Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thebrain13 on 29/11/2006 04:03:06
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I dont understand the link between Cosmic Microwave Background Radiaton, or CMB for short, with the big bang. It is said that we see roughly equivalent amounts of mircowave radiation from all directions of the sky. And this has been refered to many times as the smoking gun for the big bang theory. I dont understand why, If all matter and energy spewed from one moment and point in the universe, wouldnt you expect the CMB to be from one point? I would of imagined this is what we'd see from a steady state theory. How does this disprove steady state theories and how does this provide proof for the big bang.
I dont even know where to start with this one.
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The point (if you'll pardon the pun) is that if all matter started from a single point, then we too started from that point. As all matter expanded equally, that whole point grew into a giant balloon that is the universe we see around us, so it is as if we were still within that same point - that initial point in the universe is not outside of us, but we are still within it, but it has simply got very large.
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Imagine this :
You're a very, very small person and you are at this moment living inside a large bomb.
Don't worry about the details here regarding the initial point singularity etc... forget all that for the moment.
Just think about you being inside this bomb.
There's nothing else around, just the bomb and you inside it.
You're surrounded by the explosive. That's all you can see, feel and experience.
Then, by some means (don't worry about the detail), the bomb explodes.
Miraculously you don't die, let's say you're a super person.
Now the bomb explodes.
Just at the instant of the detonation, just at the very, very start of the explosion when things have only just started to move so you stop time to give you a little opportunity to look around at your surroundings.
You see that all the explosive you can see has got a bit hotter. Well a lot hotter actually.
But it's still pretty much all together.
Now let's wind the time on by another small amount.
We're looking at the explosion from the inside here and we're doing it in very slow motion.
The explosion is now say, 10 feet across. What can you see ?
Remember you're inside the explosion.
You're being moved by the explosion. You're being propelled by the force released in the explosion.
But you're still inside the explosion.
By this time the bomb has been completely vaporised. It's now a very, very rapidly expanding cloud of extremely hot gas.
You're in the midst of this. Not at the centre of it because you've moved with the force.
You're in amongst the exploding gas but you're OK because you're super.
Lets wind time on by a whole second.
Now you lookj around and what do you see ?
You see lots of expanding gas that is very very hot.
And it's a lot less dense than it was.
As the beginning you were packed in tight. Now you're just in this big cloud of super hot gas.
Lets move time on a bit further.
The exploding cloud of gas gets bigger and bigger and you are still moving with some of it. You're still inside the explosion.
Although it's not much of an explosion anymore.
Now lets say that the cloud of expanding gas keeps expanding and you are still inside it remember.
What can you see ?
You can see gas around you getting thinner and thinner, getting cooler and cooler.
It used to be extremely hot but now it's quite cool.
Lets wind things on a bit more until the gas has cooled down a lot. Lets say the gas is at room temperature.
The gas cloud is still expanding, still getting bigger all the time but it's now a huge amount bigger than it was and it's an awful lot cooler than it was.
Now if we wind the clock on for a long time so that most of the gas has cooled down almost as far as it can then have another look around and what can you see ?
You see cold gas all around you. It's still expanding but it's pretty damn cold by now.
Some bits of it might be very slightly hotter than other bits of gas but not by much. Some bits are slightly cooler.
You're still inside the cloud remember.
You can only see this cold gas.
The slightly hotter parts are a bit hotter because the explosive in the bomb was a tiny amount more densly packed there or perhaps it burned hotter in the beginning at that point.
So you get out your telescope that you remember you happen to have in your back pocket and you have a look around the cloud of gas that you're inside of still.
You attach the special thermometer to your telescope so you can measure the temperature of whatever you point it at and you take some readings from different parts of the cloud you're in.
You take readings from different parts of your sky.
You start to realise that there are bits of it that are slightly different in temperature. You start to understand that 99.999% of it is the same temperature.
You ask yourself how can something that's way over there be the same temperature as something way over the otherside of there ?
