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Post by Progenitor A on Mar 31, 2011 8:06:08 GMT 1
Dr Carroll Of Caltech told us on a recently posted video clip that dark energy is th emajor constituent of energy in the universe Well,if we accept, for the sake of argument, that Dr Carroll is right and that the all the energy of the universe is composed of just 4% ordinary matter, 25% dark matter and the rest dark energy, and that it is this dark energy that is causing acceleration of expansion of the universe, then there is something truly odd going on. Firstly he hypothesises that the reason space is expanding is that the dark energy pushes against space causing it to expand. Now the truly astonishing assertion behind this hypothesis is that the density of dark energy remains constant per cm 3 and it is this constant generation of 'new' energy (confounding the 1st law of thermodynamics - see another thread) that provides the necessary energy for expansion. For this assertion (quite apart from confounding the 1st law) goes quite contrary to many many of our physical laws, and if 'ordinary' energy followed this assertion, then life would not be possible Just take an example of what would happen to 'normal' energy if its density remains constant per unit volume Take the sun That has a radius of about 1.5 million km It radiates about 4 x 10 26 J/s If we consider the radiated energy to be the total (it is not, by a long, long way) then the energy density of the sun's sphere is about 10 8 J/km3 Now, as this energy radiates outward, if it were dark energy that energy density would remain constant, so that by the time the radiation sphere had expanded to just twice the sun's radius there would by about 35 times more energy contained in that sphere. And as the radiant sphere gets bigger and bigger the total sun energy gets massively bigger Hence no life on earth. Or, as another example, the BBC World Service broadcasts about 1 MW from its Ascension Island transmitters. Now if this radiant energy were dark energy it means that by the time those radio waves reached us here in the UK they would simply blast through our radios making them unusable! And here's another mischievous thought (which to my delight causes some consternation amongst those that maintain that the galaxies are not actually receding from one another, but the space between them is expanding). If this creation of new dark energy is causing space to accelerate in its expansion, then that acceleration is not going to stop, is it? So space will eventually be expanding faster than the speed of light wont it? And that will not break any laws, because it is only space that is expanding and that has no mass does it? If anyone APART FROM STA has any views on this I would be interested
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Post by principled on Mar 31, 2011 11:41:34 GMT 1
Nay If space is mass-less, then one would require no energy to expand it. However, in this expanding space are located galaxies which do have mass and if the space between them expands then they must have been moved. Now, how does one do that without consuming energy? P
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Post by Progenitor A on Mar 31, 2011 12:01:36 GMT 1
Nay If space is mass-less, then one would require no energy to expand it. Very, very good point. Was just thinking that whilst I walked the dogs but unfortunately I had already posted my Nobel Prize application. Hope no-one notices when I go to Norway! However, in this expanding space are located galaxies which do have mass and if the space between them expands then they must have been moved. Now, how does one do that without consuming energy? P There's the mystery! Others, un-named , tell me that the galaxies are not receding, it is the space between them that is expanding Confused? No more than me! The magistrate wasn't when I tried that on for my speeding offence - claiming that I was not moving away from the camera very fast it was the space between my car and the camera that was expanding quickly She told me to f*** off, fined me £200 and five points! Yorkshire ba****d! So what is all that dark energy doing pi**ing about if its got no work to do! Waste of space!
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Post by speakertoanimals on Mar 31, 2011 12:30:16 GMT 1
What you have to remember with the expanding universe is that what enters into relativity isn't just the energy-density of stuff (e.g., the density of matter, say), but also pressure. And dark energy is WEIRD stuff, in that it has to have negative pressure equal to its energy density. One such quantity that does have negative pressure is the cosmological constant -- and hence the most embarrassing failure in physics, because when we compute the contribution to the cosmological constant from the vacuum energy of the various matter fields, we get it wrong by 120 orders of magnitude.
WHY negative pressure? When something like a gas expands by an amount dV at pressure P, it does work of PdV. Hence its internal energy has to fall by the same amount. But the cosmological constant gives space a constant energy density, hence when space gets bigger, energy change is e dV. Hence to be balanced by pressure term, P must be negative.
The point about dark energy is that it causes the expansion to ACCELERATE, not just expand. As regards ordinary expansion, General relativity handles that. So, GR includes the effects of matter and energy density and PRESSURE on space. And a natural prediction of that theory is that a static universe is actually UNSTABLE (why Einstein added the cosmological constant to try and get a static solution since that was the idea at the time), and the most natural solutions are a universe that either contracts (which surprises no one, matter attracts matter, that is gravity, yeah, hence contraction seems natural!), OR (what seems unnatural), just expands.
