# Expansion of the universe | Potential Effects on Energy / Matter

I have been thinking for the past couple months on how the expansion of the universe effects the matter and energy within it. Please read every line, skipping any part of this thread will lead to confusion. Hopefully someone can shed some light on this amazing new question of universal expansion

Before I jump into the discussion lets review a few aspects of universal expansion that are crucial for the following aspect;

The universe expands to our currently knowledge due to "Dark Energy".

Dark energy is referred to use a force, but it is important to keep in mind Dark Energy can not be measured and does not induce any forces on matter or energy.

It simply expands the universe, which will lead into my next point.

Two Objects at rest in imaginary universe with no forces separated by 1 million light years will expand from each other.

So the distance is increasing but the velocity (kinetic energy) is still 0.

This is one of the most important factors of expansion.

So no energy is being used, yet the distance is increasing (remember this).

Now for the second aspect of the concept.

We know that if you take two masses and separate them, gravitational potential energy is gained in proportion to the distance of the objects.

So as distance increases energy is gained, as those masses will accelerate towards each other due to a force we know as "Gravity".

This force is a relatively weak force, although when large masses are involved it can hold you in your seat literally.

So knowing those two aspects, lets take at this easy to visualize analogy I have made.

Imagine a universe with 2 planets separated by 1 light year.

These planets will accelerate towards each other until impact gaining velocity (kinetic energy) the whole time. This is something everyone knows, drop an apple on your head and you will feel the impulse caused by the kinetic energy.

Lets go back to the imaginary universe, this time there is one large planet and one baseball.

To move this baseball 1 meter off the ground it takes 1N of energy.

If we separate these two masses by transferring energy from a machine or for simplicity lets say you are on the planet and threw this ball extremely far 1 light year away.

The energy you transferred into the ball is not lost simply transferred to KE and then from there transferred slower and slower to gravitational potential between the two masses.

Keep in mind gravitational potential is energy that both masses share.

If you ignore expansion this ball in a vacuum will return with exactly the same energy that you originally induced on it, following the laws of conservation of energy.

This is where the expansion of the universe gets tricky.

As the ball is travelling away the space between the planet and the ball when the ball reaches its climax is now greater due to the expansion. This means on the way back, there is more distance and thus energy that the ball will have. The universe also expands on the way back.

The measure is 68Km/s per million light years per second. So it is a VERY noticeable distance.

This also makes sense of why objects further away have increased red shift.

As distance increases expansion rate relative to acceleration induced by gravity is just too great so the masses increase in distance even though they are increasing in velocity, but decreasing in acceleration.

This does not break the laws, as conservation of energy does not apply to GR.

Let me know what you think and please leave any questions below, I coded a software to simulate this and am currently processing the simulation. Hopefully this will be a key to our understanding of how the universe works.

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Update after thinking about expansion and gravity.

The distance between two masses at which expansion is greater than the velocity of the objects. They would expand.

If they are within this point they will contract.

Two objects outside of the "gravitational expansion radius" would accelerate towards each other slow and slower, but velocity would increase as distance does as well.

pervect
Staff Emeritus
You might try reading Sean Caroll's article on the issue of energy conservation in GR at http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/

It's a good article, I'll quote some of the highlights:

It’s clear that cosmologists have not done a very good job of spreading the word about something that’s been well-understood since at least the 1920′s: energy is not conserved in general relativity. (With caveats to be explained below.)

The point is pretty simple: back when you thought energy was conserved, there was a reason why you thought that, namely time-translation invariance. A fancy way of saying “the background on which particles and forces evolve, as well as the dynamical rules governing their motions, are fixed, not changing with time.” But in general relativity that’s simply no longer true. Einstein tells us that space and time are dynamical, and in particular that they can evolve with time. When the space through which particles move is changing, the total energy of those particles is not conserved.

Having said all that, it would be irresponsible of me not to mention that plenty of experts in cosmology or GR would not put it in these terms. We all agree on the science; there are just divergent views on what words to attach to the science.

The relevance of this is that while a lot of your points do make sense from a Newtonian background, they don't give an insight into the actual state of affairs in GR.

Is Energy Conserved in General Relativity?

In special cases, yes. In general — it depends on what you mean by "energy", and what you mean by "conserved".

1 person
You might try reading Sean Caroll's article on the issue of energy conservation in GR at http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/

It's a good article, I'll quote some of the highlights:

The relevance of this is that while a lot of your points do make sense from a Newtonian background, they don't give an insight into the actual state of affairs in GR.

Thanks for the resource, it seems this would support my concept. Perhaps this is an explanation for the "loss of energy conservation". What if these changes in energy is what induces the expansion.

The energy gained by expansion would be due to the loss of energy through space?

That seems to be the only way this energy could be transferred.

Thank you for the help by the way!

bcrowell
Staff Emeritus
Gold Member
The universe expands to our currently knowledge due to "Dark Energy".

This is not true.

Bump for more feedback.

pervect
Staff Emeritus
Bump for more feedback.

If you read a bit more carefully, you'll find that your references are saying dark energy cause the expansion of the universe to accelerate, while you are saying that the dark energy causes the expansion itself.

Cosmologies without dark energy may still have expansion. Without dark energy, the expansion rate always slows down (deaccelerates). This is covered in most introductory cosmology texts.

Depending on whether the universe is at (1), above(2), or below(3) the critical density, if there were no dark energy the expansion rate would in case 1) slow down towards zero, in case 2) recontract (so the expansion would reverse sign at some point), and in case 3) expand forever.

This is an example as to why it's wrong to say dark energy causes expansion - in this example we have no dark energy, but we still have expansion.

Sean Caroll has a pretty good explanation of why dark energy causes the expansion rate to accelerate that came up on google, http://www.preposterousuniverse.com...oes-dark-energy-make-the-universe-accelerate/ using Friedman's first equation.

If you read a bit more carefully, you'll find that your references are saying dark energy cause the expansion of the universe to accelerate, while you are saying that the dark energy causes the expansion itself.

Cosmologies without dark energy may still have expansion. Without dark energy, the expansion rate always slows down (deaccelerates). This is covered in most introductory cosmology texts.

Depending on whether the universe is at (1), above(2), or below(3) the critical density, if there were no dark energy the expansion rate would in case 1) slow down towards zero, in case 2) recontract (so the expansion would reverse sign at some point), and in case 3) expand forever.

This is an example as to why it's wrong to say dark energy causes expansion - in this example we have no dark energy, but we still have expansion.

Sean Caroll has a pretty good explanation of why dark energy causes the expansion rate to accelerate that came up on google, http://www.preposterousuniverse.com...oes-dark-energy-make-the-universe-accelerate/ using Friedman's first equation.

I see then this scenario is now even more valid as the are even greater underlying circumstances that cause expansion that we don't know about.

Thanks for the clarification.

More comments please, I want you guys to bash this theory as hard as you can, but with objective evidence only.

Don't bring your main stream emotions into this thread please, I have full respect for the standard model and believe it I am just wondering whether or not this could become a new change to the standard model.

Nugatory
Mentor
We've gone far over the line for acceptable personal speculation here.