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

[gregtomko]

OK! That puts it to rest... for now... Thanks again!

 

[DaveC426913]

Guess I asked that one badly. What I mean is, why is that not a good explanation? What is incorrect about it?

I guess my difficulty was that relies on some assumptions about the shape of our universe, which we know little about. We'd have to accept them as true first before your argument is granted.

Doesn't feel right trying to debunk something that's concrete and right in front of us, by invoking something so speculative and distant.

 

[yoron]

Ahh, but then we have all those virtual particles too :)

I think they lay in wait, and as they realize that they are in a SpaceTime with planets they pop up to 'push', our typical party pranksters. To get around the question of why they shouldn't push 'evenly' I will now suggest that they 'push' on 'space'. To get around those now arguing that 'space' therefore is a aether, ahh, I will now suggest that they 'push' on 'gravity'..

So there, a perfectly reasonable explanation, covering ahh, a lot.

No I'm not serious, but I've been waiting on someone using 'virtual particles' for the longest time :)

 

[gregtomko]

where did I go wrong with the "same pressure from all directions ==> no movement" explanation?

Could someone explain the rational behind, "same pressure from all directions ==> no movement"? It seems counter intuitive to me. Specifically why wouldn't equal pressure in all directions translate into equal expansion in all directions. Doesn't the idea that the universe may someday have a "big crunch" rely on gravity, a force pulling all objects together? How is that contraction possible, but the opposite expansion not?

 

[juanrga]

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?

No. In fact the mass M of the Universe is constant.

 

[gregtomko]

that is very interesting, where does the mass go if photons are massless?

 

[gregtomko]

oh, OK, they don't have "rest" mass, but they aren't at rest. I wasn't aware they had mass when traveling.

 

[juanrga]

oh, OK, they don't have "rest" mass, but they aren't at rest. I wasn't aware they had mass when traveling.

Rest mass m is a confusing name. It is not the mass of an object when it is only at rest. Rest mass is the mass of the object with independence of its motion and in modern literature it is best named invariant mass or just mass. When the object is moving its mass m is the same than if was at rest. m=0 for a photon always.

 

[Drakkith]

oh, OK, they don't have "rest" mass, but they aren't at rest. I wasn't aware they had mass when traveling.

They do not have mass, ever. They have momentum and energy. Both mass and energy contribute to gravity. There is a confusing thing called "relativistic mass" that shouldn't have ever been called mass to begin with. When you think of mass only think of "rest mass" or "invariant mass". Both are the same thing. When a star emits light it does lose a small amount of mass thanks to the missing energy that the photon took. While in transit that photon is affecting the space around it through gravity. Once the photon is absorbed the energy it carried is turned back into mass, making whatever absorbed it slightly more massive.

 

[gregtomko]

They do not have mass, ever. They have momentum and energy. Both mass and energy contribute to gravity. There is a confusing thing called "relativistic mass" that shouldn't have ever been called mass to begin with. When you think of mass only think of "rest mass" or "invariant mass". Both are the same thing. When a star emits light it does lose a small amount of mass thanks to the missing energy that the photon took. While in transit that photon is affecting the space around it through gravity. Once the photon is absorbed the energy it carried is turned back into mass, making whatever absorbed it slightly more massive.

That is exactly the way I thought it worked. How does that relate to the earlier post

No. In fact the mass M of the Universe is constant.

If the mass is no longer in the star while the photons are in transit, how can the mass of the universe stay constant? Or maybe that was referring to the relativistic mass of the universe?

 

[Drakkith]

That is exactly the way I thought it worked. How does that relate to the earlier post

If the mass is no longer in the star while the photons are in transit, how can the mass of the universe stay constant? Or maybe that was referring to the relativistic mass of the universe?

When talking about dark energy and expansion and all that, both energy and mass have the same effect. So turning the mass into energy does nothing to the universe as a whole. Everything is still conserved.

