# Hubble Constant: Force Acting on Hydrogen Atom Due to Expansion of Universe

• Dogya
In summary, the question discusses the possibility of expressing the force of the expansion of the universe on a hydrogen atom through the Hubble constant. However, this is difficult to solve and may require considering a scenario with only two particles without electromagnetic interaction. Ultimately, the expansion of the universe does not truly exert a force in the traditional sense.
Dogya
Thread moved from the technical forums to the schoolwork forums
TL;DR Summary: Express through the Hubble constant the force that acts on the hydrogen atom due to the expansion of the universe

We have a hydrogen atom, in a gravitationally bound system nothing interesting happens to it. Let's put it in an empty world with only an electron and a proton. There are several forces acting on it: gravitational forces, electromagnetic forces, and since we only have two bodies, the expansion of the universe should work. The question is how to express through the Hubble constant and calculate the force of this expansion.
As pointed out to me, to solve this problem, we need to consider the case where we have two particles without electromagnetic interaction, such as 2 neutrons.
As I understood the solution has to be sought from Friedman equations.
This is difficult for me as I am only in my 2nd year of university.

In an empty universe there is no expansion, and even in spacetimes where there is expansion it isn't a force anyway.

Is there some context to this question? It doesn't seem like a coherent scenario to me.

Ibix said:
In an empty universe there is no expansion, and even in spacetimes where there is expansion it isn't a force anyway.

Is there some context to this question? It doesn't seem like a coherent scenario to me.
I meant that apart from the proton and the electron there is nothing else around that affects them in any meaningful way. So there will be expansion. And force, in its usual sense, really does not exist, but as we know the expansion of the universe happens with acceleration and so we can translate it into "newtons", getting the force

So you've got an FLRW universe everywhere filled with uniform density neutral matter and a non-zero cosmological constant, plus one electron and one proton?

The answer is still zero. The only sensible way to measure the acceleration of either particle is to measure its proper acceleration, and this will depend on the EM field at its location and nothing else (ignoring drag from the medium). The value of the EM field will depend on the cosmological constant, although the effect will be utterly negligible. I don't think there's a meaningful way to break the EM field down into "what it would be without the cosmological constant" and "the extra bit", though.
Dogya said:
the expansion of the universe happens with acceleration
Not in the sense you seem to mean. The acceleration isn't the second derivative of position as needed for Newton's laws.

## What is the Hubble Constant?

The Hubble Constant is a measure of the rate at which the universe is expanding. It is typically expressed in units of kilometers per second per megaparsec (km/s/Mpc). This constant helps astronomers understand the scale and age of the universe.

## How does the Hubble Constant relate to the expansion of the universe?

The Hubble Constant quantifies the relationship between the distance of galaxies and their recessional velocity due to the expansion of the universe. According to Hubble's Law, the farther away a galaxy is, the faster it is moving away from us. This relationship is directly proportional and is described by the Hubble Constant.

## What force acts on a hydrogen atom due to the expansion of the universe?

The expansion of the universe exerts a very small force on individual hydrogen atoms. This force is extremely weak compared to the atomic and molecular forces that bind atoms together. Therefore, the expansion of the universe does not significantly affect the behavior of hydrogen atoms on small scales.

## Does the Hubble Constant affect the forces within atoms?

No, the Hubble Constant and the expansion of the universe do not affect the forces within atoms. The electromagnetic force that holds electrons in orbit around the nucleus of an atom is vastly stronger than the effects of cosmic expansion. The Hubble Constant primarily affects the large-scale structure of the universe, such as the distances between galaxies.

## Can the expansion of the universe be observed on atomic scales?

No, the expansion of the universe cannot be observed on atomic scales. The effect of cosmic expansion is only significant over vast distances, such as those between galaxies. On the scale of atoms and molecules, the forces that govern their interactions are far stronger than the influence of the universe's expansion.

• Advanced Physics Homework Help
Replies
22
Views
1K
• Astronomy and Astrophysics
Replies
6
Views
2K
• Introductory Physics Homework Help
Replies
39
Views
2K
• Other Physics Topics
Replies
4
Views
3K
• Astronomy and Astrophysics
Replies
13
Views
2K
• Cosmology
Replies
6
Views
1K
• Astronomy and Astrophysics
Replies
43
Views
6K
• Atomic and Condensed Matter
Replies
3
Views
2K
• Cosmology
Replies
13
Views
3K
• Cosmology
Replies
8
Views
2K