<p>When we say the Universe is expanding, we really mean that space is expanding. The Universe could be infinite in size, but there continues to be more and more space between objects. Essentially, objects are moving away from each other because more and more space is being created between them.</p>

<p>In the early Universe, matter was much closer together than it is now; this density caused extreme temperatures and no hadronic matter could form. The first expansion is thought to have occurred because of how hot and energetic everything was, and spacetime itself was expanded in an event we call the Big Bang.</p>

<p>As objects spread out from each other during the inflationary epoch, the Universe began to cool down. Now, dark energy is the main culprit for its accelerating expansion.</p>

<p>To answer your question, yes, dark energy is making all particles move away from each other, although farther objects move away from each other at a faster rate. Why is that?</p>

<p>Well, the only thing holding all atoms, stars, planetary systems and galaxies together are the four fundamental interactions — the strong force, weak force, electromagnetic force, and gravity. In space, the main attracting interaction is gravity. As such, dark energy will cause farther objects (which are less affected by our gravity) to move away at a faster and faster rate.</p>

<p>Think of it like you are holding a dog with a leash, and the ground begins to spread out from below you. You and your dog are being moved away in opposite directions, but you both stay close together because of the strong leash.</p>

<p>Now, your mention of atoms being torn apart is actually the basis of the <a href="https://en.wikipedia.org/wiki/Big_Rip" rel="nofollow">Big Rip hypothesis</a>. It states that dark energy will become more and more abundant until even closeby objects separate from one another. First, galaxies will be disbanded as the stars move away from each other in all directions.</p>

<p>Much later, the gravity of planetary systems won't be enough to hold them together. Later still, planets and stars will be disbanded into their molecules. This will eventually continue as the amount of dark energy increases, until not even atoms can be held together by the electromagnetic force, and the subatomic particles will be moved apart.</p>

<p>By the time the expansion of the Universe exceeds lightspeed at the subatomic scale, no particle will ever be able to interact with one another. The Universe would dissolve into countless lonely particles that won't be able to do anything. Now, the Big Rip hypothesis is only one of the three most known fates of the Universe. Currently, the most accepted theory is the <a href="https://en.wikipedia.org/wiki/Heat_death_of_the_universe" rel="nofollow">heat death of the Universe</a>.</p>

CC BY-SA 3.0
2016-02-25T05:37:04.410Z
Expanding universes predate "dark energy"
Conrad Turner
CC BY-SA 3.0
2016-02-25T05:48:06.013Z
@ConradTurner At the time of the Big Bang, they do. Nowadays the Universe is expanding due to dark energy.
Sir Cumference
CC BY-SA 3.0
2016-02-25T09:53:03.153Z
You're right that DE makes space expand at a faster rate than previously, but I think your otherwise nice answer could be improved if you discussed how DE is not a necessary condition for expansion.
pela
CC BY-SA 3.0
2016-02-25T14:42:35.943Z
Other forces, such as gravity or electrical charge can overcome the general expansive force. Earth is **not** getting bigger via this mechanism.
Wayfaring Stranger
CC BY-SA 3.0
2016-02-25T21:26:22.630Z
@WayfaringStranger Really? Gravity clearly doesn't keep farther objects from drifting away from us. The amount of dark energy in the Universe is increasing and according to the hypothesis I mentioned, it will eventually overwhelm electromagnetism and gravity at any scale.
Sir Cumference
CC BY-SA 3.0
2016-02-25T21:40:16.390Z
@pela Added that.
Sir Cumference
CC BY-SA 3.0
2016-02-25T23:02:42.413Z
@SirCumference Gravity is enough to keep the local cluster bound now. Whether dark energy will ever get strong enough to disrupt that is still a matter of speculation. If so, the time frame is at least 22 billion years from now: https://en.wikipedia.org/wiki/Big_Rip
Wayfaring Stranger
CC BY-SA 3.0
2016-02-25T23:29:53.403Z
@WayfaringStranger I know all this. I specifically said that gravity is holding together relatively close objects. I delved into the hypothesis and explained it.
Sir Cumference
CC BY-SA 3.0
2016-02-25T04:08:08.483Z
2016-02-28T09:49:57.343Z
2016-02-28T09:49:57.343Z
Sir Cumference
<p>What exactly is meant when we say the universe is expanding? I understand stars and galaxies are getting farther and farther away from us, but are individual particles (atoms, molecules, anything found on Earth, etc.) drifting away from each other as well? If no, then why not? If yes, then shouldn't it, at some point, get to a point when particles can no longer bond with each other?</p>

<expansion>
What exactly is meant by "expanding universe"?
creative_name
# What exactly is meant by "expanding universe"?