Edit: I think that radiation pressure DOES happen to everything. The Sun is pushing objects away from it all the time. However the force of this pressure is extremely small and it also falls off exponentially with range. So while it probably does contribute to a very very slight "expansion", it is many orders of magnitude too small to cause the effect we see on a universal scale. See the table here: http://en.wikipedia.org/wiki/Radiation_pressure#In_interplanetary_space
Notice that at a distance of 1 AU the pressure is 100 times LESS than it is at 0.1 AU from the Sun. For 4 light years the amount of pressure is 63,990,987,667.36 times LESS than it is at 1 AU. So the nearest star experiences 64 billion times less radiation pressure from the Sun than the Earth does. (Pressure falls off at the square of the distance from the emitting object. 4 Lightyears = 252,964.4 AU. 252,964.4^2 = 63,990,987,667.36)

Edit 2: For a star at the other end of our galaxy, 100,000 ly away, assuming the light could even reach it without being absorbed first, which it cant, the pressure would be 39,994,367,292,100,000,000 times less. (That's almost 40 quintillion times less. About 40 billion billion times less)
I really hope all my math is correct lol.

 

[gregtomko]

What I am questioning is if the total quantity of energy released through nuclear fusion throughout the history of the universe is enough to equal the acceleration we observe. Not if we see certain effects on certain systems. As a whole, the proportion between how much energy is necessary to accelerate the universe as we see, and the amount of energy released in stars throughout time... is that a known ratio?

 

[phinds]

What I am questioning is if the total quantity of energy released through nuclear fusion throughout the history of the universe is enough to equal the acceleration we observe. Not if we see certain effects on certain systems. As a whole, the proportion between how much energy is necessary to accelerate the universe as we see, and the amount of energy released in stars throughout time, is that a known ratio?

I have no idea what the quantitative answer to your question is, but I doubt it matters because you have to have a plausible mechanism for transferring the energy released in the middle of stars to points MANY light years away, and there isn't any.

 

[gregtomko]

you have to have a plausible mechanism for transferring the energy released in the middle of stars to points MANY light years away, and there isn't any.

I only ask the question because I am not an astrophysicist. I am not asking about the mechanism, just about the relationship in energy.

 

[phinds]

I only ask the question because I am not an astrophysicist. I am not asking about the mechanism, just about the relationship in energy.

Well, to be fair, you were NOT asking "JUST" about the relationship, you said

What I am questioning is if the total quantity of energy released through nuclear fusion throughout the history of the universe is enough to equal the acceleration we observe

so your full question does bring up the need for a mechanism since otherwise equating the two is not in any way meaningful.

Now, don't get me wrong, I DO get (now that you've mentioned it twice ... I'm a little slow sometimes) that you are NOT asking about a mechanism, but do you see my point that your question as asked really does bring in a mechanism, else is somewhat meaningless?

 

[gregtomko]

It seems to me that the question of meaningless or meaningful, rests on the relationship of the quantities of energy involved.

 

[gregtomko]

I am just curious, is this an understood proportion?

 

[phinds]

It seems to me that the question of meaningless or meaningful, rests on the relationship of the quantities of energy involved.

But that's my point ... there IS NO realationship. I mean, comparing numerical quanties doesn't have any meaning unless the quantities describe things that are somehow related.

You might as well add up all the fuel costs for all ocean going vessels this year and compare it to all the fuel costs for automobiles for this year. What does that comparison tell you? Nothing meaningful about the realtionship between ships and cars.

 

[phinds]

I am just curious if this is an understood proportion?

That's a reasonable question and I don't know the answer, but once you HAVE the answer, what do you DO with it? I just can't get how it MEANS anything.

EDIT: I think I'm coming across as being hard to get along with in this. I don't mean to be. What I SHOULD be doing is ASKING, what do you think it will TELL you if/when you get a quantitative answer?

 

[gregtomko]

I am not sure where I am going with it either, it just seems like there might be some significance if there was a similarity. It would at least be a way to disprove an intuitive, yet overly simplistic connection, if there were no similarity.

 

[phinds]

I am not sure where I am going with it either, it just seems like there might be some significance if there was a similarity. It would at least be a way to disprove an intuitive, yet overly simplistic connection.

I see what you are saying, but even if the quantities were exactly the same, it would have no significance because of the lack of a mechanism relating the two. They just really don't have anything to do with each other.

 

[Drakkith]

What I am questioning is if the total quantity of energy released through nuclear fusion throughout the history of the universe is enough to equal the acceleration we observe. Not if we see certain effects on certain systems. As a whole, the proportion between how much energy is necessary to accelerate the universe as we see, and the amount of energy released in stars throughout time... is that a known ratio?