So, that is what makes the universe expand, because a universe filled uniformly with matter and energy just DOES either expand or contract. The cosmological constant/dark energy stuff is the extra term, that doesn't look like ordinary matter or ordinary energy, that causes EITHER accelerating expansion, OR accelerating contraction, depending on which direction your universe was going in.
Mistake here in thinking the first law is that fundamental. As I've said before, the REASON energy is conserved is that the laws of physics are invariant to translation in time. Its the symmetries of the laws of physics that matter, NOT just the first law set in stone.
Hence when space and time itself come into it, the invariance wrt time comies in LOCALLY in general relativity (space locally flat), hence energy and momentum conservation still a good idea locally in a curved spacetime. But whe it comes to the larger scale, and spacetime itself as well, then the symmetries become more complicated, and simple energy conservation isn't that straighforward.
However, as I've shown above, simple energy ideas explain WHY stuff that has a constant energy density per unit volume HAS to have negative pressure -- ordinary stuff isn't like that!
If you were genuinely interested in the ACTUAL physics (rather than just people opinion of your mistaken view of the physics), then you'd be prepared to listen whoever said it.................Even you NM can sometimes be right.........................
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Post by speakertoanimals on Mar 31, 2011 13:20:20 GMT 1
Just a quick version of WHY pressure appears in the Einstein equations.
Okay, we are used to the idea that space and time can swap about depending on your point of view. I say that object is stationary (ie moving purely in the time direction), YOU say it is moving in space as well.
Just sitting there moving in time gives us energy density. But since it being solely 'moving in time' is just one particular point of view, in order to accord with special relativity, we also have to include a possible 'moving through space as well' component.
Which is why (if anyone remembers the gravitational aberration stuff and why does the earth feel pulled by gravity towards where the sun IS, rather than where it WAS eight minutes ago when the light we see left the sun) Einsteinian gravity depends not just on mass/energy density, but also on how that mass is moving. So we get velocity-dependant terms for the sun, which explain the point above. And when it comes to the Einstein equations, means we get the energy/mass density terms we would have expected, but also the pressure terms as well. Matter effects space in terms of its mass density, but also in terms of how it is moving (which ends up as pressure).
And the pressure term is why we can have constant energy density per unit volume and negative pressure for dark energy, and hence NOT muck up ideas about energy conservation. The first law still okay(ish), even if we know recognise the actual first law as just a local approimation, and a statement about the symmetries of the laws of physics. The other symmetries give us conservation of moemntum and angular momentum in simple flat space, but the symmetries, and what is conserved, get a (lot) more complicated when spacetime itself joins the game.
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Post by carnyx on Mar 31, 2011 13:56:03 GMT 1
NM,
Your OP got me thinking. Where does that energy come from, and where is it going?
AFAIK, EM radiation from the furthest observed objects has dropped in frequency by a factor of around ten. This also means that it has lost ten times its energy on the way here.
Where has that energy gone? And putting aside explanations involving 'inflation' and stretching time, etc., what kind of mechanism would be required for EM radiation to lose that amount of energy?
On a per-cycle basis it is a very very tiny effect, in the order of 1.0E-33 or so. So it must be a very subtle mechanism indeed. And how is this energy radiated? In the form of 'ghost' EM waves perhaps, at very different frequencies, like eddies? Or has it been very slowly converted into complex modes of vibration that somehow reflect off all matter and are not absorbed, and so are not detected?
And with all that radiation whizzing about in all directions including beyond our horizon, all apparently dropping in frequency and so shedding energy 'in flight' as it were, what has become of this missing energy?
(BTW, here is a joke; every year the astronomers detect further and further objects. So, one could say that the cosmologist's theoretical rate of 'inflation' of the Universe has had to grow at least as the cube of progress of astronomy. Why? Because the light from the furthest object has also reached as far the other way .. as has the light from opposite objects.
So at this rate of expansion of expansion, pretty soon we really will be at infinity. And Lo! the Universe will regain it's property of infinity. So where will the Cosmological idea of expansion fit? I reckon they don't have much time to invent a new cosmology, so they had better get a move on!)
