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Bill #53761 02/13/15 03:15 AM
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LOL you got me Bill I don't know your version of science at all and my byline admits everything doesn't it, I put it on every post. Perhaps you would like me to add some more to it smile

Seriously I think you mistake me for someone who cares what you think and that is a bit like worrying what Marosz thinks. Perhaps go for the appeal to the audience that is what those who need a crutch usually do next. I am sure there is a huge audience out there hanging off your every thought, Marosz is sure of it.

You really don't read anything I write and distort and lie what is actually said anyhow, so seriously why would I waste my time explaining anything to you. I am just really enjoying you explaining the real science my little "Bill in the box" and I am learning so much smile

Now back on topic you need to explain to Bill S how the energy pressure thing works as it really is the basis of his pondering about deforming space energy.

So Energy has negative pressure, equal in magnitude to its (positive) energy density explain the "real science" to us please

As you say I know nothing of this stuff so I really can't help or offer any hints smile

Last edited by Orac; 02/13/15 04:31 AM.

I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.
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Orac #53763 02/13/15 02:18 PM
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I'm willing to learn, if you will explain it in simple terms that I can understand.

Bill Gill


C is not the speed of light in a vacuum.
C is the universal speed limit.
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Originally Posted By: Orac
Now back on topic you need to explain to Bill S how the energy pressure thing works as it really is the basis of his pondering about deforming space energy.


I assume you are making a distinction between "energy pressure" and "pressure energy". If not, there is a vast amount of research to do; if so, can you point in an appropriate direction?


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Originally Posted By: Bill S.
I assume you are making a distinction between "energy pressure" and "pressure energy". If not, there is a vast amount of research to do; if so, can you point in an appropriate direction?

Nice to see someone thinking on this forum so lets first do the standard science.

So the standard GR version basically has at the bottom of it the concept of dark energy (this is the hole that Bill and Rede fell down), you can't believe in GR but not in dark energy they are joined at the hip smile

There are two ways that it is conceptually taught as either a cosmological constant or as quintessence depending on the scientist you ask and what they believe/promote smile

The cosmological constant version goes that there is a cost to energize a portion of space. Why the cost exists involves a bit of hand waving and saying that is just the way it is. The key criteria it sets out are

1.) The vacuum energy density is constant because there is nothing for it to depend on. This fits back to the original premise of uniformity of all space.

2.) Using classical thermodynamics and assuming the constant exists and you consider the volume of space is finite. A change in volume (dV) requires work done equal to a change of energy E = -P*dV, where P is the pressure, E being energy. However as your space volume has increased and you assumed a cosmological constant for space then the total energy must have increased. So the conclusion is that P must in fact be negative to give you a positive energy value for (E) ... We don't allow negative energy in classic physics !!!!!

Now there are a number of problems in all that, some you will immediately see others are not so obvious. One important not so obvious problems is the cosmic constant is incompatible with the standard model at low matter denisities, how problematic this is depends on your faith in the standard model.

If the cosmological constant is your thing then the favoured model is called Lambda-CDM.

Your second choice quintessence conjectures a fifth unknown scalar force which is varying slightly over time. Paul J. Steinhard's cornerstone work on the idea is technical but should be somewhat understandable by even a layman

http://physics.princeton.edu/~steinh/steinhardt.pdf

Scalar fields are predicted by the standard model and string theory but there are problems with renormalization of a slow changing scalar field. Which set of problems is worse well that is in the eye of the beholder.

If you get excited by quintessence you may care to look at the most favoured model at the moment called slow rolling inflation.


So how do you distinguish between the two ... well in short detailed and prolonged measurement of the fundemental forces smile

Last edited by Orac; 02/16/15 01:19 PM.

I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.
Orac #53767 02/16/15 02:24 PM
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Originally Posted By: Orac
So the standard GR version basically has at the bottom of it the concept of dark energy (this is the hole that Bill and Rede fell down), you can't believe in GR but not in dark energy they are joined at the hip


We weren't discussing the implementation of GR. We were discussing the analogy of a bowling ball on an elastic sheet. We never got any place close to dark energy, just the one simple analogy and how it worked. The only hole I fell down was the one created by the ball. And of course your farfetched claims about what I am saying.

Originally Posted By: Orac
Why the cost exists involves a bit of hand waving and saying that is just the way it is.

That's what all science is. All science, including QM basically is a description of "how it is". It doesn't tell us anything about why. Planck in particular wasn't trying to invent a whole new branch of physics. He was just making up something that made it work. I don't think he even really believed in it as anything other than a gimmick.

