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Author Topic: What is the mass of the cosmic microwave background radiation (CMBR)?  (Read 8061 times)

Offline syhprum

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Energy and mass being two faces of the same thing it should be possible to compute the mass equivalent of the CMBR that suffuses the whole of the observable universe.
I would be interested to know how this compares with the mass of all the observable matter.



MOD EDIT - PLEASE PHRASE YOUR POST TITLES AS QUESTIONS, IN LINE WITH FORUM POLICY. THANKS. CHRIS]
« Last Edit: 26/09/2009 12:23:12 by chris »


 

Offline lightarrow

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Energy and mass being two faces of the same thing it should be possible to compute the mass equivalent of the CMBR that suffuses the whole of the observable universe.
I would be interested to know how this compares with the mass of all the observable matter.
Sometimes ago I tried a very very very approximated computation and I found a number very small (even if not negligible) compared to the visible matter mass. Don't know if it's correct.
 

Offline that mad man

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Quote from the The Physics Factbook, a fair use website. [8D]

http://hypertextbook.com/facts/2004/HeatherFriedberg.shtml

"For your information: there are about 412 cmB photons per cubic cm (with an uncertainty of about 1); the energy density is the equivalent of 0.261 electron Volts per cubic cm (again uncertain by about +/-1 in the last decimal place); the equivalent mass density is 4.66 × 10-31 kilogrammes per cubic metre."

It maybe helpful if you can do the maths, unfortunately I cant. [:I]
 

Offline Mr. Scientist

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Quote from the The Physics Factbook, a fair use website. [8D]

http://hypertextbook.com/facts/2004/HeatherFriedberg.shtml

"For your information: there are about 412 cmB photons per cubic cm (with an uncertainty of about 1); the energy density is the equivalent of 0.261 electron Volts per cubic cm (again uncertain by about +/-1 in the last decimal place); the equivalent mass density is 4.66 × 10-31 kilogrammes per cubic metre."

It maybe helpful if you can do the maths, unfortunately I cant. [:I]

Yes, there is a lot of tricky uncertainty in there, but ultimately, the universe has around 10^120 magnitudes of energy than it should have. If that's interesting, you should read into th ZPE field.
 

Offline syhprum

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As Lightarrow says it is a very small figure (2.46*10^16 Kg) compared to the mass of the observable objects

Acknowlegments to 'Mad Man'

 Quote from the Pysics fact book
"The calculated mass of the universe ranges anywhere from 10^53 kg to 10^60 kg"
« Last Edit: 26/09/2009 10:26:19 by syhprum »
 

Offline JimBob

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Physics for Dummies 101 Question - Dark Matter

OK, now that I feel a little more safe asking rather simple questions, how can we know the mass of the universe if most is not seen and it's properties are only inferred because we do not have a proper way of observing or describing it. As far as I can tell it has no defined properties.

If it cannot even be defined, how then can the total mass of the universe be calculated?

 

Offline Geezer

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Physics for Dummies 101 Question - Dark Matter

OK, now that I feel a little more safe asking rather simple questions, how can we know the mass of the universe if most is not seen and it's properties are only inferred because we do not have a proper way of observing or describing it. As far as I can tell it has no defined properties.

If it cannot even be defined, how then can the total mass of the universe be calculated?



I'll take a shot at an answer  :D

When we monitor the behaviour of all the "stuff" in the universe we are able to observe, it does not behave as we would expect it to based on our current understanding of gravity and the nature of space.

Assuming our understanding of gravity and the nature of space is correct, we infer that there must be a large amount of invisible matter (dark matter) to produce the gravitational effects that we observe. Also, because we observe that the distant material in the universe appears to be accelerating away from us, we infer that some unknown force is producing this acceleration (dark energy).

Anyway, the total mass is determined from our observations of the gravitational interactions between objects in space. To make this work, we also have to assume that there is nothing "special" about our little part of the universe, and there is no evidence to suggest that there is.

Of course, if it turns out that our understanding of gravity and the nature of space is slightly wonky, we would have to revise our estimates of the total mass, and all bets regarding dark matter and dark energy would be off.

« Last Edit: 26/09/2009 20:25:53 by Geezer »
 

Offline JimBob

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I guess I  was asking if there is any direct evidence for Dark Matter - such as Darth Vador or something like that. I guess that you are telling me what I already know - not too darned much!!!
 

Offline Geezer

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The amount of dark matter required to "fix things up" is truly enormous. That suggests to me that our understanding of gravity and the nature of space needs a bit of a tuneup. (I expect I'll get some heat for even suggesting that!)

Our understanding of gravity is based on our observations on Earth and within our "near space". However, most of space is nothing like our near space. Our near space is, relatively speaking, chockablock with matter. Most of space contains next to no matter.

I think it is well accepted that gravity is caused by an interaction between matter and space, so, is it unreasonable to suggest that space behaves differently depending on the amount of matter it contains? If that is the case, we should not assume the laws of gravity that we observe in our near space are constant throughout the universe.

We already accept that distance between matter does create some profound, nonlinear, effects. We are still searching for a unified theory. Why would we assume that the gravitational effects that we can observe are linear throughout all of space?
 

