Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Karen W. on 28/10/2008 06:14:48
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I understand that there has been electromagnetic Radiation that has been covering all matter sense the big bang.... How does this in effect create the cooling of the universe?
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I'm guessing you're asking about cooling as it relates to the cosmic microwave background (CMB) The idea is that the CMB is a bunch of photons that were released shortly after the Big Bang. At that point, the universe was really hot (~3,000 K), and radiated like a black body. This means it sent out a bunch of photons at relatively high energies (details here: http://en.wikipedia.org/wiki/Black_body). As the universe expanded, these photons got red shifted, meaning their frequency decreased (their wavelength increased). Since the energy of a photon is proportional to its frequency, f (E=hf), the more red shifted a photon gets, the less energy it has. And finally, since temperature is in a sense a measure of energy, we can interpret this red shifting as a decrease in temperature. (If you want to be more specific, I think you can match the current background radiation to a black body of lower temperature than 3000 K.)
If you're asking about cooling as the average temperature of matter in the universe, then as the universe expands there is less hot matter (such as stars) and more cold dark space/matter between it, so when you average things out, you get a lower temperature.
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Sorry It took me so long to get back here..
Yes, I was referring to the CMB.
So when the, black body is hot..the size of the photons being red shifted causes there to be less energy and thus causes a cooling...of that body? So different sizes of photons emit different wave lengths of light right?
So before the big bang.. was there a hot black body or would that only pertain to the remnants after the big bang...So could a star for example be a hot black body.. and thus be cooled by more light rays in the same way... ? I think I am confusede and doing a poor job trying to understand...
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Karen - photons do not change size. It is their wavelength that changes.
Photons do not emit light. Photons carry the electromagnetic (EM) force and what we call light is a small part of the EM spectrum. At different wavelengths photons are detectable as radio waves, microwaves, infra-red, light, ultra-violet, X-rays & gamma rays.
As for what existed before the Big Bang, we simply do not know. The black body radiation we call the Cosmic Microwave Background Radiation (CMBR) is a relic of Big Bang itself.
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OK.. I thought I had it really confused.. I know we don't know what existed before the big bang... so that part is straight I was wanting to know if a star could be considered a "BLACK BODY?"
As for the rest, I read and read and still had it all screwed up in my head...
Thank you for clarifying because the way I was seeing the photons was not making any sense to me in conjunction with what I was reading.. so I will go back and reread and try to make better sense of what was said.. so I can understand how that cooling takes place!
Thanks Doc...
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Karen W. - the expansion of the universe doesn't seem to occur where there is matter - only where there is not matter. However, the CMBR only exists in those regions where there is no matter (because once the CMBR meets matter it is either absorbed or reflected) so as the photons traverse the regions between matter, which are being stretched due to the expansion of the universe, the photons get stretched too.
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LeeE the expansion of the universe occurs eveywhere but iside any material body its effects are far to small to be detected or cause any change to the body This even applies to very extended bodies like solar systems and galaxies
Karen W stars do like most other hot objects radiate like "black bodies" on the whol. There are some minor deviations caused by materials in the stars atmosphere (the chromosphere) which cause the spectral lines in what is essentially a black body radiation pattern dependant on the temperature of the star. These spectra lines are vital for understanding the composition and evolution of stars.
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Ian - in the program about dark energy I was watching on Discvoery Science the other day they said that the expansion is not happening inside galaxies as gravity holds it in check. The dark energy is there, but gravity overwhelms it.
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That is precisely what I said. Maybe I ommited to say that the effcts of the electromagnetic and gravitational interactions totally overwhelm the effects of the expansion of space whish however is presumed to happen. However it has been suggested that the expansion of space may not be totally uniform over the entire universe and may occur more in areas where there is very little ordinary matter or greater concentrations of dark matter but this would be very difficult to detect.
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However it has been suggested that the expansion of space may not be totally uniform over the entire universe and may occur more in areas where there is very little ordinary matter or greater concentrations of dark matter but this would be very difficult to detect.
