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Because there are other circumstances- like being inside a large but finite cold box where the CMBR would be exactly the same.
As we take out the imaginary walls from the infinite cubes in that infinite Universe, we would still get exactly the same CMBR.
You have only two options to get the blackbody radiation:1. Inside an "opaque and non-reflective object" at any finite size.2. In infinite universe size.
OK, do you now see that you have more than 2 ways to get BBR?
The walls of my cellar are whitewashed.
we all can agree that in an "opaque and non-reflective object" cube the radiation must be black body.
I have moved all the stuff out of it.And I have a single candle in there. The flame is burning at about 1200 CWhat is the colour temperature of the radiation in the room?
Imagine I go outside on a foggy moonless night.I have that candle with me.What does the radiation that i can see look like?What about if it's a foggy night and there are lots of candles around me- each one too far away to see properly but together lighting up the place.What does the ambient radiation look like?
And imagine that, since then the universe has expanded, stretching that radiation.
And imagine that, since then the universe has expanded, stretching that radiation.What; in that hypothetical universe, would you see in the night sky?
I told you it's 14 billion years old.I told you that it expanded nd so on.And, since it's my "model" universe those facts are true.What would you see in the night sky?
Plain wrong.The walls of my cellar are whitewashed.
"In order to make a blackbody spectrum, an object has to be opaque, non-reflective and isothermal."
"Thus a star, which is opaque, does not produce a blackbody spectrum because we can see both cooler outer layers and hotter deeper layers."
No walls means - No BBR.
So, if you insist to have a BBR in that imaginary finite Universe which exists in your imaginary model, then you MUST
QuoteQuote from: Dave Lev on Today at 05:29:34"In order to make a blackbody spectrum, an object has to be opaque, non-reflective and isothermal."NoThat is a sufficient, but not a necessary conditionDo you understand the difference?Do you realise that a tungsten lamp emits a very near blackbody spectrum?Do you think it's a box with a hole in it."All alsatians are dogs" is not the same as "all dogs are alsatians."
Quote from: Dave Lev on Today at 05:29:34"In order to make a blackbody spectrum, an object has to be opaque, non-reflective and isothermal."
http://astro.ucla.edu/~wright/CMB.html"In order to make a blackbody spectrum, an object has to be opaque, non-reflective and isothermal."
Quote from: Dave Lev on Today at 05:29:34No walls means - No BBR.That is not true.It does not matter how often you say it; it remains false.They only need to be "optically thick".
I can point out that the entire universe was, at that time opaque.Everywhere was a "wall" as far as light was concerned.
That's the point you keep missing.
"optically thick" can't be considered as a wall.
Then, you don't have to argue with me. You have to argue with them.
How could you reject the clear explanation which had been given by our scientists?
Then show the article that could support your unrealistic understanding.
Sorry, that "optically thick" isn't part of the requirement from a BBR as explained clearly by our scientists.
how an "optically thick" could be considered as a wall for a cellar.
an "optically thick"
What would you see in the night sky of that model universe?
QuoteQuote from: Dave Lev on Today at 18:04:35Then show the article that could support your unrealistic understanding.I don't need an article;
Quote from: Dave Lev on Today at 18:04:35Then show the article that could support your unrealistic understanding.
then it proves that your understanding is clearly unrealistic and there is no need to continue the discussion on this issue.
So, rather than posting nonsense, just answer the question.Quote from: Bored chemist on Today at 08:36:32What would you see in the night sky of that model universe?
I can point out that the entire universe was, at that time opaque.Everywhere was a "wall" as far as light was concerned.That's the point you keep missing.
QuoteQuote from: Dave Lev on Yesterday at 19:50:46Then it proves that your understanding is clearly unrealistic and there is no need to continue the discussion on this issue.NoIt shows that I recognize there is a real world out there.You don't need to look at a wiki article; you need to look at reality.But, since you insist.Like I said, the light from a tungsten lamp looks like BBRhttps://en.wikipedia.org/wiki/Color_temperature#/media/File:Spectral_Power_Distributions.png
Quote from: Dave Lev on Yesterday at 19:50:46Then it proves that your understanding is clearly unrealistic and there is no need to continue the discussion on this issue.
The universe is not, and never was "a star".
Why do you think that this lamp can support your unrealistic ideas about the Universe' BBR?
You actually claim that based on the BBT there were some sort of "walls" all around the early Universe.
So, how can you now compare the Universe to a lamp?
Sorry, you have totally failed to show how our current finite Universe without any walls around it could carry a BBR.
QuoteQuote from: Dave Lev on 04/10/2020 19:35:10You have only two options to get the blackbody radiation:1. Inside an "opaque and non-reflective object" at any finite size.2. In infinite universe size.In reality, most things emit something fairly close to BBR.Go and do some research.
Quote from: Dave Lev on 04/10/2020 19:35:10You have only two options to get the blackbody radiation:1. Inside an "opaque and non-reflective object" at any finite size.2. In infinite universe size.
Quote from: Bored chemist on Yesterday at 08:36:32I can point out that the entire universe was, at that time opaque.Everywhere was a "wall" as far as light was concerned.
Quote from: Bored chemist on Yesterday at 18:27:33So, rather than posting nonsense, just answer the question.Quote from: Bored chemist on Today at 08:36:32What would you see in the night sky of that model universe?
I'm a spectroscopist.
Now when we discuss on Black body radiation it is urgent to you to shift it again to night sky
Quote from: Bored chemist on 28/03/2020 10:44:30But I predict that Dave isn't even going to address the fact that he was wrong in the first few lines.I was right.
while based on your messages it is very clear that your knowledge in science is quite poor
Quote from: Bored chemist on Yesterday at 20:22:13Quote from: Bored chemist on Yesterday at 18:27:33So, rather than posting nonsense, just answer the question.Quote from: Bored chemist on Today at 08:36:32What would you see in the night sky of that model universe?
I am one of our scientists you idiot.
Quote from: Bored chemist on Yesterday at 13:49:31Quote from: Bored chemist on Yesterday at 20:22:13Quote from: Bored chemist on Yesterday at 18:27:33So, rather than posting nonsense, just answer the question.Quote from: Bored chemist on Today at 08:36:32What would you see in the night sky of that model universe?
SorryI have no intention to continue the discussion with you.Please stop posting any message in this thread.
If there was no space, than what was there?
Why do we claim that there are no walls around the expanding space?
it is very clear that there must be some sort of walls or barrier between R to R+1.
Therefore, how can we claim that there is no walls around our expanding universe while it is clear that at any given moment there must be a significant difference between the space inside that R to the space or no space outside R (or R+1).
matter, why do we assume that the temp of the matter or the CMB should be decreased?