What exactly is this and where did it come from?
In detail if possible please
its the reminants from the plasma soup stuff that formed after the big bang. If you read into it a bit (not sure if the above link goes into it) you see that initially the universe was energy dominated, with any matter formed (photons can turn into matter and vice versa through quantum theory) was immediately broken up by the high energy photons wizzing around. After a while, due to cosmic expansion and the inflation period these photons redshifted to a point where they no longer had enough energy to do this and so matter clumped together and formed stuff like hydrogen and more stable things so the photons did not interact with them anymore (known, from memory, as recombination, which occured about 300,000 years after time zero) and so the universe went from being opqaue to transparent. this meant these photons continued flying out into space and redshifting untill they became what we see today as the cmb, a very cool reminants of a once hot photon plasma
I vote for ST's link, it is pretty concise. I usually find it easier to quote eloquent statements than compose them.
well i tried :P
You did a commendable job, FD. I very much liked what you said and did not intend to diminish your contribution to this discussion. Your knowledge of science is apparent, but your humility speaks volumes about your character and regard for dissenting opinions. I look forward to your future posts.
This may be a stupid question but:
If we can see Cosmic Background radiation in all directions, would that not indicate that we were in the unlikely position of being in the exact center of the universe (the place where the big bang happened). If we were closer to one edge or the other, we would not be able to see all the way back in one of the directions, because it would be further than 13 billion years away.
Alternately, it could (and is thought to) indicate that every point is at the center and there is no edge.
Sorry to press, but I don't exactly follow your answer. If the leading edge of the background radiation (not the edge of the universe) is , let's say 13 billion light years away. That is a finite distance. If I can see that finite distance in any direction, then it stands to reason, in my mind, that, unless the background radiation is something else, you would have to not be able to see the leading edge of the background radiation in at least one direction unless you were in the unlikely spot as being at the center of where the big bang happened.
The trouble is with your mental picture, the U as material expanding out into empty surrounding space.
One way to get a different image is to google "wright balloon model" and watch it. It is a 2D toy model of a 3D expanding space so imagine that all existence is concentrated on that 2D surface.
You will see small white flat galaxies scattered on the surface, getting farther apart but always staying at the same approximate (lat and long.) location on the balloon surface.
You will see small colored wrigglers traveling across the surface---these are photons of light.
Imagine being a flat 2D creature living in one of the galaxies. The amount of light you get is the same, on average, from every direction. (All directions are in the balloon surface, there is no surrounding space "outside" or "off" the surface. There is no center of expansion that you, as a 2D creature in that U can point your 2D finger at.)
Imagine that it is the same with us, except we are 3D creatures in a 3D space. The space has no edge, no boundary. There is nothing "outside". There is no center of expansion that we can point our fingers at. There is simply expansion.
And so the ancient light comes to us with approximately the same intensity from all directions.
Notice that the photon "wrigglers" of light start out being shortwavelength and blue, and as the 2D sphere surface they live in gets larger they themselves get stretched out and get longerwavelength. The artist/animator has emphasized this by having them change color as they get longer, from blue to green to yellow to orange to red.
This is a "false color" way of calling the viewer's attention to the change. A real CMB photon would typically start out, say, reddish orange (a 3000 Kelvin glow) and gradually fade into an infrared color that our eyes can't see, and gradually get longerwave and longerwave until it was in the microwave-oven millimeter radar part of the spectrum, so no visible color. The animation symbolizes that by showing the photons having false-color red.
You can get a lot of insight if you watch that simple 2-minute movie carefully.
It is always avaliable if you just google "wright balloon model".
But then the CMB would be propagating away from our central location. How would we see the CMB arriving at earth uniformly from all directions if we happened to be sitting at the center from whence all this light came?
As Marcus says, have a look at the balloon model; it's an incredibly useful visualization.
