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

[gregtomko]

Oh, ok, let me think about that for a while, THANKS!

 

[phinds]

So the stars which have traveled less distance from the singularity, are between the ones that have traveled farther. The ones nearer to the singularity would feel equal pressure from the farther ones. The ones which have traveled farther however have more pressure from the inner stars.

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

 

[DaveC426913]

So the stars which have traveled less distance from the singularity, are between the ones that have traveled farther. The ones nearer to the singularity would feel equal pressure from the farther ones. The ones which have traveled farther however have more pressure from the inner stars.

Yeah greg, you must disabuse yourself of this notion that any place in the universe is any closer for farther from the origin of the BB.

Take a deflated balloon, glue pennies all over its surface. Now inflate the balloon to the size of a beachball. Which balloon can lay claim to being closest to the origin, when the balloon was tiny? None of them. All of them.

Our 3D universe is equivalent to the 2D surface of this balloon. The surface of the balloon has no centre. All points are equally (that is to say, not) privileged.

 

[dacruick]

Yeah greg, you must disabuse yourself of this notion that anyplace is the universe is any closer for farther from the origin of the BB.

Take a deflated balloon, glue pennies all over it. Now inflate the balloon to the size of a beachball. Which balloon can lay claim to being closest to the origin, when the balloon was tiny? None of them. All of them.

So there is no centre of the universe?

 

[DaveC426913]

So there is no centre of the universe?

Correct. Or more accurately, everywhere is the centre.

 

[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?