Dark Energy & Expansion of Spacetime

In summary: For now, I'll just say that physicists tend to emphasize how tiny is the force of gravity compared to the other forces (i.e. strong nuclear force) but nobody seems to have a word of how even tinier the force of dark energy is - why is that?That's a really good question! It's not completely clear to me why the force of gravity is so tiny, either. It might have something to do with the way the universe is designed. Or it might have something to do with the way the laws of physics work. I'm not sure.Does it mean that "empty space" is acted upon by dark energy but when (dark) matter is present it tells space how to curve and also
  • #1
member 563992
PLEASE BE ADVISED: I'm a complete ignorant with regards to the details of what I'm about to say and I've never looked at the mathematics of the subject, let alone understand it. So most of what I am about to say comes from pop science. Excuse me in advance if I sound stupid or rhetorical.

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My question: how is space being accelerated in it's expansion? I think:

1. It happens everywhere (inside galaxies etc.)
2. However, within galaxies, G > than the force of dark energy thus we don't see it
3. It must act on the whole scale of the universe where it becomes visible between galaxies (that's how we measured it -- as per supernova's)
4. Therefore I've some discomfort with this situation, namely:

a) How come is the force of gravity bigger than dark energy at those scales? How do we explain it? What model do we use and what data? Is there any link between dark matter and dark energy? Could dark matter override dark energy in galaxies/galaxy clusters?
Physicists tend to emphasize how tiny is the force of gravity compared to the other forces (i.e. strong nuclear force) but nobody seems to have a word of how even tinier the force of dark energy is - why is that?

b) Does it mean that "empty space" is acted upon by dark energy but when (dark) matter is present it tells space how to curve and also how to expand or how to avoid expanding in that region/area? Would this even make sense? Probably not: it would just overcome the force as we see it in atoms: we don't see gravity effect on such scale (i.e. weak nuclear force is much much bigger than gravity yet we don't disregard gravity, we simply state it's insignificant at that scale, but at larger scales obviously, gravity does play a role we can observe -- so it's scales between dark gravity <-> dark energy? or could there be a relationship in terms of interacting fields?).

c) How can this play into our model of quantum gravity (for further explorations) and just ordinary current models?

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[Moderator's note: second part moved to separate thread.]
 
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  • #2
ToddM4 said:
I'm a complete ignorant with regards to the details of what I'm about to say and I've never looked at the mathematics of the subject, let alone understand it. So most of what I am about to say comes from pop science.

This should be a red flag that you should take a look at a source that is not pop science. You can't learn actual science from pop science sources.

ToddM4 said:
how is space being accelerated in it's expansion

Do you mean just the expansion itself, or the effects of dark energy? They're not the same thing.

The expansion itself exerts no "force" at all; it's just inertia. Things are moving apart and inertia keeps them moving apart.

Dark energy does exert a "force", in the sense that if you pick any two free-floating objects in a spacetime with dark energy, the dark energy will cause them to accelerate away from each other. But the magnitude of the acceleration varies with the distance between the two objects. That's why the effects of dark energy are completely negligible on scales such as our solar system or our galaxy or even clusters of galaxies. You have to get up to separations of hundreds of millions to billions of light-years before the acceleration caused by dark energy becomes significant.

ToddM4 said:
"empty space"

Notice that I said all that above without once using the term "space" (much less "empty space"). "Space" is not something physical; it's an artifact of how you choose your coordinates. Spacetime is the physical thing. The "acceleration" caused by dark energy can be thought of as an effect of the way dark energy curves spacetime.

ToddM4 said:
More of my confusion

This belongs in a separate thread, and will be moved to one shortly.
 

1. What is dark energy?

Dark energy is a hypothetical form of energy that is thought to make up about 70% of the total energy in the universe. It is believed to be responsible for the accelerating expansion of the universe.

2. How is dark energy related to the expansion of spacetime?

Dark energy is thought to be the driving force behind the expansion of spacetime. It is believed to be a property of the fabric of space itself, causing it to expand at an accelerating rate.

3. Can dark energy be detected?

Currently, there is no direct way to detect dark energy. It does not emit any light or radiation that can be observed, and its effects can only be seen through its influence on the expansion of the universe.

4. Is dark energy the same as dark matter?

No, dark energy and dark matter are two different concepts. Dark matter is a type of matter that does not emit light or interact with electromagnetic radiation, but it is thought to make up about 27% of the total energy in the universe.

5. How does the study of dark energy and the expansion of spacetime impact our understanding of the universe?

The study of dark energy and the expansion of spacetime is crucial for understanding the past, present, and future of the universe. It can help us understand the overall structure and evolution of the universe, as well as the role of dark energy in shaping its fate.

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