Bill Gill


C is not the speed of light in a vacuum.
C is the universal speed limit.
Bill #53768 02/17/15 01:28 AM
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Originally Posted By: Bill
We weren't discussing the implementation of GR. We were discussing the analogy of a bowling ball on an elastic sheet.

So what is it an analogy of .... this should be interesting smile

You may also care to note Bill S asked specifically how it worked under GR but obviously you don't bother reading what he writes either eek

The fact you didn't realize you had to introduce dark energy speaks volumes of your ability to answer the question asked. I am waiting for the "Bill in the box" corrections to my undoubtedly wrong views on Dark Energy smile

Originally Posted By: Bill
And of course your farfetched claims about what I am saying.

Ridiculous claims about what someone is saying, do you find it irritating ... you never do it to me do you smile

Originally Posted By: Bill
Originally Posted By: Orac
Why the cost exists involves a bit of hand waving and saying that is just the way it is.

That's what all science is. All science, including QM basically is a description of "how it is". It doesn't tell us anything about why.

That may be how "Bill in the box" science works. I guess I should be fair and ask do you believe this is a standard science consensus view?

Perhaps a hint of a warning from janitors who definitely don't practice "Bill in the box" science and it is usually expressed in a very precise phrase ..... Correlation does not imply causation smile

Bill S with his latin would recognize it as "cum hoc ergo propter hoc".

Last edited by Orac; 02/17/15 02:18 AM.

I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.
Orac #53769 02/17/15 02:58 AM
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I assume that you are saying that QM does indeed tell us why things are the way they are. I believe that QM is a set of equations that can be used to determine what will happen under certain circumstances. So given that you can tell me why, for example, entanglement happens. I know that the equations tell us that it will happen, but I don't know where in the equations we can find WHY. As far as I know modern science is descriptive. It doesn't go into why things happen, just how they happen.

Bill Gill


C is not the speed of light in a vacuum.
C is the universal speed limit.
Bill #53770 02/17/15 12:58 PM
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Ummmm if you bothered to read anything I ever said that is pretty much what I dislike about QM in it's current form (according to the science media) if we are forced to throw out string theory.

So yes to what you said and I pretty much complain that in it's current form QM is going down the GR/dark energy path. You may call that a janitorial criticism of both and the process smile

I don't feel compelled to believe everything that brain dead science media likes to propel as some sort of agreed take on things and which are bordering on crazy anti-science garbage. You can call it my janitorial license to do so and I can tell you I am not alone in my criticism.

You still never told me what the rubber sheet and ball was an analogy of ... perhaps worst ever Newtonian gravity model laugh

Anyhow lets see if Bill S is any closer to his answer.

Last edited by Orac; 02/17/15 01:49 PM.

I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.
Orac #53771 02/17/15 02:31 PM
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Well, now you have me completely bumfoozled. First you are saying that our bowling ball on a rubber sheet analogy for GR is incomplete because we don't include QM, now you say that QM is bad for some strange reason.

String Theory is probably going away some day just because nobody can make it give us any kind of a good match to what we see around us.

The bowling ball on a rubber sheet is the widely used analogy for GR as I said in the first paragraph above. That was part of Bill S' question at the start of the thread. So I don't see why you think I need to explain it to you again. It is after all what we started off talking about.

You still haven't answered my question about what dark energy has to do with the bowling ball. As far as I know dark energy wouldn't apply to the static case of the bowling ball. Dark energy would apply to dynamic systems, such as the universe. The bowling ball analogy is just a way for people to visualize the warping of space by a mass.

Bill Gill


C is not the speed of light in a vacuum.
C is the universal speed limit.
Bill #53775 02/18/15 04:34 AM
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Originally Posted By: Bill
Well, now you have me completely bumfoozled. First you are saying that our bowling ball on a rubber sheet analogy for GR is incomplete because we don't include QM, now you say that QM is bad for some strange reason.

Perhaps go back and read .. can you read Bill?

I never mentioned QM at all, in fact my only mention of it all was to tell, Bill S to ignore it smile

You really need to actually start reading what people say because I am starting to think you have signs of an age problem.

Originally Posted By: Bill
You still haven't answered my question about what dark energy has to do with the bowling ball.

And there in lies your problem ... you don't get it smile

Originally Posted By: Bill
As far as I know dark energy wouldn't apply to the static case of the bowling ball. Dark energy would apply to dynamic systems, such as the universe.