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Post by Progenitor A on Mar 31, 2011 15:06:38 GMT 1
Carnyx Modern physics is so counter-intuitive that we simply have to accept the words of experts. But much of it see,s sheer illogical madness. AS you say, where does all this new energy come from. AND we are in a positive feedback loop that goes like this; (according to Carroll) 1. Dark energy causes space to expand at an accelerated rate 2. New energy is created to fill the extra space 3. this new energy (+ the old energy) cause further acceleration in the expansion causing even more space 4. The new space fills with new energy to cause more accelerated expansion of space
Some things we can learn from this 1. Dark energy hasn't been around very long or it would dwarf everything else OR 2. The initial amount of dark energy was so infinitesimally small that it is only just beginning to assert itself OR 3. The whole theory is bollocks
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Post by Progenitor A on Mar 31, 2011 15:16:36 GMT 1
Compare this Googled stuff..... What you have to remember with the expanding universe is that what enters into relativity isn't just the energy-density of stuff (e.g., the density of matter, say), but also pressure. And dark energy is WEIRD stuff, in that it has to have negative pressure equal to its energy density. One such quantity that does have negative pressure is the cosmological constant -- and hence the most embarrassing failure in physics, because when we compute the contribution to the cosmological constant from the vacuum energy of the various matter fields, we get it wrong by 120 orders of magnitude. WHY negative pressure? When something like a gas expands by an amount dV at pressure P, it does work of PdV. Hence its internal energy has to fall by the same amount. But the cosmological constant gives space a constant energy density, hence when space gets bigger, energy change is e dV. Hence to be balanced by pressure term, P must be negative. The point about dark energy is that it causes the expansion to ACCELERATE, not just expand. As regards ordinary expansion, General relativity handles that. So, GR includes the effects of matter and energy density and PRESSURE on space. And a natural prediction of that theory is that a static universe is actually UNSTABLE (why Einstein added the cosmological constant to try and get a static solution since that was the idea at the time), and the most natural solutions are a universe that either contracts (which surprises no one, matter attracts matter, that is gravity, yeah, hence contraction seems natural!), OR (what seems unnatural), just expands. So, that is what makes the universe expand, because a universe filled uniformly with matter and energy just DOES either expand or contract. The cosmological constant/dark energy stuff is the extra term, that doesn't look like ordinary matter or ordinary energy, that causes EITHER accelerating expansion, OR accelerating contraction, depending on which direction your universe was going in. Mistake here in thinking the first law is that fundamental. As I've said before, the REASON energy is conserved is that the laws of physics are invariant to translation in time. Its the symmetries of the laws of physics that matter, NOT just the first law set in stone. Hence when space and time itself come into it, the invariance wrt time comies in LOCALLY in general relativity (space locally flat), hence energy and momentum conservation still a good idea locally in a curved spacetime. But whe it comes to the larger scale, and spacetime itself as well, then the symmetries become more complicated, and simple energy conservation isn't that straighforward. However, as I've shown above, simple energy ideas explain WHY stuff that has a constant energy density per unit volume HAS to have negative pressure -- ordinary stuff isn't like that! With this......... Total crap! You CAN make something warmer by reducing its heat loss This Joseph Postma is talking utter bollocks! .......it is total and utter garbage. ........ utter nonsense!...... is utter nonsense.......................... .....and it is pretty evident that she should try googling a Ladybird Science book!
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Post by speakertoanimals on Mar 31, 2011 15:17:01 GMT 1
Well, that's daft, since the usual explanation is in terms of stretching SPACE (which is expansion NOT inflation, two different things!).
First off, you're assuming that conservation of energy still holds in expanding and curved spacetimes. As I said where energy conservation COMES FROM is symmetry of the laws of physics under translation in time, and since symmetries changed in curved and expanding space and time, conservation of energy isn't totally straightforward when spacetime comes into the picture.
One simple answer, is that the energy lost from the CMB goes into the 'increased gravitational potential energy' of the whole universe, since it is the expansion of space that causes the loss of energy, hence that is where it goes.
Another answer (more correct, but far les intuitive), is that the redshift is a fairly straightforward prediction of general relativity, general relativity works better than any other alternative as far as we have been able to test it, and the 1st law, ionce we understand WHERE it comes from, isn't as sacrosanct as some seem to think. From the point of view of GR, conservation of energy is something that may be useful locally, but when space starts to come into it, it is no longer necessarily the case -- or at least stuff ain't that simple anymore! There are still symmetries in GR, just not as simple as straightforward translation in space. And perhaps we should have expected this, given that simple flat spacetime as in special relativity is already weird enough, where time, and lengths, and energy, and momentum, and almost everything else (apart from speed of light), ALL depend on your point of view!
So, the proper answer to the whole area is just that our commonsense notions of time and length had to get altered when we discovered that special relativity was needed. Similarly, notions of energy and momentum and angular momentum conservation get a bit more complicated when dealing not just with matter locally, but when we are trying to deal with the entire universe, AND all the matter and energy in it. What applies locally within the universe isn't necessarily what applies when considering the whole shebang. AND we understand why once we understand WHERE energy conservation (and similar conservation laws) come from! That's the essential point (good ole Emmy Noether figured that one out, the link between symmetries and conservation), except that since that link is mathematical, it isn't going to make much sense if all you have is some semi-intuitive notion based on just 'energy can be passed around and converted between various types but never destroyed'.
