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Hawking on Universe Created from Nothing


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Another question on Hawking and Mlodinow's book, The Grand Design. On page 180, they state:

 

"Because gravity is attractive, gravitational energy is negative . . . This negative energy can balance the positive energy needed to create matter."

 

Then they state:

 

"Because gravity shapes space and time, it allows space-time to be locally stable but globally unstable. On the scale of the entire universe, the positive energy of the matter can be balanced by the negative gravitational energy, and so there is no restriction on the creation of the entire universe."

 

I understand that per general relativity, gravity is a global effect. Because gravity (spacetime curvature) is effectively uniform in magnitude and direction over a local region of spacetime, one cannot detect the effects of gravity locally. That is over a small enough space and over a small enough time. Here all particles experience the same acceleration amount and direction. So in the reference frame of one of these particles. all other particles in this local region are at rest. But globally, the magnitude and/or direction of gravity does change, so we can detect its effects over a global region of spacetime, e.g. tidal forces.

 

But what do they mean by "spacetime is locally stable but globally unstable? Please enlighten me.

Edited by I ME
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But what do they mean by "spacetime is locally stable but globally unstable? Please enlighten me.

 

Galaxies, solar systems, and planets don't fall apart. But distant galaxies are receding from each other at faster than the speed of light, and will no longer be in each other's sphere of influence in the least (falling out of the observable universe).

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Galaxies, solar systems, and planets don't fall apart. But distant galaxies are receding from each other at faster than the speed of light, and will no longer be in each other's sphere of influence in the least (falling out of the observable universe).

 

OK, so what does this so-called instability at cosmic scales have to do with Hawking's point that the universe can be created out of nothing?

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OK, so what does this so-called instability at cosmic scales have to do with Hawking's point that the universe can be created out of nothing?

I think he is arguing that if the net sum of energy in the Universe is zero then it's creation wouldn't violate the conservation law.

 

"The law of conservation of energy is an empirical law of physics. It states that the total amount of energy in an isolated system remains constant over time (is said to be conserved over time). A consequence of this law is that energy can neither be created nor destroyed: it can only be transformed from one state to another. The only thing that can happen to energy in a closed system is that it can change form: for instance chemical energy can become kinetic energy.

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

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I think he is arguing that if the net sum of energy in the Universe is zero then it's creation wouldn't violate the conservation law.

 

"The law of conservation of energy is an empirical law of physics. It states that the total amount of energy in an isolated system remains constant over time (is said to be conserved over time). A consequence of this law is that energy can neither be created nor destroyed: it can only be transformed from one state to another. The only thing that can happen to energy in a closed system is that it can change form: for instance chemical energy can become kinetic energy.

http://en.wikipedia....onservation_law

 

Ya, I think that's it! Thanks. (I love this forum)

 

Oh, I have another point to discuss. So the total amount of gravity (spacetime curvature) in the universe is equal to the total amount of mass/energy in the universe. Here by mass/energy I mean all the matter (ordinary and dark) and all the energy (including dark energy). Is this because the overall mass/energy density of the universe is the so-called critical value; implying a flat spacetime curvature? But here we are talking only about the observable universe. Per inflationj theory, our visible universe looks flat (and nearly uniform) because it is a miniscule part of a much much greater universe which expanded exponentially just after the big bang.

 

So my question: Hawking is saying that this overall gravitation energy (negative) of the universe equals the overall mass/energy of the universe (positive); so the net energy is zero. Does this apply only to the observable universe or the entire universe? And if it applies to the entire universe, how do physicists know about something beyond what we can observe? What extrapolation are they making?

 

Any thoughts on this would be greatly appreciated.

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And if it applies to the entire universe, how do physicists know about something beyond what we can observe? What extrapolation are they making?

We only have direct knowledge of the observable universe, but according to the Cosmological Principle the entire Universe should not be radically different and as such it is predicted to look the same on large scales with equal structures and uphold the same laws of physics.

