Zero Total Energy

[Polednice]

I've recently been listening to some talks by Peter Atkins, a chemist and popular science writer, and I've heard him a couple of times talk about the beginning of the universe in terms of "nothing coming from nothing." This is because he says that current data in cosmology tentatively indicates that the universe might have a total energy of 0, and, therefore, the universe ought not be considered to be something coming from nothing, but nothing separating into its component, self-annihilating parts.

 

Is there a name for this theory in physics? Does it have many proponents? Can anyone elaborate on it for me?

[ACG52]

but nothing separating into its component, self-annihilating parts.

 

 

This bit sounds like a little poetic license, but the idea of a zero net energy universe originating in a quantum fluctuation was first proposed by a physicist named Edward Tryon in the late 1960s

[timo]

I don't know exactly all the contributions that are taken into account, but I was under the impression that the mainstream view is that the average energy density of the universe (and therefore the total energy) is distinctively non-zero. From the first random Google hit (http://map.gsfc.nasa.gov/universe/uni_matter.html)

WMAP determined that the universe is flat, from which it follows that the mean energy density in the universe is equal to the critical density.

This critical energy density is roughly one Joule per cubic kilometer, i.e. distinctively non-zero.

[Klaynos]

I don't know exactly all the contributions that are taken into account, but I was under the impression that the mainstream view is that the average energy density of the universe (and therefore the total energy) is distinctively non-zero. From the first random Google hit (http://map.gsfc.nasa.gov/universe/uni_matter.html)

This critical energy density is roughly one Joule per cubic kilometer, i.e. distinctively non-zero.

 

 

I would suggest that this is implied by the significant lack of antimatter in the universe, one of the unanswered puzzles of cosmology.

 

[All, please disregard this post, it was too early I think I was misremembering something which I cannot now make sense of]

Edited June 2, 2012 by Klaynos

[timo]

I have no idea what you are trying to say there, Klaynos. Surely, putting some anti-matter in the universe in addition to the matter that already is there would merely increase the energy density some more.

[juanrga]

I've recently been listening to some talks by Peter Atkins, a chemist and popular science writer, and I've heard him a couple of times talk about the beginning of the universe in terms of "nothing coming from nothing." This is because he says that current data in cosmology tentatively indicates that the universe might have a total energy of 0, and, therefore, the universe ought not be considered to be something coming from nothing, but nothing separating into its component, self-annihilating parts.

 

Is there a name for this theory in physics? Does it have many proponents? Can anyone elaborate on it for me?

 

This is sometimes named the free-lunch cosmology. It is an idea based in certain hypothetical models of quantum cosmology that assume that the total energy of universe is exactly zero. If the total energy is always zero then the creation of the universe would be a kind of transformation from something (preuniverse) with zero energy to something (universe) with zero energy (0 [math]\rightarrow[/math] 0). Some people goes beyond this speculation and claims that the universe was created out from 'nothing'. There is a popular book now about this, but is receiving very hard criticism (see this review).

 

I find it all odd. First, the original premises are based in some incorrect quantum cosmological models (I do not agree that the total energy of the Universe is zero). Second by 'nothing' that people means systems as a quantum vacuum or something similar.

Edited June 2, 2012 by juanrga

[Klaynos]

I have no idea what you are trying to say there, Klaynos. Surely, putting some anti-matter in the universe in addition to the matter that already is there would merely increase the energy density some more.

 

Neither do I now, early morning post trying to think about what I was trying to say is confusing me,

[MigL]

Arguments can be made for the total energy of the universe to be zero since the universe is expanding. By no means are these guesstimates accurate enough to say one way or the other. The biggest question mark is vacuum energy. A simple 'back of an envelope' calculation using simple harmonic oscillators and using the Planck scale as the cut-off yields a value which is 120 orders of magnitude higher than expected.

[timo]

Arguments can be made for the total energy of the universe to be zero since the universe is expanding.

What would that argument be?

 

By no means are these guesstimates accurate enough to say one way or the other.

Which guesstimates? And what are the inaccuracies?

[mississippichem]

This does not invalidate the premise of the OP but I would be weary of any physics speculation asserted by Atkins. Some of you may know that his textbooks have been a staple in undergraduate physical chemistry classes for some time. In the last few years the quality of his books have gone down hill IMO. Some of us in the p-chem world have begun to wonder whether or not he is getting senile in his old age. I can't seem to find anything now but he's made some less than rigorous statements about QM in recent times. Let's hope he doesn't go the way of Pauling (great chemist fading into crackpot obscurity). Again this does not automatically make anything he says incorrect but I thought this was worth mentioning. Consider the source but don't let ad hom. kill an idea.

[Polednice]

Yes, mississippichem - I enjoy listening to Atkins, but I could tell by his general demeanour that his descriptions might require a pinch of salt.

