Resolve Universal Expansion: Can We Measure It in the Lab?

[Ich]

$\Lambda$ in GR be interpreted as an intrinsic expansion of the underlying space? In this case universal expansion is a local property of space.

It can be interpreted as repulsive gravity, an acceleration. It's rather the time derivative of expansion $\ddot a$ , which is velocity$\dot a$.

Two objects at rest relative to each other separated by a distance would tend separate further if no other force or curvature is present. A volume element would tend to increase three times faster.

Yep, but starting with dx/dt=0, if the objects are at rest. To get expansion, dx/dt=Hx, you have to set the objects in motion accordingly. Or wait some time, in a de Sitter universe things eventually become comoving at nozero H.

The existence of a cosmological constant or dark energy imply a fifth force of nature exists, we just don't know how it works yet.

It's gravity. We don't know it source, but the force itself seems to be gravity.

The definition of a gravitationally bound mass is when the gravity is stronger than this undetermined force.

...and strong enough to overcome motion. Yes.

At the solar system level this force is of the scale of the Pioneer anomoly, but this anomoly is a contraction not an expansion.

No, it's several OOM smaller than the anomaly. And don't forget that there's even more dark matter, which acts contracting. Still 5 OOM too small, IIRC.

The reason we don't see it is because the effect is so small. If this effect is so much smaller than gravity at our scales it is even less significant at the scale of particles.

There's another reason, as I said just before: in Galaxies, Dark Matter is much denser than Dark Energy. As you'd treat both effects as cosmological corrections to the gravity of ordinary matter, the net correction is positive (contracting).

Based on a DeSitter universe with the observed Hubble expansion the length of an object doubles every 2.8E17 seconds, or 8.8 billion years. An electron expanding at this rate would hardly blink at this effect.

I get 3e17 s, and almost 6e17 s if the ends of the object were at rest initially.
This is my point during the whole thread: if things aren't moving from the start, they won't follow the expansion. Even in de Sitter space, the difference is remarkable. Without Lambda, or with a sufficient DM density, objects at rest wouldn't start receding at all. They would accelerate towards each other.
That's one of the reasons why atoms don't expand.
The other is, as you said, that they can absorb this little Lambda easily.
I don't know if I mentioned it, but such a repulsive force doesn't let bound systems grow. Instead, they settle in a slightly larger stable configuration.

 

[utesfan100]

It's gravity. We don't know it source, but the force itself seems to be gravity.

For dark energy I agree completely. For dark energy and the cosmological constant responsible for the increasing expansion rate of the universe I am not so set. My point is, unti lwe can account for it in a testable way, we can't say whether it is an unaccounted for effect in a known force or a new force.

Maybe it is the negative gravity from all the negative energy gravitons floating through "empty space". I have yet to see a model of such a system. I think the lack of a good model for a graviton is a major obsicle.

I get 3e17 s, and almost 6e17 s if the ends of the object were at rest initially.
This is my point during the whole thread: if things aren't moving from the start, they won't follow the expansion. Even in de Sitter space, the difference is remarkable. Without Lambda, or with a sufficient DM density, objects at rest wouldn't start receding at all. They would accelerate towards each other.

let us take an observer in a DeSitter frame. Two objects comoving with this DeSitter frame double their distance in 3e17 seconds. Two objects whose distance is constant at a given point in time will double their distance in 6e17 seconds, twice as long. Essentially, their rate of separation needs to accelerate from rest.

At 3e17 the rest objects will be moving slower than their comoving objects, but will also be closer to the origin of the DeSitter space with a %velocity closer to their local region of DeSitter space than they originally had. Asymtotically they will approach the Hubble velocity.

... assuming a perfectly flat DeSitter space. I think they go next to the frictionless planes and massless springs in the physics lab. :)

 

[Ich]

My point is, unti lwe can account for it in a testable way, we can't say whether it is an unaccounted for effect in a known force or a new force.

Well, you're right in principle. But I'm not aware of any research that doesn't treat the effect as gravitational (which includes Lambda in my way of thinking).

... assuming a perfectly flat DeSitter space. I think they go next to the frictionless planes and massless springs in the physics lab. :)

Just visit a void and wait some 120 Gy there. Not much left then except DE.