The Cosmic Microwave Background Radiation (CMBR, initially) is colloquially referred to as the ambient temperature of space, or "the temperature of space in all directions." As the universe is expanding, that is, all objects appear to be moving away from each other, we would expect this to change at some point. Penzias and Wilson observed the CMBR in 1964, confirming the prediction of Ralph A. Alpher (and later Ralph A. Alpher and Robert C. Herman) in 1948. Credit for the theoretical prediction is often given to George Gamow. Gamow opposed the idea on theoretical grounds. He began publishing his own calculation using a different method in 1955. The well-known "alpha, beta, gamma" paper of 1948 was a prepublication drawn from Alpher's thesis the month before he defended it; this dealt specifically with nucleosynthesis. A new paper on this historical quagmire is about to appear in Physics in Perspective (2012, issue 3 or 4), by Victor S. Alpher, Ph.D., Ralph A. Alpher's son.
SpaceTiger, all I can say: WOW!
I'm not an expert where it comes to cosmology but I have my dreams to be. However, I must say, I've read a lot astronomy related things, but I have never had such a visual picture inside my head while reading the thread "what is Cmb" that you posted.
I mean, it was like I could see everything I read clearly inside my head.
Thanks a lot! I must say you inspire me - I wish to do such writings as you in the future!
Robin Anderson, thank you for your response. I was 10 years old when the observation of the CMBR was announced. Knowing RAA and RCH very well, I have been able to follow developments in the acceptance of the Big Bang theory closely. Conceptually, G. Gamow contributed the idea of "hot, dense" beginning of the observable universe in 1946. Ralph A. Alpher worked out the actual theoretical proposal of nucleosynthesis in his dissertation. The bulk of his dissertation, as promised, was published in the December, 1948 Physical Review. Meanwhile, he had published, with Herman as 2nd author, the first quantitative prediction of the "relict" CMBR that should be omnipresent today. Radioastronomers of the time told them repeatedly that it could not be measured with then-current technology. It may have been observed (even through spectral analysis), but was never interpreted in a cosmological context until publication of Penzias and Wilson's observation in 1965 (Astrophysical Journal; the observation was made in 1964). The literature attributing the prediction to G. Gamow (which continues) is incorrect. RAA was finally recognized for his seminal work in the citation to the 2005 National Medal of Science (actually awarded on 7/27/2007). I am pleased that I provided some clarity for you.
If you travelled a considerable distance (in any direction) and then looked around you would see a different view of the universe and you would also see a different view of the CMB. You appear to be in the centre of the CMB for the same reason it always looks as if your in the centre of the universe, its everywhere.
No one position is privileged. Wherever you are, the you see expansion as a Doppler shift.. 13 million years, if we agree on that tentatively, is as far back as we can see now. Measured from the earth, as Penzias and Wilson did, or space, as tbe COBE did, you get a blackbody Planck spectrum at 2.725 degrees K. COBE brought the measurement to a high degree of precision--one of the most precise measurements in cosmology and astrophysics. Extraneous sources of radiation have been effectively eliminated.
To Remmeler and QuantunHop: The expanding balloon metaphor was often used by RAA to explain this to lay audiences. From any position, one sees expansion. There is no center or "privileged" position from which to observe or measure.
Hi all, I understand (to the best of my ability) the origin / nature / age of the CMBR and I have seen the above timeline previously in many sources and threads. I understand that we can use redshift to estimate the age of the CMBR, but can someone explain what process (or mechanism) is used to estimate that this happened 300k years after the BigBang? (i.e. How / why do we not think that it took 30k or 3m - does nucleosynthesis require 300k years to create enough hydrogen, or is there another mechanism for estimating the age of the univerese as CMBR + 300k years?)
And another question regarding the CMBR. I heard no matter where you are located in the universe, you measure the same distance to this "wall" of radiation, in all directions. If this is true, can someone explain it? I can't understand how.
Robin, This is correct. Have you looked at any of the balloon / raisin analogies? The important thing is not to think of the BigBang as an explosion out from a point, instead think of it is as an inflation, everywhere, at the same time (like the surface of an inflating balloon or a loaf of bread rising in an oven). If you were standing on the surface of the balloon (or on any of the raisins in the loaf), it would appear as if you were at the center of the expansion / inflation, no matter which / where you were standing.
I hope that this helps, but if not, there are lots of threads in the forum that go into more detail ("phinds" is a regular poster and has a web page that is great).
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