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Author Topic: Is the universe flat for a second reason?  (Read 1989 times)

Offline namaan

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Is the universe flat for a second reason?
« on: 06/11/2010 19:36:22 »
Hey folks,

I've read about how the universe is flat and the experiments that lead to this conclusion as well. What do you think of the following being another reason for the universe's flatness?

I read some where on these forums about "4d black holes", and have the general impression that as 4d space is bent by mass, mass follows the curvature. This suggests to me that all mass is actually defined in 4 dimensions. But if this is the case, then doesn't the fact that collisions between 4d masses consistently occur in a 3 dimensional manner require a flat definition of spacetime? In other words, an extreme flatness of spacetime could force 4d masses to interact within a single thin 3d slice.

I think this also suggests a possible mechanism for quantum tunneling. If fundamental particles that are small enough collide with enough momentum along this 3d slice, then like billiard balls hitting each other fast enough, one might just skip over the other.
« Last Edit: 06/11/2010 19:39:32 by namaan »


 

Offline QuantumClue

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Is the universe flat for a second reason?
« Reply #1 on: 15/11/2010 09:35:30 »
There is only one main reason why the universe appears to be flat, and that is due to the inflationary phase.
 

Offline QuantumClue

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Is the universe flat for a second reason?
« Reply #2 on: 15/11/2010 09:36:28 »
I suppose you could also say the Cosmological Constant is near zero, but if inflation did not occur, then the universe would not have been ironed out.
 

Offline Pikaia

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Is the universe flat for a second reason?
« Reply #3 on: 16/11/2010 00:14:00 »
Curvature of spacetime is just another word for gravity - in General Relativity they are regarded as the same thing.

For spacetime to be curved you need mass/energy to produce gravity, but according to the Law of Conservation of Energy, mass/energy cannot be created. So the total mass/energy of the Universe is zero, and the curvature of spacetime must therefore be zero (on a large scale). The energy of the matter within the Universe is balanced by the negative energy of its gravitational field, giving a total of zero.

So you do not need inflation to explain the flatness of spacetime, only the Law of Conservation of Energy.
 

Offline QuantumClue

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Is the universe flat for a second reason?
« Reply #4 on: 16/11/2010 05:39:36 »
Curvature of spacetime is just another word for gravity - in General Relativity they are regarded as the same thing.

For spacetime to be curved you need mass/energy to produce gravity, but according to the Law of Conservation of Energy, mass/energy cannot be created. So the total mass/energy of the Universe is zero, and the curvature of spacetime must therefore be zero (on a large scale). The energy of the matter within the Universe is balanced by the negative energy of its gravitational field, giving a total of zero.

So you do not need inflation to explain the flatness of spacetime, only the Law of Conservation of Energy.

Yes inflation is required. http://www.google.co.uk/search?q=inflation+caused+flatness&rls=com.microsoft:en-us:IE-SearchBox&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7TSEH_enGB381GB381
« Last Edit: 16/11/2010 05:42:34 by QuantumClue »
 

Offline QuantumClue

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Is the universe flat for a second reason?
« Reply #5 on: 16/11/2010 05:45:30 »
Curvature of spacetime is just another word for gravity - in General Relativity they are regarded as the same thing.

For spacetime to be curved you need mass/energy to produce gravity, but according to the Law of Conservation of Energy, mass/energy cannot be created. So the total mass/energy of the Universe is zero, and the curvature of spacetime must therefore be zero (on a large scale). The energy of the matter within the Universe is balanced by the negative energy of its gravitational field, giving a total of zero.

So you do not need inflation to explain the flatness of spacetime, only the Law of Conservation of Energy.

Yes inflation is required. http://www.google.co.uk/search?q=inflation+caused+flatness&rls=com.microsoft:en-us:IE-SearchBox&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7TSEH_enGB381GB381

See what you said is basically the same as accepting there is very little curvature in spacetime, therefore you conclude niavely then that energy must be zero. It is true that when you add positive and negative matter together it produces a zero result, but that is because to every positive particle in the vacuum there is a corresponding particle with negative energy in the vacuum. More concisely in the words of GR is that the CC is near zero. However, inflation played a bigger role in the early universe in the geometry of the vacuum
 

Offline Pikaia

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Is the universe flat for a second reason?
« Reply #6 on: 16/11/2010 10:25:44 »
See what you said is basically the same as accepting there is very little curvature in spacetime, therefore you conclude niavely then that energy must be zero.
No it is the other way round. Total energy must be exactly zero because of the conservation of energy. It follows that the average curvature must be exactly zero. This is confirmed by observation, so I still do not see any need for inflation.
 

Offline QuantumClue

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Is the universe flat for a second reason?
« Reply #7 on: 16/11/2010 10:36:44 »
See what you said is basically the same as accepting there is very little curvature in spacetime, therefore you conclude niavely then that energy must be zero.
No it is the other way round. Total energy must be exactly zero because of the conservation of energy. It follows that the average curvature must be exactly zero. This is confirmed by observation, so I still do not see any need for inflation.

That depends. In special relativity, the energy momentum tensor is seen as a zero quantity and as a conservation law. However, one cannot draw that the energy momentum tensor is a conservation law in GR if memory serves. Secondly, there might have been a lot of surviving curvature if inflation did not occur. Inflation literally ''dilluted'' matter in our universe, giving it its increadible flatness.
 

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Is the universe flat for a second reason?
« Reply #7 on: 16/11/2010 10:36:44 »

 

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