Really so dark energy only applies to a dynamic universe ... wow that is an amazing claim smile

Perhaps think about the positive pressure example Bill and an inflated car tyre and the car weight sitting on it .... or perhaps even a bowling ball laugh

Shall I give you a historic hint:http://en.wikipedia.org/wiki/Static_universe
Einstein's static universe is closed (i.e. has hyperspherical topology and positive spatial curvature), and contains uniform dust and a positive cosmological constant

Originally Posted By: Bill
The bowling ball analogy is just a way for people to visualize the warping of space by a mass.

That is because the rubber sheet provides elasticity, perhaps think about what provides the elasticity in space Bill. We don't really call it elasticity but it has the same deform behaviour (using Bill S words and idea) and something has to snap the deformation back which Bill S was wondering about and even if a partial deformation could remain. We give the thing doing this a name under GR, want to guess what it is? smile

Lets see if the penny drops yet. The incompleteness had nothing to do with QM ... do I need to repeat that 20 times so it sticks ... wait let me make it red.

However you left something else out, a name we shall not speak apparently smile

So your question is under GR the mere act of putting energy and/or matter into a bit of space (static or moving) does something ... what is it?

Last edited by Orac; 02/18/15 05:27 AM.

I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.
Orac #53777 02/18/15 02:26 PM
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OK, I give up. You really don't see that Bill S. had a simple question about the analogy of a bowling ball on a rubber sheet. And that the problem was that it was a simple analogy. I answered his questions about it based on the fact that it is an analogy and analogies are always imperfect. But the bowling ball analogy is just that and it is an extremely simplified analogy. It does not embody the whole of GR. GR is much more complex than the analogy. The bowling ball is a simple analogy that allows somebody to envision how space is deformed by a mass. That is ALL it does. It doesn't get into any of the other aspects of GR. You, in your usual manner, have tried to invest this simple analogy with a huge load of mystery that only you can understand.

Bill Gill


C is not the speed of light in a vacuum.
C is the universal speed limit.
Bill #53778 02/18/15 02:47 PM
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Bill S's question was asking the question of deformation of spacetime and while your analogy setup may provide basic child similarities it can't and doesn't answer the questions you need to deal with the issue properly and that means talking about dark energy and Stress–energy-tensors.

GR defines that putting energy and/or matter in any form into space creates gravity and is opposed by a repulsive dark energy force ... that is what GR says and how it works.

So your static bowling ball moving or not is opposed by dark energy just by the fact it exists as a clump of matter. You never got that originally and you still didn't get that in your answer above in fact you insist the opposite smile

In some ways gravity creates dark energy but I have edited and steered away from that terminology because it can lead to some very wrong conclusions and so I have used the term opposed being more in line with classical physics.

Bonus point question: A photon contains energy and exists in spacetime does it create gravity under GR, even though it is mass less smile

Last edited by Orac; 02/18/15 04:06 PM.

I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.
Orac #53779 02/18/15 06:50 PM
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Quote:
A photon contains energy and exists in spacetime does it create gravity under GR, even though it is mass less


My first thought was "yes", but then I thought "Although energy can, seemingly, create gravity; isn't it more to do with the stress-energy tensor, than just energy?"

Tensors are a bit mathematical for me, but I suspect the answer might be "no", because there are lots of components to the S-E T and I don't think they are all appropriate to a photon.


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Another thought that has just struck me is, would we need a quantum theory of gravity to answer that question?


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We have a bonus question winner ... and yes you got all the various components and pass with an A+.

I did limit the question specifically to GR for a reason smile

So the answer is sort of conditionally yes under GR although as you said you can sort of argue condition exemptions etc. One of the problems is under GR there are many possible distinct definitions of the gravitational stress–energy–momentum pseudotensor because it is a very mathematical process which you also got. So the GR answer you derive may actually hinge on what definition you selected and it's funny watching two scientists go at it with different definitions smile

You got the final part that the actual true answer probably needs a full theory of gravity, so at the moment all we can say is probably yes without the full theory or an experimental result.

So you got every component that the question poses and did better than some scientists I have seen tackle the question. It is a really challenging question that usually sets of furious debate and is really fun to ask a particular group of physicists smile

Now I should say my GR is not up to date and it really isn't my thing and this may be a really interesting question to put to Ethan Siegel to get a really modern view on this.

Last edited by Orac; 02/19/15 02:10 AM.

I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.
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