# why is dark energy necessary?

by gregtomko
Tags: acceleration, dark energy, universe
 P: 71 If the mass of the universe is constantly being converted to energy through nuclear fusion, and nothing can travel outside of space-time, then isn't the ratio of energy to mass increasing? If so, then wouldn't the only possible option be for an acceleration of the universe's expansion?
 P: 71 Sorry if this was a stupid question. It just occurred to me that maybe the extra energy would be converted to mass in the form of the extra velocity of the matter in the universe. Maybe this cancels out the lost mass that used to be stored in the binding energy, which was released by the nuclear fusion. Is that it?
 Sci Advisor P: 5,776 Stars shine in all directions, so the energy can't be translated into a single direction.
P: 71

## why is dark energy necessary?

 Quote by mathman Stars shine in all directions, so the energy can't be translated into a single direction.
Stars shine their energy through space-time...
Please explain your reference to "energy can't be translated into a single direction" , I don't understand, what direction are you referring to?
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 Quote by gregtomko If the mass of the universe is constantly being converted to energy through nuclear fusion, and nothing can travel outside of space-time, then isn't the ratio of energy to mass increasing? If so, then wouldn't the only possible option be for an acceleration of the universe's expansion?
I don't follow your logic at all. How would you propose that the reactions taking place inside stars creates an effect that spreads out evenly throughout the universe and causes the creation of space. I REALLY don't see how you get from one to the other.
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 Quote by gregtomko Sorry if this was a stupid question. It just occurred to me that maybe the extra energy would be converted to mass in the form of the extra velocity of the matter in the universe. Maybe this cancels out the lost mass that used to be stored in the binding energy, which was released by the nuclear fusion. Is that it?
I think not. By what process would that happen?
P: 71
 Quote by phinds How would you propose that the reactions taking place inside stars creates an effect that spreads out evenly throughout the universe and causes the creation of space.
 Quote by Chronos By what process would that happen?
The energy released through fusion has to go somewhere. Stars radiate their energy reasonably uniformly as far as I know. As the energy is released from the stars they lose mass. All stars are doing this, and they have been for quite some time. Since there is no space-time outside of the matter in the universe, that energy is contained inside the confines of that matter. I know I am not an astrophysicist, thats why I am asking the question.

When particles are hit by photons, the particles get pushed slightly, if I am not mistaken. That energy keeps bouncing around, or being absorbed and then radiated, until it eventually is converted through those slight pushes on particles into mass again, in the form of velocity.

The question is, with less mass over time, and more energy over time, why wouldn't acceleration be expected?

Thanks for your replys phinds and Chronos, I can use all the help I can get :-)
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 Quote by gregtomko ... When particles are hit by photons, the particles get pushed slightly, if I am not mistaken. That energy keeps bouncing around, or being absorbed and then radiated, until it eventually is converted through those slight pushes on particles into mass again, in the form of velocity. ...
But the expansion of space is NOT "pushing" on anything, it's just creating space, which creates more distance between objects that are not gravitationally bound.

The whole MECHANISM of "dark energy" just isn't what you seem to think it is.
P: 71
 Quote by phinds the expansion of space is NOT "pushing" on anything, it's just creating space, which creates more distance between objects that are not gravitationally bound.
That is what I am saying. The photons released from the stars have a net effect of pushing against the other particles in the universe. The stars are all pushing against each other, and also against whatever other matter is around them. When a photon from one star hits a particle in another star, that is energy which helps to create more distance between them. The expansion of space is the particles pushing against each other, using the bonding energy released by nuclear fusion.
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 Quote by gregtomko That was what I am saying. The photons released from the stars have a net affect of pushing against the other particles in the universe. The stars are all pushing against each other, and also against whatever other matter is around them. When the photon from one star hits another particle in another star, that is energy which helps to create more distance between them. The expansion of space is the particles pushing against each other, with the bonding energy released by nuclear fusion.
As far as I'm aware there is no evidence to support this conjecture. LOTS of smart physicists have spent a lot of time trying to figure out what dark energy is and I don't find it believable that they have overlooked such a straightforward explanation.
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 Quote by phinds As far as I'm aware there is no evidence to support this conjecture. LOTS of smart physicists have spent a lot of time trying to figure out what dark energy is and I don't find it believable that they have overlooked such a straightforward explanation.
The OP isn't asking about dark energy though right? Just regular ol' run of the mill energy. He's proposing that dark energy doesn't exist.
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 Quote by dacruick The OP isn't asking about dark energy though right? Just regular ol' run of the mill energy. He's proposing that dark energy doesn't exist.
There is SOMETHING that causes the creation of space in between galaxies and thus causes an accelerating expansion of the universe. We call that something "dark energy" which is shorthand for "we have not a CLUE what is causing this". We see the effects, and as I said, lots of physicists spend lots of time thinking about what the hell it IS. There's a Nobel Prize in there for whoever figures it out first.

The OP is suggesting that the accelerating expansion is not due to dark energy but is a result of a mechanism using existing mechanics that causes the stars to push against each other and that THIS causes the accelerating expansion. This completly overlooks the fact that in a universe with all the stars pushing against each other, none of them move as a result at all, much less expand, much less have an accelerating expansion. It just doesn't work.
 P: 71 Right, I am just asking if there is all this energy being released by the stars, which would have to have an effect of expanding the universe, why is another form of energy needed? Unless all the energy of all the stars through all of time just isn't enough?
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 Quote by gregtomko Right, I am just asking if there is all this energy being released by the stars, which would have to have an effect of expanding the universe, why is another form of energy needed? Unless all the energy of all the stars through all of time just isn't enough?
But it WOULDN'T have that effect. What makes you think it would? What is the evidence?
P: 71
 Quote by phinds There is SOMETHING that causes the creation of space in between galaxies and thus causes an accelerating expansion of the universe. We call that something "dark energy" which is shorthand for "we have not a CLUE what is causing this". ........ This completly overlooks the fact that in a universe with all the stars pushing against each other, none of them move as a result at all, much less expand, much less have an accelerating expansion. It just doesn't work.
I thought they were moving away from each other, and thats why we need dark energy in the first place.
 PF Patron P: 4,983 our posts 12 and 13 crossed. What do you say to what I pointed out in post 12 ?
 P: 71 That when a photon is released from one particle, and hits another particle, it causes the two to be pushed slightly apart.
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 Quote by gregtomko I thought they were moving away from each other, and thats why we need dark energy in the first place.
They are moving away from each other apparently as a result of the big bang. The velocity is ACCELERATING and that is what is attributed to dark energy. That is, dark energy is NOT why is causing the expansion of the universe, it is what's causing the expansion to accelerate.

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