<p>There can be no such thing as &quot;empty&quot; space. Particles and anti-particles can and do pop into and out of existence on timescales that are shorter than <span class="math-container">$\sim \hbar/\Delta E$</span>, where <span class="math-container">$\Delta E$</span> is the total energy (including rest mass) of the created particle/anti-particle pair.</p>
<p>Thus your thought experiment is impossible.</p>

CC BY-SA 4.0
2023-12-28T18:28:17.087Z
The OP would obviously imply that these are removed as well. Otherwise space could not be called empty. It is only a hypothetical thought experiment after all, so you can imagine them being removed as well (some people actually think these vacuum fluctuations are tied in to matter)
Thomas
CC BY-SA 4.0
2023-12-29T15:51:07.387Z
Do this particles span the volume? There wouldn't be any "space" without particles and anti-particles?
juzzlin
CC BY-SA 4.0
2023-12-29T22:53:52.597Z
Yes.  These particles span the entirety of space.  You can not remove them.  They will still be there.  We do not know whether they “compose space” or not.
eshaya
CC BY-SA 4.0
2023-12-28T16:48:33.863Z
2023-12-28T16:48:33.863Z
ProfRob
<p>As with much in science, it is best to talk in terms of &quot;models&quot; rather than what something <strong>is</strong>. We can model a photon, for example, as a quantum excitation of the electromagnetic field.</p>
<p>Space is part of the model for doing physics. Together with time it is a coordinate system to describe locations, and the distances between locations.</p>
<p>The simplest model is &quot;Euclidian&quot; in which the positions are described by triplets of numbers <span class="math-container">$(x, y, z)$</span> and distance is <span class="math-container">$\sqrt{x^2+y^2+z^2}$</span>.</p>
<p>This is especially important in General Relativity as the &quot;curvature of spacetime&quot; is defined in terms of formulae for describing the distance between points (a &quot;metric&quot;).  In relativity spacetime is <span class="math-container">$(x,y,z,t)$</span>, and the distance has a more complex defintion.</p>
<p>You can conceive of empty space, and it is useful in some situations.  In particular there are important metrics that apply to empty space: The Minkowski metric of flat space, and the Schwatzchild metric of empty space around a  point mass.</p>
<p>So what <em>is</em> space(time), is a question for philosophers. How do we describe, use and model spacetime is a practical question with a specific answer. We can describe and model space using a coordinate system.</p>

CC BY-SA 4.0
2024-03-17T18:09:38.520Z
I have seen something similar to this before. thank you for your answer
WordPress Speed
CC BY-SA 4.0
2023-12-28T16:30:44.043Z
2023-12-29T16:19:39.767Z
2023-12-29T16:19:39.767Z
James K
<p>This is a philosophical rather than a scientific question. Space and time are not physical objects but forms of our existence. Without space no objects could exist, and without time no change of the configuration of physical objects (i.e. no motion) would be possible. You are effectively asking what the world would look like if there wasn't any world. That is a logical contradiction in terms.</p>

CC BY-SA 4.0
2023-12-31T17:31:48.227Z
Yes, but what does it mean that there's room to move?
juzzlin
CC BY-SA 4.0
2024-01-07T15:32:07.747Z
@juzzlin Well, it means that objects only have a finite size, so there is unoccupied space between them they can move into
Thomas
CC BY-SA 4.0
2023-12-28T18:46:37.323Z
2023-12-28T18:46:37.323Z
Thomas
<p>Physicists refer to space with no matter or energy (radiation) in it as <em>the vacuum</em>. You'd think that since it contains nothing, it would have no physical properties- but it does.</p>
<p>The vacuum propagates electric and magnetic fields in precisely measurable ways even though it contains no matter. For example, capacitors work even with vacuum between their plates which means space has a certain dielectric constant that is nonzero, even if its matter content is zero.</p>
<p>The study of the properties of the vacuum is an active field of physics research in which steady progress has been made over the years. Before quantum mechanics was discovered, what was known about the vacuum was summarized in a model called the <em>classical vacuum</em>, which was later replaced by the vacuum containing <em>quantum fields</em>. Check out wikipedia for more background on these topics.</p>

CC BY-SA 4.0
2024-03-17T07:09:31.060Z
2024-03-17T07:09:31.060Z
niels nielsen
<p>Consider a situation where <strong>everything</strong> is removed from the Universe. All matter, all radiation, everything.</p>
<p>Only a completely black void would remain. But what is it? What is this empty &quot;space&quot; that is nothing? Or would this nothing even exist without matter in the first place?</p>
<p>It is very hard to try to explain or imagine this.</p>
<p><strong>Edit:</strong> What I'm trying to ask is that what does it mean that there's room for particles to move? By &quot;space&quot; I don't mean the Universe, but <em>space</em>.</p>