If gravity overwhelms dark energy then what you said is true. The more matter there is, the more gravity there is so the greater extent to which dark energy is held in check.
I'm not sure whether your comment about dark matter is just a mistake or whether you meant it as it reads. Greater concentrations of dark matter would also help keep dark energy in check as dark matter is subject to gravity.
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I do not believe that you are thinking correctly here. You appear to be thinking that the dominant effect renders minor effects non existant. If I have three lights in a room one is one watt one ten watts and one one hundred watts. It will not make much difference if I switch either the one watt or ten watt lights on or of but when they are all on there are still three lights in the room it is the same with the dark energy expansion it may not make any difference but it is still there.
As for dark matter concentrations increasing the overall expansion of the universe. Just consider for a moment if some of the dark matter was in some way "particles of space" with a small mass and lots of energy but only interacting gravitationally. let these particles very rarely interact with one another to create another particle of space by converting some of its energy into another bit of space. This could create a situation where the universe as a whole expanded but it would expand faster where these particles were most concentrated.
I am not suggesting that this is so (or very likely to be) but I am trying to illustrate how the expansion of the universe may be slightly uneven.
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I do not believe that you are thinking correctly here. You appear to be thinking that the dominant effect renders minor effects non existant. If I have three lights in a room one is one watt one ten watts and one one hundred watts. It will not make much difference if I switch either the one watt or ten watt lights on or of but when they are all on there are still three lights in the room it is the same with the dark energy expansion it may not make any difference but it is still there.
Ian - I believe I am thinking correctly. I did not say that dark energy does not exist where there is matter, just that the effect of gravity overwhelms it and holds it in check.
As for dark matter concentrations increasing the overall expansion of the universe. Just consider for a moment if some of the dark matter was in some way "particles of space" with a small mass and lots of energy but only interacting gravitationally. let these particles very rarely interact with one another to create another particle of space by converting some of its energy into another bit of space. This could create a situation where the universe as a whole expanded but it would expand faster where these particles were most concentrated.
It's very interesting that you should say that. I have been thinking about GR, gravitons & gravitational fields. My musings were in response to a thread about gravitons and black holes. GR says "Matter warps spacetime and spacetime tells matter how to move". It does not, though, state how matter warps spacetime. I started pondering whether they may be something very fundamental about spacetime that gravitons could interact with and thus cause the warping. Maybe your dark matter spacetime particles could be what gravitons interact with.
Or could it be to do with dark energy? Let's take the viewpoint that dark energy does indeed exist where there is gravity but that gravity holds it in check (the accepted viewpoint). Spacetime is trying to expand, but cannot. So what happens? It bunches up. The greater the concentration of matter, the greater the bunching. It becomes more and more compressed the nearer to mass it is. Could that be the warping of GR spacetime?
Hang on - have I just suggested that gravity doesn't actually exist? [???]
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GR says "Matter warps spacetime and spacetime tells matter how to move". It does not, though, state how matter warps spacetime.
Yup - as gravity acts over great (potentially infinite) distances, this is key to it all. There is a clear implication that something (let's say a particle of some sort) originating from the mass ends up distant to the mass.
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GR says "Matter warps spacetime and spacetime tells matter how to move". It does not, though, state how matter warps spacetime.
Yup - as gravity acts over great (potentially infinite) distances, this is key to it all. There is a clear implication that something (let's say a particle of some sort) originating from the mass ends up distant to the mass.
LeeE - that doesn't necessarily follow. If you pull 1 end of a piece of elastic, it will have an effect on the other end, but no particle has been sent there. If, on the quantum level, space is cohesive, then all that dark energy building up in 1 place could have a knock-on effect.
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Karen
You're in space outside your space-lab being still, holding your trusty lighted light-bulb at your side, brightly shining.
Then you see that evil space-monster coming crablike towards you, you throw your glowing ligh-bulb at him as fast as you humanely can, while you grab hold of that trusty space-labs door, ready to hide.
What will that monster see in form of the lights wavelength, when the light-bulb travels toward him.