It is not. It isn't even close.

 

[gregtomko]

It is not. It isn't even close.

Which way is it not close, and where can I find information on that?

 

[gregtomko]

phinds, I don't want to sound sarcastic, but if the two quantities just happened to be the same, you don't think there would be some significance?

 

[phinds]

phinds, I don't want to sound sarcastic, but if the two quantities just happened to be the same, you don't think there would be some significance?

No more than I would find it significant that the total amount of fuel costs for all ocean going vessels this year was the exact same amount as the total fuel costs for all the cars this year. They just don't have anything to do with each other.

 

[gregtomko]

If the whole business of dark energy is so unknown, how can you be sure of that? I would think that conservation of energy in the universe, is far more unified than the international market price for fuel.

 

[Drakkith]

Which way is it not close, and where can I find information on that?

It's not nearly enough. The Earth experiences around 5.823 x 10^8 Newtons of radiation pressure. The force of gravity from the Sun is about 3.5222 x 10^22 Newtons. That means that the radiation pressure reduces the net force on Earth to 35,221,999,999,999,417,700,000 Newtons. (Round it off and its 3.5222x10^22)

 

[phinds]

If the whole business of dark energy is so unknown, how can you be sure of that? I would think that conservation of energy in the universe, is far more unified than the international market price for fuel.

Well, you have to imagine a mechanism whereby the use of energy in stars has an effect that is STRONGER the farther away you are from the star. I just don't buy it. I stand by my statement but I'll grant you that I don't KNOW that it isn't happening. I'd be willing to be lots of money against it though, and I'm not a betting man.

 

[gregtomko]

It's not nearly enough. The Earth experiences around 5.823 x 10^8 Newtons of radiation pressure. The force of gravity from the Sun is about 3.5222 x 10^22 Newtons. That means that the radiation pressure reduces the net force on Earth to 35,221,999,999,999,417,700,000 Newtons. (Round it off and its 3.5222x10^22)

I am not talking about the instantaneous acceleration on our solar system. The question is about the total energy released throughout time by starts in the universe, related to the total acceleration we see in the universe as a whole.

 

[gregtomko]

you have to imagine a mechanism whereby the use of energy in stars has an effect that is STRONGER the farther away you are from the star

That seems to be the similarity between dark energy and dark matter, they are stronger than they should be, the farther away you get. That was the inspiration for the question.

 

[Drakkith]

I am not talking about the instantaneous acceleration on our solar system. The question is about the total energy released throughout time by starts in the universe, related to the total acceleration we see in the universe as a whole.

Extrapolating that out, since radiation pressure is mainly produced by stars, and stars only make up about 1.5% of all matter and dark matter (the stuff that generates gravity), then we can see that the contribution of radiation pressure is absolutely miniscule compared with the combined gravity of the universe. (As my post above showed we can think of radiation pressure as a reduction in gravitation force)

That seems to be the similarity between dark energy and dark matter, they are stronger than they should be, the farther away you get. That was the inspiration for the question.

We have no idea what to expect from either dark matter or dark energy.
Also, what about them is stronger?

 

[gregtomko]

Extrapolating that out, since radiation pressure is mainly produced by stars, and stars only make up about 1.5% of all matter and dark matter (the stuff that generates gravity), then we can see that the contribution of radiation pressure is absolutely miniscule compared with the combined gravity of the universe.

That would be quite informative if the whole concept of dark matter was at all understood.

We have no idea what to expect from either dark matter or dark energy.
Also, what about them is stronger?

I thought that's what I was saying. That dark energy is needed to explain the extra acceleration of the universe the farther away we look. That dark matter is needed to explain the gravitational pull to hold stars farther away from the center of galaxies. The farther away, the stronger the "dark" forces appear to be.

 

[phinds]

That seems to be the similarity between dark energy and dark matter, they are stronger than they should be, the farther away you get. That was the inspiration for the question.

True for dark energy, not dark matter. Yeah, I get the connection, but I still don't believe there's the correlation that you are looking for.

EDIT: I should add --- I learned some time ago that the universe really doesn't give a rat's *** WHAT I believe.

 

[Drakkith]

That would be quite informative if the whole concept of dark matter was at all understood.