 

In modern physical cosmology, the cosmological principle is the working assumption that observers on Earth do not occupy a restrictive, unusual or privileged location within the universe as a whole, judged as observers of the physical phenomena produced by uniform and universal laws of physics. As astronomer William Keel explains:

 

"The cosmological principle is usually stated formally as 'Viewed on a sufficiently large scale, the properties of the Universe are the same for all observers.' This amounts to the strongly philosophical statement that the part of the Universe which we can see is a fair sample, and that the same physical laws apply throughout. In essence, this in a sense says that the Universe is knowable and is playing fair with scientists."

 

The cosmological principle contains three implicit qualifications and two testable consequences.

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

Edited by Spyman
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We only have direct knowledge of the observable universe, but according to the Cosmological Principle the entire Universe should not be radically different and as such it is predicted to look the same on large scales with equal structures and uphold the same laws of physics.

 

 

I understand all that (or at least I think I do). But here's my point.

 

Visible Universe: Observations tell us that the overall spacetime curvature for the visible universe is zero, i.e. a flat configuration. This says that the overall gravitational energy is balanced by rest of the overall mass/energy. But what we observe is a tiny portion of the overall universe.

 

Unobserved Universe. The unobserved universe beyond what we can see may or may not be a flat configuration. It could have a net positive or net negative spacetime curvature. In fact, a non-zero curvature is most likely. So the unobserved universe most probably does not have a flat configuration. (It is closed or open.) Does this say that for the overall unobserved universe, gravitational energy does not balance the rest of mass/energy?

 

That is my question. Am I oversimplifying here? Please advise.

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I understand all that (or at least I think I do). But here's my point.

 

Visible Universe: Observations tell us that the overall spacetime curvature for the visible universe is zero, i.e. a flat configuration. This says that the overall gravitational energy is balanced by rest of the overall mass/energy. But what we observe is a tiny portion of the overall universe.

 

Unobserved Universe. The unobserved universe beyond what we can see may or may not be a flat configuration. It could have a net positive or net negative spacetime curvature. In fact, a non-zero curvature is most likely. So the unobserved universe most probably does not have a flat configuration. (It is closed or open.) Does this say that for the overall unobserved universe, gravitational energy does not balance the rest of mass/energy?

 

That is my question. Am I oversimplifying here? Please advise.

 

You are observing cats. All cats have 4 legs. So you are concluding that cats that you cannot see have 5 legs. Does that make sense?

In other words, why should the unobservable universe be different from the one we are observing?

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In fact, a non-zero curvature is most likely.

If the curvature was totally random then it would be very unlikely that it was exactly zero, but then it would also be hard to explain why it got so close to zero, even if it of course could be a pure coincidence.

 

If there is a rational explanation of how it got to be this value, if the curvature was determined in a scientific event, then it is no longer totally random and without any understanding of this process we are not able to make conclusions of which value is more or less likely to occur.

 

Speculations that "the universe can and will create itself from nothing" while the physical laws, that we can observe today, are valid and rules, should logically predict that energy needs to be balanced to zero for the entire Universe.

 

The overall geometry of our observable universe is nearly zero, but if the whole Universe is much much larger than our observable part, then we might still measure a flat spacetime locally due to inaccuracy in our instruments, even if the total Universe could be of slightly positive or negative curvature.

 

Hawking seems to advocate that the Universe was created in a physical process at the Big Bang and while better measurements of the spacetime curvature in the future might show him wrong or strengthen his view, at the moment it falls within the tolerance level of our observations.

Edited by Spyman
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If the curvature was totally random then it would be very unlikely that it was exactly zero, but then it would also be hard to explain why it got so close to zero, even if it of course could be a pure coincidence.

 

 

 

The fact that the observable universe happens to appear flat is a very unlikely outcome. Physicists were at a loss to explain why this so unlikely outcome of nearly zero net spacetime curvature is so. Until Guth's inflation theory. Guth's theory says that the universe expanded exponentially about 10**-32 seconds after the big bang. This great expansion is given as the reason why we see a flat universe. Even though the entire universe is most likely not exactly flat, the expansion makes the region we see flat.

 

It is like on the Earth. The Earth is curved , but an ant on a football feild thinks that it is flat because he/she is seeing only a very small portion of the curved surface.

