[Claes Gauffin]

Claes Gauffin  asked the Naked Scientists:
   
On the accelerating expansion of the universe.

We have learned that not only is the universe expanding, it is doing so at an increasing speed, i.e. every object in the universe is accelerating.

School physics teaches that an accelerating body gains kinetic energy. And mustn't this energy be supplied continuously?

Now, if the first law of thermodynamics holds, who or what is supplying this energy? And how is it constantly transferred to all these increasingly energetic bodies? Is this where "dark energy" crops up as a supporting crutch for a theory that is getting a bit long in the tooth?

Best wishes,
Claes

What do you think?

[Kryptid]

The short answer is: nobody knows.

Something else that needs to be pointed out is that the expansion of the Universe does not transfer kinetic energy to celestial bodies. From each bodys reference frame, they are sitting still and space is expanding equally in all directions around them. It doesn't cause them to move.

[yor_on]

Tell me, do you think there is gravity existent in the expansion? If you think there is, does it come 'instantly' or does it 'propagate'. Can there be a defined 'space', measurable, without gravity? What would such a 'space' look like?

One-dimensional maybe?

So, would you be able to measure it?

If now gravity is what defines a 'space' and it 'propagates' it 'propagates in something you can't measure. Alternatively 'gravity' becomes 'instantly' in those new 'expansions'. In the first cause 'gravity' is a 'force' of some kind propagating in a unmeasurable 'medium'. But if it was so and space 'expanded' the gravity should 'weaken' with the distances growing. And so also possibly be expected to 'dilute' everywhere, as we might define it as of being of one 'quantity' inside SpaceTime, coupled to the definition of mass we use.

If it then comes 'instantly' we find that 'space' and 'gravity' is one and the same, then the question becomes from where that 'gravity' comes. In Einsteins definitions SpaceTime is a whole. The observer is what defines both 'distances' and 'time'. My definition won't be yours, but both will be as valid, as measured from our own frame of reference. So, if distance is a questionable thing, maybe that is what we should look at.

Then you have the possibility of us all 'shrinking' too, that would create the same impression. I'm not sure the 'room' needs more 'energy'  to expand, but I'm pretty sure it needs 'gravity' to exist.
==

There is one definition more you might use, or add, if we assume that gravity is coupled to energy, or possibly equal to 'energy' in some way. Then the rooms expansion might be a result of more gravity, or if you like, the quantity of gravity raising is a result of the rooms expansion which is a pretty tricky one as it involves something growing as it 'produce' more 'gravity'. That one comes directly from the idea of a 'whole SpaceTime' where nothing ever gets lost, just transforms. So the 'energy' to expand could then be defined as coming from SpaceTime itself. It opens for the question of what 'energy' really is naturally. Myself I wonder about what 'distance' is

[MikeS]

If space is being created to make the universe expand then presumably gravitational potential energy is being created.  Where's that come from then?  []

[Phractality]

I know the answer, but it's not mainstream science. If I tell you, I'll be censored. Try asking in New Theories.

[Nizzle]

If space is being created to make the universe expand then presumably gravitational potential energy is being created.  Where's that come from then?  []

It has always been there, it only reduces in density cause it's stretched out more

[MikeS]

If space is being created to make the universe expand then presumably gravitational potential energy is being created.  Where's that come from then?  []

It has always been there, it only reduces in density cause it's stretched out more

But shouldn't it increase with distance?

[imatfaal]

It tends towards zero from negative with increased distance; which is an increase in a way.  I think the balancing out is  some form of contribution from the vacuum energy - but my mind is frazzled by the unseasonal heat in London and cannot think straight

[MikeS]

imatfaal

If GPE is a contribution from the vacuum energy and space is being created then vacuum energy is being created but this would seem to contravene the first law of thermodynamics?

[imatfaal]

Mike - my mind was frazzled by heat yesterday, and today it is alcohol and heat; you have to bear in mind signs.

U is negative U= -GMm/r^2 but so is vacuum energy.  A movement from low r to high r makes gpe decrease toward zero from negative (which in abs terms is an increase) but also makes more negative zpe energy.  An increase in negative zpe is balanced by a decrease in negative gpe.  I hope that makes sense


edit

and if it does, after two pints and a bottle of chablis and one of sancerre I will be very happy

[MikeS]

imatfaal

I have just returned home after five hours on the beer and spirits and it makes perfect sense.
However, tomorrow is another day.

[MikeS]

Quote
"What provides the energy for the universe to expand?
We have learned that not only is the universe expanding, it is doing so at an increasing speed, i.e. every object in the universe is accelerating."

The mainstream answer would seem to be dark energy / the gravitational constant. 
Could it not be something far simpler like photons (and possibly neutrinos)?  Photons carry energy to 'push'.  Not a lot admittedly but there are an awful lot of them, they are everywhere and they are being continuously produced.

[JP]

The mainstream answer would seem to be dark energy / the gravitational constant. 
Could it not be something far simpler like photons (and possibly neutrinos)?  Photons carry energy to 'push'.  Not a lot admittedly but there are an awful lot of them, they are everywhere and they are being continuously produced.

The problem is that whatever is going on is an anomaly.  Nothing we can detect via electromagnetic/weak foces explains these effects when paired with models we know are accurate over smaller scales.  So either it's something we can't detect, or the models need to be fixed.  Scientists are working on both options.

The reason it can't be just photons or neutrinos is that we can detect them both through electromagnetic/weak interactions.  Neutrinos may play a role, since they are very hard to detect, but if they were present in numbers that would explain all these anomalies, we'd know about it.  A culprit might be something that's even harder to detect than neutrinos, in which case it could be out there and we just haven't seen it yet.

[yor_on]

Heh another proof of how human 'mind lubrication' can work wonders.
Single malt has a low_ely viscosity.
=

And taste.