Daft. IF the universe IS infinite, it always was, hence no infinity to be regained! If finite, it will ALWAYS be finite, just get very, VERY, VERY big -- but not infinite. Just because something is infinite doesn't mean it can't expand -- just means you're stuck with the incorrect view of expansion as like stuff flying away from an explosion..........................
I now fully expect that neither carnyx or NM will pay any attention to any of this (apart from cutting & pasting with a few added emoticons), but heck, at least I've pointed out the misunderstandings, and someone else might find it useful, even if they don't.
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Post by Progenitor A on Mar 31, 2011 15:20:56 GMT 1
Carnyx An interesting little thing on the video - which was made at the Amercian Science Foundation, was that they put in a caveat at the start of the lecture stating that the views expressed were not necessarily theirs!
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Post by speakertoanimals on Mar 31, 2011 15:27:51 GMT 1
Sounds like a standard legal disclaimer -- views expressed are those of the person making them, not us as an organisation, just as when they have interviews etc on a DVD, we have the legal disclaimer at the start that explains views expressed are those of the individuals making them, not the company distrbuting them.
Nice to see that NM has conformed to my expectations, and just tried the usual silly nonsense. I should note that HE never did make clear whether or not he thought the Postma stuff was actually right! I SAID it was bollcoks because it was so BAD that bollocks was the only really appropriate word.
Which (if they were still going), would probably give a pretty decent Ladybird book on cosmology, and wouldn't make the same mistaken assumptions that you are carnyx seem to be stuck in (or perhaps wallowing in would be more appropriate?).
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Post by speakertoanimals on Mar 31, 2011 15:48:49 GMT 1
Here's a little thought experiment. Most of us are now slightly used to the idea that the energy that a thing has depends on your point of view. So, if aan electron is moving wrt me, it has more energy than if it were stationary.
But same goes for a photon. What frequency (hence energy) someone stationary wrt the source says it has is DIFFERENT to what I decide is the frequency when I detect it, because it just so happens (ordinary Doppler effect), that the source was moving relative to me.
WHERE did that energy go, someone might naively ask? Nowhere, say I, just that WHAT the exact energy was depends on your point of view.
Keep that in mind. Now think about the photon emitted billions of years ago from a glob of matter far far away, and think about that same photon when I detect it in my telescope. O dear, say some, it is redshifted, where did the energy go? Except to ASK that question, we would have to have a point-of-view that included both me here and now, and that glob of matter far in the past, AND that included the fact the space in between us has been stretching and curving and all sorts of stuff in the interim........................
The point being, such a god-like point of view just isn't feasible, just as in the first case, we didn't ask where did the energy GO, we just naturally accepted that different viewpoints give DIFFERENT values of the energy. Same in this case -- any observer who was there when the photon was emitted would have one view of what the energy was, anyone else at a different place and later time, will have a different view. Hence as long as we can predict what the different opinions will be based on a proper description of how the two observers are related, then that is that! We can't ask where did the energy go, because that assumes there is some god-like position fron which we can view the whole thing, and that energy conservation holds for everything from that place -- and we can show that this isn't necessarily true in general relativity.
So, energy conservation can hold good locally (when that photon interacts with my CCD, I can track the energy and assign a meaningful energy to the photon based on its frequency using a diffraction grating etc), but that doesn't mean it has to hold globally, in the sense of your opinion as to the energy it had when it was emitted, and my opionion as to what energy it had when I detected it umpteen billion years later. Even 'umpteen billion years' is a matter of opinion as well ........................
Or, it's all relative.........................
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Post by carnyx on Mar 31, 2011 16:11:49 GMT 1
@sta.
There are a few faults in your comprehension; which unfortunately render your post both elliptical, and redundant.
For example;
Look at the fifth word, which applies to all that follows .
STA. I suggest you read others' posts ( particulary mine) out loud in a deep manly voice (rather like Richard Burton's in timbre actually) ... to avail yourself of additional senses that MIGHT help you to comprehend more fully WHAT is being communicated .. and so you might not go off at tangents so much. And I suggest you get your OH to read your posts out, so that you can check that your are addressing the proposition as it were. Indeed it might help you get into good habits IF YOU WERE TO INITIATE A THREAD YOURSELF.
But, back to NM's thread topic.
Yes, NM. We have the basic values of mass, length and time. But our Cosmologists have convinced themselves that all can be explained and accounted for, if only time is stretched, lengths are bent, mass is somehow dematerialised, and definitions are confuted straight after they have been uttered.
Of course this deliberate incitement to chaos is the very definition of evil, stemming from a kind of rage. It is, simply, the devil's work.
So, sadly it is not possible to have any kind of rational discourse about Astronomy or Physics, at least whlie Cosmologists are about, and so I have to agree with your third postulate.
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