 

Per Wikipedia link http://en.wikipedia....tion_(cosmology) :

 

"As a direct consequence of this expansion, all of the observable universe originated in a small causally connected region. Inflation answers the classic conundrum of the Big Bang cosmology: why does the universe appear flat, homogeneous and isotropic in accordance with the cosmological principle when one would expect, on the basis of the physics of the Big Bang, a highly curved, heterogeneous universe?"

 

So that's my point. The observable part of the universe is flat. The entire universe is most likely highly curved. Is Hawking's net zero energy of the universe concept based on a flat universe? If so, it is wrong, because only the part of the universe we can see is flat. THe entire unseen universe is most likely highly curved.

 

I need help hear to know whether Hawking's idea on zero net energy is based on a flat universe or if it has nothing to do with it.

 

You are observing cats. All cats have 4 legs. So you are concluding that cats that you cannot see have 5 legs. Does that make sense?

In other words, why should the unobservable universe be different from the one we are observing?

 

You are standing on the sidelines observing the surface of a football field. It appears flat. This is your observable universe. You conclude the entire Earth is flat. But the entire Earth is highly curved. And if you rise high into outer space, you see the entire Earth and know it is not flat. Similarly, the entire unobserved universe may or may not be flat. In fact, cosmologists believe it is highly curved.

Edited by I ME
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What about the energy required to generate the mass of the universe and to displace the volume that the universe displaces? The energy balance seems to consider gravitation and kinetic energy but I don't see an accounting of internal energy (enthalpy).

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So that's my point. The observable part of the universe is flat. The entire universe is most likely highly curved. Is Hawking's net zero energy of the universe concept based on a flat universe? If so, it is wrong, because only the part of the universe we can see is flat. THe entire unseen universe is most likely highly curved.

 

I need help hear to know whether Hawking's idea on zero net energy is based on a flat universe or if it has nothing to do with it.

From my understanding of General Relativity, a totally empty space volume, without quantum fluctuations and radiation so that it is a perfect true vacuum, would be exactly flat and as such I think if introducing a field of negative energy balancing against matter and normal energy would together keep space flat on average, but locally gravity would curve space and on larger scales negative energy would accelerate expansion.

 

Therefore my personal guess, without reading the book and with limited understanding of relativity, is that Hawking's idea is based on a flat Universe.

 

 

Before the discovery of Dark Energy the shape of the Universe cold either be closed as curved inward, flat or open as curved outward but with Dark Energy the Universe can have any shape and still be open or closed. A curved inward universe could still feature an accelerating expansion and be open and so could also a flat universe with Dark Energy.

 

The Universe is expanding with an accelerating rate which would indicate that it is open but the overall geometry of space could still be flat.

 

Flat universe

If the average density of the universe exactly equals the critical density so that Ω=1, then the geometry of the universe is flat: as in Euclidean geometry, the sum of the angles of a triangle is 180 degrees and parallel lines continuously maintain the same distance.

 

Absent dark energy, a flat universe expands forever but at a continually decelerating rate, with expansion asymptotically approaching a fixed rate. With dark energy, the expansion rate of the universe initially slows down, due to the effect of gravity, but eventually increases. The ultimate fate of the universe is the same as an open universe.

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

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From my understanding of General Relativity, a totally empty space volume, without quantum fluctuations and radiation so that it is a perfect true vacuum, would be exactly flat and as such I think if introducing a field of negative energy balancing against matter and normal energy would together keep space flat on average, but locally gravity would curve space and on larger scales negative energy would accelerate expansion.

 

Therefore my personal guess, without reading the book and with limited understanding of relativity, is that Hawking's idea is based on a flat Universe.

 

Thanks, Spyman. If your guess is right; then, as I said, then maybe Hawking is wrong. The visible universe is flat, but cosmologists think the entire univere is most likely highly curved (see earlier link). I wonder what the balance or non-balance of gravity and matter/energy is in a highly curved universe?

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Now I'm doing a reply to my reply. This thing has really got my interest! I did a google search on "Flat Universe Net Zero Energy" and the results were consistent. It appears, as Spyman said, that the net zero energy universe IS for a net flat curvature universe. But per inflation theory, the reason we see a flat observable universe is because the highly curved overall universe expanded exponentially moments after the Big Bang (inflation). So its like blowing up a balloon to stupendous size. We ants on its surface see only a very small portion of this balloon. And so, to us, the part we can see appears to be flat. But the entire balloon universe is still highly curved. So the net energy of the entire universe IS NOT ZERO. All these conclusions from Hawking and others is based on only the portion of the universe that we can see.