You try to think of an answer. The only thing that makes sense is that they must have, at some time been in contact with each other.
That would make the different parts of the sky the same temperature even though they're now separated by vast distances.
So how did they get to be touching ?
You try and find out.
You look around with your telescope and you start to understand that the gas cloud is expanding. Bits of it are still moving.
In fact the more you look you realise that all of it is in fact moving and all of it is moving away from everything else.
If it's all expanding then maybe if you wind time back you'll find that it was all in the same place at the same time.
Ahhh ha !
At some point all the gas you see around you must have been collected together in one place.
Then something happened, you don't know what, to start it all expanding.
What you have just discovered is The Big Bang.
And all of that from your observations of the cold gas expanding all around you.
Easy huh ?
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Another point to consider is why the CMB (cosmic background radiation) has the wavelength that it does, and why it's still around where we are. Indeed, should it not have zipped past where we reside billions of years ago?
Obviously it didn't, because we can still detect it here today. And the reason is that the Big Bang unleashed radiation of a very short wavelength. But as the Universe expanded incredibly quickly, and continues to do so, these waves have "stretched" and are now within the microwave regime.
You can think of it as akin to stretching an elastic band between your two index fingers, and then moving your hands apart. It's the same elastic band but it's now much longer that it was before. So it is with the CMB radiation spawned by the Big Bang.
The CMBR was discovered by two scientists, Arno Penzias and Robert Wilson, in 1963. Together they helped to settle a long-running dispute about the state of the universe, and to seal the deal for the Big Bang theory.
In the 1950s, the Steady State Theory had been put forward by Hermann Bondi, Thomas Gold and Fred Hoyle. They suggested that the universe was fixed in space and time and had always been that way - in "a steady state."
But Edwin Hubble had found, in 1929, that distant galaxies were "red-shifted", that is they are moving away from us, and each other, at remarkable speeds. His interpretation was that the space between galaxies is constantly expanding. Another physicist, George Gamow, built on this foundation to suggest that, historically, the galaxies must have been much closer together. If one continued to wind back the cosmic clock, some argued, the universe would have been infinitely dense at one point, corresponding to the moment of creation; the Big Bang.
Arno Penzias and Robert Wilson brought the debate to a close by accident. They were studying radio emissions from the Milky Way, but they found background radio noise that they couldn't explain. It came from all directions in which they looked, and, after repeated checks, it appeared to emanate from outside our Galaxy.
It was then that the penny dropped that these mysterious radio signals corresponded to cosmic background radiation that had survived from the very early days of the universe. It was the smoking gun left behind by the Big Bang.
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I heard the interference and noise you hear coming from a tv when ayour tv isnt tuned into a station is due to CMR
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I heard the interference and noise you hear coming from a tv when ayour tv isnt tuned into a station is due to CMR
You're partially right.
Most of the "snow" on the screen is local interference, microwave ovens, radar, radio stations, taxi radios etc... etc...
But absolutely some of it is actually from the CMB.
I remember seeing, years ago, a filter you could buy to filter out most of the local rubbish and show you more of the CMB. Obviously the TV was no good for receiving programmes when you had it fitted to the aerial though.
The picture was still rubbish mind. Just snow but a slightly different type of snow.
Ahh the heady days of my RF childhood.
[:D]
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I heard the interference and noise you hear coming from a tv when ayour tv isnt tuned into a station is due to CMR
The best of TV tuners have self genrated noise equivalent to 300K, possibly by using some switching technique (see Dicke's radiometer) you could detect CBMR with one or at least some hot source of radio noise like the Sun.
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I heard the interference and noise you hear coming from a tv when ayour tv isnt tuned into a station is due to CMR
I remember seeing, years ago, a filter you could buy to filter out most of the local rubbish and show you more of the CMB. Ahh the heady days of my RF childhood.
[:D]
This sounds like a scam to me!, I would like to see the original add
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Aye, it probably was but it gave me great thoughts of home astronomy using the TV out in the garden.
[:D]