 

So, by the sounds of it, does this all play into Lawrence Krauss's recent book and the idea about an initial quantum fluctuation? Of course, I know about that - I didn't recognise from Atkins's description that he meant the same thing.

[MigL]

This is all rather speculative Timo, but the same vacuum energy which produced inflation shortly after the big bang obviously has a residual presence. We can call it 'dark energy' or a Cosmological constant, but some kind of 'negative' gravity is not only keeping expansion going, it is accelerating it. In GR it can be shown that a high pressure condition results in a negative energy/gravity condition. If I recall Guth's original inflation theory used a false vacuum energy condition due to symmetry breaking of a scalar ( Higgs ? ) field, but that has since been shown not to be the case.

In any case it all depends on getting a handle on the value of the vacuum energy, which as I said earlier, is way too high.

 

As to which and who's guesstimates, sorry but I'm passing the time at work and don't have references ready, I usually post retained info from various books I've read.

Edited June 2, 2012 by MigL

[granpa]

the reason the total energy is said to be zero is because gravitational potential energy is considered to be negative.

 

I also note that my posts have been deleted.

 

regardless of whether the total energy is zero or not, something cannot come from nothing.

 

there had to be something there to start with from which the universe sprang

[timo]

the reason the total energy is said to be zero is because gravitational potential energy is considered to be negative.

As I said previously, I don't know which contituents enter into the energy density calculations fitted on the WMAP results. So is your statement a guess of yours or a fact? And in either case, how is the potential energy calculated?

[granpa]

the energy density of any field is proportional to the square of the field intensity.

except that its negative for gravity and positive for electric and magnetic fields

 

http://en.wikipedia.org/wiki/Gravitational_energy

[timo]

This is all rather speculative Timo, but the same vacuum energy which produced inflation shortly after the big bang obviously has a residual presence. We can call it 'dark energy' or a Cosmological constant, but some kind of 'negative' gravity is not only keeping expansion going, it is accelerating it.

Dark energy has a negative pressure but positive energy component. In fact, it makes up the most of the (positive) energy in the universe. Calling it "vacuum energy" is problematic, btw (for the reason that it doesn't fit to QFT vacuum energy expectations, as you already mentioned).

 

In GR it can be shown that a high pressure condition results in a negative energy/gravity condition.

Got a reference on that? I don't even understand what that is supposed to mean.

 

the energy density of any field is proportional to the square of the field intensity.

except that its negative for gravity and positive for electric and magnetic fields

 

http://en.wikipedia.org/wiki/Gravitational_energy

I'm not completely convinced that electrodynamics in a static spacetime is the proper approach for general relativity on scales of the universe. In fact, adding a link to a Wikipedia article saying "in general relativity gravitational energy is extremely complex, and there is no single agreed upon definition of the concept" makes your statement somewhat dubious. EDIT: Oh, and you haven't answered the question whether the thing with the gravitational energy is a well known fact or just a random guess of yours. Edited June 3, 2012 by timo

[MigL]

Have that reference for you now Timo.

Abook called COSMOLOGY, INFLATION AND the PHYSICS of NOTHING by William H Kinney of the department of strings, physics and cosmology at Columbia university. I believe section 2.4 ( pg 13 ) The Vacuum In Quantum Field Theory deals with vacuum energy calculations and the relation between pressure and gravity is explored in another section ( sorry did not look that one up ).

An interesting book if you have access to it ( I have an e-book ).

[granpa]

actually my posts were not deleted.

I confused this thread with a similar one on another forum

[timo]

Have that reference for you now Timo.

A book called COSMOLOGY, INFLATION AND the PHYSICS of NOTHING by William H Kinney of the department of strings, physics and cosmology at Columbia university. I believe section 2.4 ( pg 13 ) "The Vacuum In Quantum Field Theory" deals with vacuum energy calculations. An interesting book if you have access to it ( I have an e-book ).

You presumably talk about this: http://arxiv.org/abs/astro-ph/0301448 . It's not a book but a script for a mini lecture series. Being on arXiv, everyone has access to it - including me. I do see the mainstream calculation for the vacuum energy in naive QFT in section 2.4. But that's not what I asked for - you can find that in pretty much every intro text on QFT. The statement I wondered about is the claim that high pressure can result in negative gravity or negative energy. I searched the text for the keyword "negative", and all I could find was "negative curvature" and "negative pressure". Have you possibly been confused by dark energy's weird property of having negative pressure?

Edited June 3, 2012 by timo

[MigL]

Sorry Timo, I went back and realised my mistake. The phrase "In GR it can be shown that a high pressure condition results in a negative energy/gravity condition" should have read as "In GR it can be shown that a high negative pressure condition results in a negative energy/gravity condition". It needs to be highly negative pressure because it needs to overcome gravitational attraction before it can start acting like a Cosmological constant or a cause for inflation.

The same Kinney lecture notes have a brief explanation of this at the beginning of section 2,5, pg 15.