(Asked by: username_0 on 2016-02-25)

What exactly is meant when we say the universe is expanding? I understand stars and galaxies are getting farther and farther away from us, but are individual particles (atoms, molecules, anything found on Earth, etc.) drifting away from each other as well? If no, then why not? If yes, then shouldn't it, at some point, get to a point when particles can no longer bond with each other?

**Tags:** expansion


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## 1 answers

### Answer by username_1 on 2016-02-25. Score: 4

When we say the Universe is expanding, we really mean that space is expanding. The Universe could be infinite in size, but there continues to be more and more space between objects. Essentially, objects are moving away from each other because more and more space is being created between them.

In the early Universe, matter was much closer together than it is now; this density caused extreme temperatures and no hadronic matter could form. The first expansion is thought to have occurred because of how hot and energetic everything was, and spacetime itself was expanded in an event we call the Big Bang.

As objects spread out from each other during the inflationary epoch, the Universe began to cool down. Now, dark energy is the main culprit for its accelerating expansion.

To answer your question, yes, dark energy is making all particles move away from each other, although farther objects move away from each other at a faster rate. Why is that?

Well, the only thing holding all atoms, stars, planetary systems and galaxies together are the four fundamental interactions — the strong force, weak force, electromagnetic force, and gravity. In space, the main attracting interaction is gravity. As such, dark energy will cause farther objects (which are less affected by our gravity) to move away at a faster and faster rate.

Think of it like you are holding a dog with a leash, and the ground begins to spread out from below you. You and your dog are being moved away in opposite directions, but you both stay close together because of the strong leash.

Now, your mention of atoms being torn apart is actually the basis of the [Big Rip hypothesis](https://en.wikipedia.org/wiki/Big_Rip). It states that dark energy will become more and more abundant until even closeby objects separate from one another. First, galaxies will be disbanded as the stars move away from each other in all directions.

Much later, the gravity of planetary systems won't be enough to hold them together. Later still, planets and stars will be disbanded into their molecules. This will eventually continue as the amount of dark energy increases, until not even atoms can be held together by the electromagnetic force, and the subatomic particles will be moved apart.

By the time the expansion of the Universe exceeds lightspeed at the subatomic scale, no particle will ever be able to interact with one another. The Universe would dissolve into countless lonely particles that won't be able to do anything. Now, the Big Rip hypothesis is only one of the three most known fates of the Universe. Currently, the most accepted theory is the [heat death of the Universe](https://en.wikipedia.org/wiki/Heat_death_of_the_universe).

> **Comments:**
> **username_2**: Expanding universes predate "dark energy"  
> **username_1**: @ConradTurner At the time of the Big Bang, they do. Nowadays the Universe is expanding due to dark energy.  
> **username_3**: You're right that DE makes space expand at a faster rate than previously, but I think your otherwise nice answer could be improved if you discussed how DE is not a necessary condition for expansion.  
> **username_4**: Other forces, such as gravity or electrical charge can overcome the general expansive force. Earth is **not** getting bigger via this mechanism.  
> **username_1**: @WayfaringStranger Really? Gravity clearly doesn't keep farther objects from drifting away from us. The amount of dark energy in the Universe is increasing and according to the hypothesis I mentioned, it will eventually overwhelm electromagnetism and gravity at any scale.  
> **username_1**: @username_3 Added that.  
> **username_4**: @SirCumference Gravity is enough to keep the local cluster bound now. Whether dark energy will ever get strong enough to disrupt that is still a matter of speculation. If so, the time frame is at least 22 billion years from now: https://en.wikipedia.org/wiki/Big_Rip  
> **username_1**: @WayfaringStranger I know all this. I specifically said that gravity is holding together relatively close objects. I delved into the hypothesis and explained it.  

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