Offline Mr. Scientist

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The amount of dark matter required to "fix things up" is truly enormous. That suggests to me that our understanding of gravity and the nature of space needs a bit of a tuneup. (I expect I'll get some heat for even suggesting that!)

Our understanding of gravity is based on our observations on Earth and within our "near space". However, most of space is nothing like our near space. Our near space is, relatively speaking, chockablock with matter. Most of space contains next to no matter.

I think it is well accepted that gravity is caused by an interaction between matter and space, so, is it unreasonable to suggest that space behaves differently depending on the amount of matter it contains? If that is the case, we should not assume the laws of gravity that we observe in our near space are constant throughout the universe.

We already accept that distance between matter does create some profound, nonlinear, effects. We are still searching for a unified theory. Why would we assume that the gravitational effects that we can observe are linear throughout all of space?

Because recent cosmological evidence suggests that the universe [is mostly] flat.
 

Offline Geezer

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Mr. S, Could you be a little more specific in terms of your source of information, or perhaps you would like to volunteer your explanation for the gigantic anomaly?
« Last Edit: 27/09/2009 01:51:50 by Geezer »
 

Offline Mr. Scientist

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Universe is flat and 'will be expanding forever' - Science, News ...But cosmologists have now demonstrated that the universe is almost certainly flat, which means it is full of a mysterious.
www.independent.co.uk/news/.../universe-is-flat-and-will-be-expanding-forever-720116.html - Cached - Similar -
 

Offline Geezer

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Mr S,

Kindly withdraw you "cheek" comment forthwith.

Geezer.
 

Offline Mr. Scientist

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Nevertheless, we can make averages of the visible mass and convert that into energy.

Imagine averaging everything down; so our sun is known to be an average sun, 2x 10^30 Kg of the stuff. There are also 10^24 visible stars in the universe. These facts are good enough to make some rough estimate:

1x10^24 x 2x10^30 x 3x10^8 x 3x10^8 = 18x10^70 joules

So there might have been roughly 18x10^70 joules; but this only makes a fraction of what is expected in a universe full of dark energy - so if our matter really does only account for 4% of everything, then the factors are multiplied, and we have something like 4.5 x 10^72 joules of energy that was present during the big bang. That is probably quite close to what we have, give or take a few tens.
 

Offline Geezer

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Mr S,

I say again, kindly withdraw your "cheek" comment forthwith. You can delete your post if you wish.

Geezer
 

Offline Mr. Scientist

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Stop copying my arguement.
 

Offline Geezer

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Mr S,

I am not copying your arguments (please note the spelling). I am simply asking that that you withdraw your pejorative "cheeky" comment because I dared to ask you to support your "authoritative" statement. If you do not wish to have your statements questioned, you might consider posting at a different site.
 

Offline JimBob

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Comment of someone asking a question:

If asking for the background references or an explanation is cheeky, I am going to do it again.

WHY
the assertion space is flat. A newspaper does not sate my scientific curiosity.

The assertion that space is flat is as sound scientifically as dark matter is, is it not? Both are explanations for a lack of understanding.


« Last Edit: 27/09/2009 03:20:13 by JimBob »
 

Offline Mr. Scientist

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Comment of someone asking a question:

If asking for the background references or an explanation is cheeky, I am going to do it again.

WHY
the assertion space is flay. A newspaper does not sate my scientific curiosity.

The assertion that space is flat is as sound scientifically as dark matter is, is it not? Both are explanations for a lack of understanding.



What does ''The assertion that space is flat is as sound scientifically as dark matter is, is it not?'' mean?


« Last Edit: 27/09/2009 03:21:20 by JimBob »
 

Offline JimBob

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Comment of someone asking a question:

If asking for the background references or an explanation is cheeky, I am going to do it again.

WHY
the assertion space is flay. A newspaper does not sate my scientific curiosity.

The assertion that space is flat is as sound scientifically as dark matter is, is it not? Both are explanations for a lack of understanding.



What does ''The assertion that space is flat is as sound scientifically as dark matter is, is it not?'' mean?





Both are explanations for a lack of understanding.

 

Offline Geezer

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Mr S

It appears you are unwilling to withdraw your "cheeky" observation.

I can only assume that you will be quite tolerant of similar pejorative observations directed in your direction. I will compile a long list, then I will get back to you.

Geezer
« Last Edit: 27/09/2009 03:39:31 by Geezer »
 

Offline Mr. Scientist

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There. Gone. Vanished. History. Sianara.
 

Offline Mr. Scientist

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Comment of someone asking a question:

If asking for the background references or an explanation is cheeky, I am going to do it again.

WHY
the assertion space is flay. A newspaper does not sate my scientific curiosity.

The assertion that space is flat is as sound scientifically as dark matter is, is it not? Both are explanations for a lack of understanding.



What does ''The assertion that space is flat is as sound scientifically as dark matter is, is it not?'' mean?





Both are explanations for a lack of understanding.



I was a bit lost, but i think i understand what you mean now.
 

Offline demografx

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It's "Sayonara", not Sianara.
 

Offline Geezer

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There. Gone. Vanished. History. Sianara.
Jolly good!

Isn't it so much nicer when we can have an intelligent debate without having to insult each other?

Clearly, there is a rather large disparity between our obseravtions of spatial bodies and our understanding of how those bodies should behave. Is this not so?
 

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