute to the dark, non-baryonic mass of the Universe. It's not enough, however.
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Re: Neutrinos and the expansion of the Universe.

Postby doogly » Thu Feb 12, 2009 8:29 pm UTC

And if anything, the mass would serve to make the universe more closed.
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Re: Neutrinos and the expansion of the Universe.

Postby thoughtfully » Thu Feb 12, 2009 8:38 pm UTC

It's not so much that they make the Universe heavier; rather, they account for some of the "missing mass" that we already knew about.
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Re: Neutrinos and the expansion of the Universe.

Postby Matterwave1 » Thu Feb 12, 2009 8:51 pm UTC

thoughtfully wrote:What is a recent discovery is that neutrinos have mass, and therefore contribute to the dark, non-baryonic mass of the Universe. It's not enough, however.


Really? Can you cite an article for this? Pretty interesting stuff. :)

Last I heard, we had a upper bound on the mass of the neutrino but no lower bound...

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Re: Neutrinos and the expansion of the Universe.

Postby thoughtfully » Thu Feb 12, 2009 8:57 pm UTC

Maybe no lower bound, but it's known to be greater than zero. This is a consequence of oscillations, which were strongly indicated with the missing solar flux, and later observed directly with the MINOS experiment.

Googling "neutrino mass" suggests there may be a lower bound, depending on what data you are citing, and which neutrino.
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Re: Neutrinos and the expansion of the Universe.

Postby MarshyMarsh » Fri Feb 13, 2009 5:38 pm UTC

Bit of a late reply to this, To clarify, I should of memtioned the discovery of Neutrinos having mass (meaning they travel slightly less than the speed of light). Since a Neutrino has a mass >0 a large amount would contribute to a large mass, given that these do not need a substance to travel through (wave partical duality) then they are expanding the size (geometric, again I understand this is a poor way of looking at the Universe) of the Universe. Photons have a rest mass of 0 (I am unsure if Neutrinos also have a rest mass of zero, I am pretty sure they are not as they oscillate, a Photons mass comes ffrom its energy), but as far as an object which has mass the Neutrino must count towards the size of the Universe. In mass/distance.

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Re: Neutrinos and the expansion of the Universe.

Postby parallax » Fri Feb 13, 2009 5:47 pm UTC

I think what you're saying is, given a fixed density for the universe, any additional mass must increase the size of the universe. I think we have calculated the size of the universe independently of its mass or density. In fact, our calculation of the universes size was too large to account for its density given the amount of mass we were able to see. Thus, we suggested that there must be "dark matter", which is matter that we can't see very well, to make up the difference. Neutrinos make up a small percentage of that dark matter.
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Re: Neutrinos and the expansion of the Universe.

Postby thoughtfully » Fri Feb 13, 2009 7:25 pm UTC

We have a pretty good idea of the size of the observable Universe, since that is fixed by its age times the speed of light. But, nobody really knows the full size, that really depends on how the rate of expansion has changed over time.

For instance, during inflation, any point in the cosmic fireball would have been blown utterly away from being "causally connected" with most of the rest of the initial matter in the big bang, and because of this, we can expect that the observable universe is actually very small in comparison to the whole.
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Re: Neutrinos and the expansion of the Universe.

Postby doogly » Fri Feb 13, 2009 9:17 pm UTC

thoughtfully wrote:We have a pretty good idea of the size of the observable Universe, since that is fixed by its age times the speed of light.


Not actually true! This would only be true in flat, non expanding space. What you want to mean by distance isn't even that well defined, which I discussed a bit here viewtopic.php?f=18&t=31806&p=1158478& before.

But yes, definitely, much more non causally connected universe outside of ours.
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