[timo]

I cannot see where in chapter 2.5 "a high negative pressure condition results in a negative energy/gravity condition". It is true that the negative so-called pressure component of the cosmological constant drives the expansion of the universe. I agree that this is not what one naively expects gravity to do, so I would also agree that one may loosely think of it as "negative gravity" - it's most certainly not what it would be called in a professional environment, though. However, if I understand you and the Kinney text correctly, then you seem to equate your already dubious "negative gravity" with "negative energy". That I object to.

 

I assume the reason is that you heard statements like "in general relativity, the source of gravity is energy": This is not fully correct. In fact the first equation in chapter 2.5 may be a good counter example, as it gives the reaction of spacetime [math]\ddot a / a[/math] (i.e. some gravitational effect) depending energy density [math]\rho[/math] and so-called pressure contribution [math]3w\rho[/math].

[MigL]

That equation you spoke of (49) is merelyl the acceleration in terms of the equation of state.

The third line below that states

"But we have seen that a cosmological constant has the odd property of negative pressure, w=-1,so that a universe dominated by vacuum energy actually expands faster and faster with time"

 

Now negative gravity might not be a 'professional' term but what should I be using , repulsion, anti-gravity, expansion, inflation ??? The fact remains that a negative vacuum pressure which is over a certain threshold, will ovecome the normal gravitational attraction, and actually start 'expanding' space-time like the cosmological constant and inflation do.

 

Someone once said if you can't explain something in simple terms, the you don't understand it. So let me know how I do.

Consider a spring and put pressure on it. This usually compresses the spring but we'll disregard this effect. The pressurised spring has more energy, and if you were willing to do an accurate enough calculation you would find that it actually weighs a miniscule amount more it will, in effect, have a slightly greater effect on the space-time curvature around it and therefore a stronger gravitational well. If you then remove pressure from the spring, you are actually removing energy from the system with the resultant less space-time curvature and less gravity.

Now consider the vacuum, it has the same compressibility as the spring with the exception that negative pressure on the spring actually stretches it and again gives it more energy. The vacuum instead, can have more and more negative pressure and keep losing more and more energy. Since the system in this case is not the spring but the vacuum of all space-time, it is all space-time whose energy is becoming more and more negative. If I remember correctly from one of DrR admonishments, GR does not have the condition of conservation of mass-energy ( during a discusiion of Noether's theorem).

Edited June 4, 2012 by MigL

[timo]

That equation you spoke of (49) is merely the acceleration in terms of the equation of state.

So?

 

Now negative gravity might not be a 'professional' term but what should I be using , repulsion, anti-gravity, expansion, inflation?

"Accelerated expansion of the universe" would be a good choice in the case that you speak about the accelerated expansion of the universe (it is not exactly easy to figure out what you are talking about).

 

The fact remains that a negative vacuum pressure which is over a certain threshold, will ovecome the normal gravitational attraction, and actually start 'expanding' space-time like the cosmological constant and inflation do.

At least when it comes to the time behavior of length scales in an Friedman-Robertson-Walker universe and the idea that gravity must cause the universe to contract. That's never been questioned in this thread.

 

Someone once said if you can't explain something in simple terms, the you don't understand it. So let me know how I do.

That statement which is often attributed to Einstein does not imply that the usage of pseudo-analogies equates with an understanding. Neither does appealing to quotes of Einstein itself. You know yourself that you never took a proper course in general relativity (or at least cosmology). Why would it need me to explicitly tell you how you are doing? I've not bothered thinking through your spring example for reasons given below.

 

You are correct that GR does not necessarily conserve energy: Given a suitable mapping between volumes at different times it constantly increases due to the constant positive energy density contribution of dark energy. I've mentioned that the energy contribution of dark energy is positive multiple times in this thread, I have given a link to a NASA page, I have even tried explained it to you on your beloved lecture notes (on "merely the acceleration in terms of the equation of state", which happens to be one of the fundamental relations in cosmology). We've just met the point where I am annoyed with this discussion (bordering to "sick of it").

 

Above may be a bit harsh. No offense meant, though. But this thread appears to become a huge waste of time for me. Maybe next time we meet on this forum will turn out better.

[robheus]

Zero nett energy does not equal "nothing"

[Aethelwulf]

I've recently been listening to some talks by Peter Atkins, a chemist and popular science writer, and I've heard him a couple of times talk about the beginning of the universe in terms of "nothing coming from nothing." This is because he says that current data in cosmology tentatively indicates that the universe might have a total energy of 0, and, therefore, the universe ought not be considered to be something coming from nothing, but nothing separating into its component, self-annihilating parts.

 

Is there a name for this theory in physics? Does it have many proponents? Can anyone elaborate on it for me?

 

Yes, it is called the Null Energy Condition.

 

[math]Mc^2 - \frac{GM^2}{2R} = E[/math]

 

When [math]M=0[/math] it is said you are left with the metric.