OR you could admit that radiation pressure is not a likely possibility to explain universal expansion. That seems much more reasonable than one liners aimed at someone's post you simply don't like. In the future try to understand the subject more before shooting down someone who has actually done the math.

I thought that's what I was saying. That dark energy is needed to explain the extra acceleration of the universe the farther away we look. That dark matter is needed to explain the gravitational pull to hold stars farther away from the center of galaxies. The farther away, the stronger the "dark" forces appear to be.

Dark matter is spread throughout the galaxy, not concentrated in the center. It's effects don't get stronger with increasing distance. Dark energy does not either. The [STRIKE]acceleration[/STRIKE] rate of expansion increases with distance because the space in between galaxies is expanding all at the same rate. IE if you break space down into chunks you will find that each piece is expanding at the same rate. Hence the reason the expansion is faster at increasing distances is because you have more pieces of space expanding between us.

Edit: The expansion is accelerating because of dark energy.

 

[gregtomko]

OR you could admit that radiation pressure is not a likely possibility to explain universal expansion. That seems much more reasonable than one liners aimed at someone's post you simply don't like. In the future try to understand the subject more before shooting down someone who has actually done the math.Dark matter is spread throughout the galaxy, not concentrated in the center. It's effects don't get stronger with increasing distance. Dark energy does not either. The acceleration increases with distance because the space in between galaxies is expanding all at the same rate. IE if you break space down into chunks you will find that each piece is expanding at the same rate. Hence the reason the expansion is faster at increasing distances is because you have more pieces of space expanding between us.

I specifically said I didn't know if radiation pressure is the mechanism. In reference to dark matter, I was saying that it appears to be more influential the farther from the centers of galaxies. Isn't that the whole concept, that galaxies rotations look odd because the outer stars rotate faster than they should? This is true or they wouldn't need to call it "dark matter" right? Just as "dark energy" is more influential on objects farther away from us. If it was a simple relationship there would be no question. Earlier in this line of posts it was stated that the reason the energy of fusion couldn't explain the acceleration of the universe, was somehow it did not fit the characteristics of the observed expansion. I am asking what is the observed relationship. I don't Know what the connection is, that's why I am asking.

 

[Drakkith]

I specifically said I didn't know if radiation pressure is the mechanism. In reference to dark matter, I was saying that it appears to be more influential the farther from the centers of galaxies. Isn't that the whole concept, that galaxies rotations look odd because the outer stars rotate faster than they should?

That is only one observed effect of dark matter. Gravitational lensing is another one. Saying the "dark forces" appear stronger further out implies that the actual force of gravity or expansion increases as distance increases.

This is true or they wouldn't need to call it "dark matter" right? Just as "dark energy" is more influential on objects farther away from us. If it was a simple relationship there would be no question. Earlier in this line of posts it was stated that the reason the energy of fusion couldn't explain the acceleration of the universe, was somehow it did not fit the characteristics of the observed expansion. I am asking what is the observed relationship. I don't Know what the connection is, that's why I am asking.

For every million parsecs of distance from the observer, the rate of expansion increases by about 74 kilometers per second. One parsec = 3.26 light years. Is that what you wanted?

 

[gregtomko]

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

That is your own conclusion, I am not sure that is the relationship.

For every million parsecs of distance from the observer, the rate of expansion increases by about 74 kilometers per second. One parsec = 3.26 light years. Is that what you wanted?

I am looking more specifically for the ratio of the amount of energy needed to accelerate the mass of the universe as we see it, compared to the amount of energy released through nuclear fusion in the stars of the universe throughout its expansion.

 

[Drakkith]

That is your own conclusion, I am not sure that is the relationship.

What? What relationship?

I am looking more specifically for the ratio of the amount of energy needed to accelerate the mass of the universe as we see it, compared to the amount of energy released through nuclear fusion in the stars of the universe throughout its expansion.

The energy needed to accelerate entire galaxies to a significant fraction of the speed of light? To throw out a guess I'd say more energy than has ever been output by every star in every galaxy combined.

 

[gregtomko]

That is exactly what I am interested in. I am sure there is a better understanding than a guess. I don't doubt you are correct about the ratio.

 

[gregtomko]

What? What relationship?

"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.

 

[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?