Is Dark Energy Necessary for the Acceleration of the Universe's Expansion?

[gregtomko]

In the future try to understand the subject more before shooting down someone who has actually done the math.

So you have done the math? I thought that nobody has ever done the math to explain dark matter, isn't that the whole point?

 

[Drakkith]

"Saying the "dark forces" appear stronger further out implies that the actual force of gravity or expansion increases as distance increases."

That relationship. That is an odd conclusion.

I don't see how. That is exactly the conclusion your statement brings me to.

So you have done the math? I thought that nobody has ever done the math to explain dark matter, isn't that the whole point?

I've done the math for a little bit of radiation pressure. I don't even know what you want to know about dark matter and energy that hasn't already be said. I think you should read up on dark matter and energy on wikipedia. You seem to have some misconceptions that could be cleared up by those articles.

 

[Chronos]

Dark matter does not clump. The dark matter haloes believed to surround galaxies are diffuse, but, there is so much of it [compared to baryonic matter], it need not be very dense to have a profound gravitational influence.

 

[gregtomko]

That is exactly the conclusion your statement brings me to.

I am not trying to draw a conclusion, just ask a simple question.

I don't even know what you want to know about dark matter and energy that hasn't already be said.

All I would like to know is the ratio of energy released from stars through fusion, to that needed for the acceleration of the expansion of the universe. If you could point me to that particular wikipedia page I would appreciate it.

 

[Drakkith]

All I would like to know is the ratio of energy released from stars through fusion, to that needed for the acceleration of the expansion of the universe. If you could point me to that particular wikipedia page I would appreciate it.

There isn't one because it isn't possible for radiation pressure to cause the expansion of the universe. You can't even calculate the "needed energy" because the two effects aren't even related. Radiation pressure would never result in galaxies receding from us greater than the speed of light, only expansion of space will do that.

 

[phinds]

There isn't one because it isn't possible for radiation pressure to cause the expansion of the universe. You can't even calculate the "needed energy" because the two effects aren't even related. Radiation pressure would never result in galaxies receding from us greater than the speed of light, only expansion of space will do that.

I've been trying to tell him that for several posts now, but for some reason he doesn't want to believe it.

 

[gregtomko]

Not the radiation pressure, just the straight a = F/m

 

[gregtomko]

Or is that what I am missing? Is the radiation pressure equal to the total energy released from stars?

 

[Drakkith]

Not the radiation pressure, just the straight a = F/m

Or is that what I am missing? Is the radiation pressure equal to the total energy released from stars?

Energy is released from stars as both EM radiation and as Neutrinos. Neutrinos interact so weakly with matter that they effectively do nothing in regards to our discussion. EM radiation is where radiation pressure comes from. The solar wind is another way that a Star loses energy/mass, however the effect is even less than the radiation pressure, especially over large distances.

 

[gregtomko]

Thanks for your reply Drakkith, it didn't seem right that radiation pressure could account for all energy released from stars. The basic reason for this post in the first place, is that I am curious about the amount of energy released from stars, and how that relates to the purely F=ma of the universe. Somehow a mechanism got introduced into the conversation, and complicated the issue. I just would like to know if there is enough energy released through fusion to accelerate the universe as we see it. Irrespective of the specific mechanism. Or is there just not enough energy to begin with?

 

[Drakkith]

Thanks for your reply Drakkith, it didn't seem right that radiation pressure could account for all energy released from stars. The basic reason for this post in the first place, is that I am curious about the amount of energy released from stars, and how that relates to the purely F=ma of the universe. Somehow a mechanism got introduced into the conversation, and complicated the issue. I just would like to know if there is enough energy released through fusion to accelerate the universe as we see it. Irrespective of the specific mechanism. Or is there just not enough energy to begin with?

Let me first say that I don't think the idea even fits with being possible, however assuming that it might be there simply isn't enough energy to do that. As I demonstrated in my previous posts the radiation pressure is simply much too weak. To even cause an actual acceleration the radiation pressure would need to overcome gravity, and it is not doing that.

 

[gregtomko]

radiation pressure is simply much too weak. To even cause an actual acceleration the radiation pressure would need to overcome gravity, and it is not doing that.

I understand that. It is fascinating to me that in this thread I have been bombarded by assumptions of mechanisms, and reasons why there is no correlation. I am not trying to draw a correlation, or propose a mechanism. I would just like to know about the quantities of energy involved. I really had no idea this was such a contentious question.

 

[gregtomko]

The reason I originally posted this question is, I would like to know if there is too little energy released from stars fusion, to through whatever mechanism, cause the acceleration of the expansion of the universe as we observe it. If there is a difference in the quantity of energy available, to energy needed, is there a known ratio? Or even any understanding of what the ratio might be?

 

[Drakkith]

I understand that. It is fascinating to me that in this thread I have been bombarded by assumptions of mechanisms, and reasons why there is no correlation. I am not trying to draw a correlation, or propose a mechanism. I would just like to know about the quantities of energy involved. I really had no idea this was such a contentious question.

Why would we not ask for mechanisms? The question is entirely unanswerable without taking a mechanism into account.

The reason I originally posted this question is I would like to know if there is too little energy released from stars fusion, to through whatever mechanism, cause the acceleration of the expansion of the universe as we observe it. If there is a difference, is there a known ratio?

To my knowledge no, there is not enough energy to do this through any mechanism. I don't believe there is a ratio because I don't believe there is even a mechanism that could cause the acceleration of the expansion from the release of energy by stars. Someone correct me if I'm wrong.