 

So Hawking's proposal does NOT apply to the entire universe.

 

Is there something I am missing in my argument?

 

 

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There is energy within gravitational potential. I can place a tank of water at a height H, and take out energy, as the water falls to lower potential. But say I didn't take that energy out when the water fell. According to the conservation of energy, it had to go somewhere to be conserved.

 

Say we have gravity acting on a cloud of stella gas, compacting the mass so the local space-time contracts. According to the conservation of energy, the lowering of gravity potential gives off energy that we can convert to alternate energy if we had the technology. One possible place to store at least some of that energy, to maintain energy conservation, is within contracting space-time. That may be why in SR we need to add energy to get similar effects in space-time. The energy potential within contracted space-time, adds potential in time. If the energy output, stemming from gravity lowering potential, goes into rotation of the cloud, it takes longer for the mass to condense into a clump, so contacting space-time gets potential slower.

 

Based on this logic, the expansion of space-time should do the opposite. It needs to give off energy. In SR, the proper direction is obvious since the kinetic energy lowers (energy has to be given off) for space-time to expand. Based on energy conservation, the energy output due to the expansion of space-time needs to go somewhere. One place some of it can go is within entropy.

 

As an example. Say we had two identical factories making widgets, both with one error every 1000 seconds, on the average. One factory is in contracted space-time and the other in expanded space-time. The one that is in the expanded reference has time moving faster so will can make errors (entropy) quicker (when looked at side by side).

 

If you look at entropy, entropy needs energy to increase. Say you increased entropy but without energy being present. This would create negative energy. This is not suppose to happen, since it needs energy, so if it did, it would create an energy deficit or negative energy. Say instead we expanded space-time, but without energy given off. Since the expansion of space-time gives off energy, if energy was not given off, this would also create negative energy. To balance this off to retain zero energy, we would need to create energy. We can create potential energy, if we contracted space-time. If they form together they can cancel at zero energy.

 

What we now have is a potential that equals zero energy. The fastest way to remove that potential is not for expanded and contracted space-time to pull together, but to create mass/energy gravity to fill in the negative energy of expanded space-time so it equals zero. We also need to add entropy with negative energy at the contracted space-time to zero there. The mass/energy/gravity will cause the expanded space-time to contract, while the negative energy entropy will cause contracted space-time to expand. We can maintain zero energy while creating two effects, one which makes mass appear to contract and the other makes entropy continues to expand.

Edited by pioneer
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If the universe began from nothing, which somehow had the tendency to differentiate into positive and negative energy, what would have caused the potential to differentiate in this way in the first place? The only thing I can think is that maybe all forces emerge as distinct from one another due to the entropy of expansion. In other words, gravity field-force may have been so condensed at the point of the big bang, that it was indistinguishably strong from the other types of force. As such, maybe gravity and the other forces began to differentiate as spacetime emerged from the expansion, since this would have allowed some parts of the field to fragment into particles of matter and others into residual gravitational field-force extending beyond the matter. But still, what would have caused such an intense lump of field-force to form in the first place and why would it expand? Is force itself an eternal fixture of existence or does it have a defined life including birth and death? My guess would be that it is born as strong nuclear force, which degenerates into weak nuclear force leading to primordial fissionary fragmentation of the initial macro-atom into increasingly smaller particles. As these particles stabilized under their remaining strong nuclear force, they were in (heat) motion relative to each other which resulted in expansion and radiation. So, EM radiation is the product of dying force, which dissipates to an ultimate volume of spacetime. If the big bang began with such a single unified macro-atom, it seems to me that such an atom would be the product of a black-hole capturing a great deal of matter-energy, and that the residual EM radiation of the universe could ultimately condense under its own gravity and form such a black hole again and start another big bang. Still, why would a black hole evolve internally into a spacetime-expanding fragmenting universe of matter-energy? Would it do this just because nothing has any way of escaping therefore it has to propagate internally in some way just b/c it contains energy?

Edited by lemur
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