As the bulb flies towards him the light-waves 'shooting out' from it will be seen as 'compressed' from the monsters side.
But from your side, as the light-bulb now is speeding away from you, (you did try to throw it at the monster after all) Those light-waves traveling back at you will seem 'spread out' as they have a constantly larger distance to travel as the light-bulb moves away from you.
The reason for this is that light, no matter from where you measure it will have the same speed in space 'c'.
But somehow it will have to take care of the added energy it gets when it meets you though, as well as the lost energy we see it loosing when it's moving away from you.
If you think of a police-car passing you, the same effect will be noticed as the sound gets compressed when the car is speeding towards you, and then change pitch again as it travels away from you.
(Thinking of cars crashing at different speeds, I believe we all agree that different speed creates different energy-impacts:)
The way it takes care of that energy is by stretching out the waves when moving away(You<---->light-bulb), that's called redshifting as the colorspectrum gets redshifted when you see that light.
When moving towards you the waves from that object (light-bulb ---><--- monster) will become more energized as it gets compressed, and that's blueshift. Energetic light is a bluish white (the Sun)
We all know what cold is, don't we:)
It's when all movement stops inside a molecule
The stiller that molecule becomes the colder it will be.
But did you know that the same is true for a photon (no waves at all will be very coold...)
And that's how they stopped light, by cooling the waves/photons using lasers to quench those light waves.
If I got that right:)
So now you either have gotten a better grip on photons redlight/bluelight or you're even more confused::))
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Thanks lee for helping to explain..
thank you too Doc and Ian...I have to reread those posts.. are way over my head....I will break them down a bit and read again...
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Karen
You're in space outside your space-lab being still, holding your trusty lighted light-bulb at your side, brightly shining.
Then you see that evil space-monster coming crablike towards you, you throw your glowing ligh-bulb at him as fast as you humanely can, while you grab hold of that trusty space-labs door, ready to hide.
What will that monster see in form of the lights wavelength, when the light-bulb travels toward him.
As the bulb flies towards him the light-waves 'shooting out' from it will be seen as 'compressed' from the monsters side.
But from your side, as the light-bulb now is speeding away from you, (you did try to throw it at the monster after all) Those light-waves traveling back at you will seem 'spread out' as they have a constantly larger distance to travel as the light-bulb moves away from you.
The reason for this is that light, no matter from where you measure it will have the same speed in space 'c'.
But somehow it will have to take care of the added energy it gets when it meets you though, as well as the lost energy we see it loosing when it's moving away from you.
If you think of a police-car passing you, the same effect will be noticed as the sound gets compressed when the car is speeding towards you, and then change pitch again as it travels away from you.
(Thinking of cars crashing at different speeds, I believe we all agree that different speed creates different energy-impacts:)
The way it takes care of that energy is by stretching out the waves when moving away(You<---->light-bulb), that's called redshifting as the colorspectrum gets redshifted when you see that light.
When moving towards you the waves from that object (light-bulb ---><--- monster) will become more energized as it gets compressed, and that's blueshift. Energetic light is a bluish white (the Sun)
We all know what cold is, don't we:)
It's when all movement stops inside a molecule
The stiller that molecule becomes the colder it will be.
But did you know that the same is true for a photon (no waves at all will be very coold...)
And that's how they stopped light, by cooling the waves/photons using lasers to quench those light waves.
If I got that right:)
So now you either have gotten a better grip on photons redlight/bluelight or you're even more confused::))
Now you are speaking my language!!!
(hankyou for your analogies they do help a great deal for my brain... thank you very much..and welcome to the forum!
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GR says "Matter warps spacetime and spacetime tells matter how to move". It does not, though, state how matter warps spacetime.
Yup - as gravity acts over great (potentially infinite) distances, this is key to it all. There is a clear implication that something (let's say a particle of some sort) originating from the mass ends up distant to the mass.
LeeE - that doesn't necessarily follow. If you pull 1 end of a piece of elastic, it will have an effect on the other end, but no particle has been sent there. If, on the quantum level, space is cohesive, then all that dark energy building up in 1 place could have a knock-on effect.