 

[PAllen]

The reason I originally posted this question is, I would like to know if there is too little energy released from stars fusion, to through whatever mechanism, cause the acceleration of the expansion of the universe as we observe it. If there is a difference in quantities of energy, is there a known ratio?

If you assume (a la Newton, in violation of GR) that you could have a static background space in which stars fuse, emit energy, acting altogether as a mixed gas of light, particles, and stars: then you would have decreasing rate of expansion not acceleration. All contributors to pressure of the gas would decrease as the universe expanded. Thus, this hypothesis is trivially counter-factual.

 

[gregtomko]

The question is entirely unanswerable without taking a mechanism into account.

Why is it that the acceleration of the expansion of the universe, related to the mass of the universe, can not be related to the energy necessary to cause it? Why does there have to be a mechanism? I know there HAS to be a mechanism to EXPLAIN it, but to just relate the ratio of energy in, to energy of acceleration, seems like a simple concept.

 

[gregtomko]

If you assume (a la Newton, in violation of GR) that you could have a static background space in which stars fuse, emit energy, acting altogether as a mixed gas of light, particles, and stars: then you would have decreasing rate of expansion not acceleration. All contributors to pressure of the gas would decrease as the universe expanded. Thus, this hypothesis is trivially counter-factual.

I would like to know what "this hypothesis" is. I am not proposing a hypothesis. I am just asking a simple question.

 

[phinds]

Why is it that the acceleration of the expansion of the universe, related to the mass of the universe, can not be related to the energy necessary to cause it? Why does there have to be a mechanism? I know there HAS to be a mechanism to EXPLAIN it, but to just relate the ratio of energy in, to energy of acceleration, seems like a simple concept.

Yeah, but it keeps coming back to the fact that without a mechanism the number is pointless. I think that folks on this board, when answering questions, natually assume that there is a POINT to the question. Searching for the value of a meaningless statistic doesn't fit the bill, and without a mechanism, your entire discussion is just a search for the value of a meaningless statistic.

 

[PAllen]

I would like to know what "this hypothesis" is. I am not proposing a hypothesis. I am just asking a simple question.

The hypothesis is that energy released by fusion from stars could account for accelerated expansion. It can't. If this was the mechanism of expansion, the prediction would be for decreased rate of expansion rather than accelerated expansion.

 

[gregtomko]

Yeah, but it keeps coming back to the fact that without a mechanism the number is pointless. I think that folks on this board, when answering questions, natually assume that there is a POINT to the question. Searching for the value of a meaningless statistic doesn't fit the bill, and without a mechanism, your entire discussion is just a search for the value of a meaningless statistic.

Seriously, the POINT of the question is what the ratio of energy is, that's the whole point. There is no other point. I am sure that the question might be meaningless. Does that mean I should not ask the question?

 

[gregtomko]

The hypothesis is that energy released by fusion from stars could account for accelerated expansion. It can't. If this was the mechanism of expansion, the prediction would be for decreased rate of expansion rather than accelerated expansion.

I am not arguing with the concept, I would just like to know where to look for the information. If the energy needed to accelerate the universe is somewhat understood, and the mass of the universe is similarly understood, and the total amount of energy released from stars through time is similarly understood, then the ratio of how much energy is available to that which is needed to explain what we see, should also be similarly understood. I am just asking what that ratio is.

 

[gregtomko]

Maybe a more clear set of questions would be helpful. Is there a range of estimates for the energy needed to cause the universe to expand as it is observed? Is there an estimate of the mass of the universe? Is there an estimate of the total energy released through fusion in the universe?

 

[Drakkith]

Seriously, the POINT of the question is what the ratio of energy is, that's the whole point. There is no other point. I am sure that the question might be meaningless. Does that mean I should not ask the question?

The ratio of energy released by stars to the energy required to do what? Accelerate the universe? How can I figure out the required energy eithout a mechanism to explain how to figure out this required energy?

 

[Drakkith]

Maybe a more clear set of questions would be helpful. Is there a range of estimates for the energy needed to cause the universe to expand as it is observed? Is there an estimate of the mass of the universe? Is there an estimate of the total energy released through fusion in the universe?

Hold on. Are you asking about the expansion itself, or the acceleration of the expansion?

 

[gregtomko]

I am asking about the energy needed to cause the acceleration of the expansion.

 

[Drakkith]

Hmm. Would there even need to be an expenditure of energy? Or just a force? It isn't that objects are getting pushed away from each other, gaining velocity in space, but that space is expanding in between them.

 

[gregtomko]

It isn't that objects are getting pushed away from each other, gaining velocity in space, but that space is expanding in between them.

What is the difference between objects gaining separation in space, and space expanding between objects?

 

[Drakkith]

What is the difference between objects gaining separation in space, and space expanding between objects?

For one, an object cannot exceed the speed of light as measured by traveling through local space. (Non-expanding space around massive objects) However, two galaxies can be receding from one another at a rate greater than the speed of light because neither are traveling through local space anywhere close to that speed. Instead space itself is expanding between them, carrying them apart.

 

[gregtomko]

two galaxies can be receding from one another at a rate greater than the speed of light.

I thought relativity excluded that possibility. Doesn't time skew as the rate of those galaxies separation increases?

 

[gregtomko]

How can I figure out the required energy without a mechanism to explain how to figure out this required energy?

Just the simple equation of F=ma. There is a mass of the universe. There is an acceleration of the universe. There can be an expected F on the universe. From that force, a quantity of energy needed to satisfy the F=ma relationship can be calculated.