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

[dacruick]

Correct. Or more accurately, everywhere is the centre.

In your balloon analogy, is the distance between the centre of the balloon and any point on the surface represented in our universe as time?

 

[gregtomko]

There is no "nearer to the singularity". There is no center. The singularity happened EVERYWHERE.

Ok, but if there only ended up being 3 stars, just for simplicities sake, and they happened to be oriented in a line, with one in the middle and the others on either side. Then wouldn't the one in the middle have equal energy pushing on it, and the ones on either end have energy only pushing from one side?

 

[dacruick]

Ok, but if there only ended up being 3 stars, just for simplicities sake, and they happened to be oriented in a line, with one in the middle and the others on either side. Then wouldn't the one in the middle have equal energy pushing on it, and the ones on either end have energy only pushing from one side?

pending my last post being correct, that would mean that they are both being "pushed by energy" in the same direction of time. So I would have to say that the idea of being "pushed by energy" here is misleading.

 

[DaveC426913]

In your balloon analogy, is the distance between the centre of the balloon and any point on the surface represented in our universe as time?

Remember, it is an analogy, and does break down if you "stretch" it too far. You could look at the expansion of the balloon as the dimension of time.

It was very small. Now it's big. Eventually it will get so large as to burst and scare the baby, making your mom yell at you and send you outside.

 

[gregtomko]

Either way, wouldn't all those photons pushing all the particles apart help to expand the "balloon?"

 

[DaveC426913]

Either way, wouldn't all those photons pushing all the particles apart help to expand the "balloon"?

Yes, that is the flaw in your argument. The question no one has answered yet is 'why is this otherwise plausible mechanism not so'? 'Why does photon pressure not push stars apart'?

 

[phinds]

Either way, wouldn't all those photons pushing all the particles apart help to expand the "balloon"?

gregtomko, we have tried 6 ways from Sunday to help you understand that your idea just doesn't work. I think at this point it would make sense for you to find some reliable sources and read up on the whole thing. This will not only make you forget about your current line of thought, it will also teach you a bunch. This spotty explanation by semi-random questions that were're giving you here is not the best way to go about this.

 

[gregtomko]

Ok, sounds good to me. Thanks for your time though, I really appreciate it!

 

[DaveC426913]

gregtomko, we have tried 6 ways from Sunday to help you understand that your idea just doesn't work.

At the risk of being pedantic, all we've really done is explain why we have better ideas. We have not actually shown how his hypothesis is wrong.

I have too many beers in me to create an answer right now, but I think you deserve one.

 

[phinds]

At the risk of being pedantic, all we've really done is explain why we have better ideas. We have not actually shown how his hypothesis is wrong..

OK, I'll bite ... where did I go wrong with the "same pressure from all directions ==> no movement" explanation?

 

[gregtomko]

I hope it has to do with the balloon example, because I don't understand how pressure between all the particles on the "balloon" wouldn't have the result of pushing them all farther apart from each other. Even when you add the third dimension, that too being contiguous with itself and the other dimensions, I don't see what difference it makes.

If I figure that one out, and how Bell's theorem works, I will happy. :-)

 

[DaveC426913]

OK, I'll bite ... where did I go wrong with the "same pressure from all directions ==> no movement" explanation?

Not sure...

 

[phinds]

Not sure...

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

 

[gregtomko]

What I am missing is why equal pressure from all directions does not translate to equal expansion in all directions.

 

[DaveC426913]

Got it:

One of the ways we know that this pressure does not explain expansion is this:

If this pressure from stars were the right idea, then pressure (and thus expansion) would be greatest between objects in close proximity and lesser between objects of greater separation. Two stars one hundred light years apart would push each other with greater force than two stars one hundred thousand light years apart. Two stars a mere one light year apart would push dramatically stronger yet.

But that is not what we observe. What we observe is exactly the opposite. Objects that are farther apart are accelerating away from each other the fastest, whereas objects in close proximity are accelerating away slower. Furthermore, objects even closer than this (scales less than galaxies) are not accelerating away from each other at all.

The proposed mechanism does not explain what we actually observe.

 

[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.