But what would be the 'knock-on' mechanism? What is it that would be knocked upon, and what is the knock delivered with? In the elastic band there are the linked molecules of elastic acting upon each other - wouldn't you then need some sort of sub-graviton structure for this mechanism to work? If gravity propagates at finite speed, it really does suggest that something is moving (although going back to the elastic band idea, if you postulate that gravitons are more like a line than a particle you could have one end of it attached to it's originating mass, and the other free end moves away from it. Only problem then is achieving the inverse-square characteristics, so although the fixed end could start as a line, at the free end it'd have to look something more like a plane. Or perhaps the other way around)
Gravity must be one of the best puzzles ever - the only trouble is that we can't glance at the bottom of the page to find the solution [:)]
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Spacetime is itself could be the medium of propogation through its interaction with dark energy & gravitons.
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Spacetime is itself could be the medium of propogation through its interaction with cark energy & gravitons.
Doesn't that mean that space-time has to be made out of something?
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Exactly. You mentioned dark energy particles & I said I wondered if that could be it.
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It wouldn't have been me that mentioned dark energy or dark energy particles - I don't hold with such shady schemes. I think it might have been SoulSurfer, who said:
Just consider for a moment if some of the dark matter was in some way "particles of space"[...]
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LeeE - my mistake, it was Ian.
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Where did the idea of cooling universe come from? Our universe is a closed system so neither heat escapes from our universe to somewhere nor heat comes into our universe from somewhere. So what ever heat the universe has at its beginning, it still has the same amount of heat : Remember energy can neither be created not destroyed but it can be convertible. The only difference is that since the universe is expanding, the total heat is distributed in the whole space due to which the amount of heat content at a particular place is decreasing.
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kancha - the overall amount of heat in the universe will remain constant unless it is converted to some other type of energy, but as the universe is expanding that energy is getting more & more dilute (although some may quibble about my use of the word "dilute") thus causing the average temperature to fall.
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Yup - same quantity of energy, just spread thinner.
Mmm... there's a thought; Is entropy chasing the expansion of the universe? If the universe wasn't expanding, the energy within it would would nearly completely equalise relatively quickly, leaving no, or extremely low, energy gradients where work could be done. From an anthropic point of view, expansion would then seem to be necessary for a universe where work can be done on a long-term basis, as it results in an energy gradient for as long as the expansion continues.
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Well, yes I suppose so. It depends when you want to 'stop' the universe. Obviously if you stop it at the singularity then minimum entropy reigns and nothing happens.
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I understand that there has been electromagnetic Radiation that has been covering all matter sense the big bang.... How does this in effect create the cooling of the universe?
Because, as you might imagine, the continuous expansion of spacetime means that the real matter and energy contained within it is being diluted more and more; this added area, an infinite amount of expansion, is cooling the universe down.
If you traced the evolution back to some point, only a few chronons after big bang, we find the energy all stacked up very close proximity to each other, in a very hot gas of particles.
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Well, yes I suppose so. It depends when you want to 'stop' the universe. Obviously if you stop it at the singularity then minimum entropy reigns and nothing happens.
Yup, what I was thinking. It would have consequences for an expanding universe where the rate of expansion was decreasing, or where expansion ceased and it started to contract. In the first case, of decreasing expansion, entropy could overtake the rate of expansion, and in the second case, where a universe had reached the limit of expansion and started to contract, entropy would bring about the end of everything well before the big crunch.
A universe that increases it's rate of expansion seems to be the only really long-term solution.
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You also have the proposal where all types of energy and 'anti energy' in our universe together would become zero and null.
If that would be true expansion won't mean a thing, as well as spontaneous matter creations and virtual particles.
Seen that way our universe as easily could be just one like those...
Virtual particles, 'popping up' and then disappearing.
And the 'time' we have for defining our direction in spacetime.
Would then be much the same as for defined inside a VMO.
As all energy becomes null.