CC BY-SA 4.0
2023-12-28T11:40:55.793Z
Related, possible duplicate: https://astronomy.stackexchange.com/q/13526/16685
PM 2Ring
CC BY-SA 4.0
2023-12-28T11:41:28.243Z
Also see https://physics.stackexchange.com/q/119591/123208 & links therein.
PM 2Ring
CC BY-SA 4.0
2023-12-28T14:14:06.840Z
What experiment could elucidate this? No experiment, no science...
John Doty
CC BY-SA 4.0
2023-12-28T14:15:42.350Z
So empty space is just a coordinate system? Hmm...not sure about that.
juzzlin
CC BY-SA 4.0
2023-12-28T14:17:03.250Z
Those links don't explain what does it mean that there is a volume.
juzzlin
CC BY-SA 4.0
2023-12-28T15:02:52.067Z
Perfectly empty space is an abstraction that exists only in your mind, so as long as your concept is mathematically consistent, it's good.
John Doty
CC BY-SA 4.0
2023-12-28T16:39:15.190Z
According to quantum mechanics, empty space or vacuum is  a foam of virtual particles, antiparticles, and EM waves randomly coming into and going out of existence.
eshaya
CC BY-SA 4.0
2023-12-28T18:33:25.007Z
@eshaya The OP wants these virtual particles obviously removed as well so that space is truly empty
Thomas
CC BY-SA 4.0
2023-12-29T15:49:21.573Z
Do these particles span the volume?
juzzlin
CC BY-SA 4.0
2023-12-29T16:19:02.993Z
"empty space is just a coordinate system" No ... but we can describe empty space using a coordinate system.
James K
CC BY-SA 4.0
2023-12-30T01:57:32.033Z
Space is space... because we call it like that! You kinda had such answer coming.
Mithoron
CC BY-SA 4.0
2024-03-24T00:40:52.937Z
@JohnDoty I think "No experiment, no science" is a little extreme, some theorists may disagree strongly.
uhoh
CC BY-SA 4.0
2024-03-24T01:15:32.080Z
@uhoh Some "physics" theorists belong in the theology department.
John Doty
CC BY-SA 4.0
2024-03-24T22:51:29.833Z
@JohnDoty I've never met one but I'll take your word for it. However, most theorists are *bona fide* scientists doing peer-reviewed *science*, some with data, many without. Take for example the early work on the possibility of black holes.
uhoh
CC BY-SA 4.0
2024-03-20T18:37:08.603Z
I’m voting to close this question because it is a philosophical question and not a physical or astronomical one.
Paul T.
CC BY-SA 4.0
2024-03-20T18:39:07.993Z
If you are interested in a historical/philosophical work on this subject, I would recommend "Concepts of Space: the history of theories of space in physics" by Max Jammer.
Paul T.
CC BY-SA 4.0
2024-03-21T19:21:43.837Z
@PaulT. No, this is not philosophical question as space (nothing) does exist.
juzzlin
<space-time><space>
What makes space space?
juzzlin
# What makes space space?

(Asked by: username_0 on 2023-12-28)

Consider a situation where **everything** is removed from the Universe. All matter, all radiation, everything.

Only a completely black void would remain. But what is it? What is this empty "space" that is nothing? Or would this nothing even exist without matter in the first place?

It is very hard to try to explain or imagine this.

**Edit:** What I'm trying to ask is that what does it mean that there's room for particles to move? By "space" I don't mean the Universe, but *space*.

**Tags:** space-time, space
> **Comments:**
> **username_1**: Related, possible duplicate: https://astronomy.stackexchange.com/q/13526/16685  
> **username_1**: Also see https://physics.stackexchange.com/q/119591/123208 & links therein.  
> **username_2**: What experiment could elucidate this? No experiment, no science...  
> **username_0**: So empty space is just a coordinate system? Hmm...not sure about that.  
> **username_0**: Those links don't explain what does it mean that there is a volume.  
> **username_2**: Perfectly empty space is an abstraction that exists only in your mind, so as long as your concept is mathematically consistent, it's good.  
> **username_3**: According to quantum mechanics, empty space or vacuum is  a foam of virtual particles, antiparticles, and EM waves randomly coming into and going out of existence.  
> **username_4**: @eshaya The OP wants these virtual particles obviously removed as well so that space is truly empty  
> **username_0**: Do these particles span the volume?  
> **username_5**: "empty space is just a coordinate system" No ... but we can describe empty space using a coordinate system.  
> **username_6**: Space is space... because we call it like that! You kinda had such answer coming.  
> **username_8**: I’m voting to close this question because it is a philosophical question and not a physical or astronomical one.  
> **username_8**: If you are interested in a historical/philosophical work on this subject, I would recommend "Concepts of Space: the history of theories of space in physics" by Max Jammer.  
> **username_0**: @PaulT. No, this is not philosophical question as space (nothing) does exist.  
> **username_7**: @JohnDoty I think "No experiment, no science" is a little extreme, some theorists may disagree strongly.  
> **username_2**: @uhoh Some "physics" theorists belong in the theology department.  
> **username_7**: @JohnDoty I've never met one but I'll take your word for it. However, most theorists are *bona fide* scientists doing peer-reviewed *science*, some with data, many without. Take for example the early work on the possibility of black holes.  

---

## 4 answers

### Answer by username_9 on 2023-12-28. Score: 3 | Accepted answer

There can be no such thing as "empty" space. Particles and anti-particles can and do pop into and out of existence on timescales that are shorter than $\sim \hbar/\Delta E$, where $\Delta E$ is the total energy (including rest mass) of the created particle/anti-particle pair.

Thus your thought experiment is impossible.

> **Comments:**
> **username_4**: The OP would obviously imply that these are removed as well. Otherwise space could not be called empty. It is only a hypothetical thought experiment after all, so you can imagine them being removed as well (some people actually think these vacuum fluctuations are tied in to matter)  
> **username_0**: Do this particles span the volume? There wouldn't be any "space" without particles and anti-particles?  
> **username_3**: Yes.  These particles span the entirety of space.  You can not remove them.  They will still be there.  We do not know whether they “compose space” or not.  

---

### Answer by username_5 on 2023-12-28. Score: 5

As with much in science, it is best to talk in terms of "models" rather than what something **is**. We can model a photon, for example, as a quantum excitation of the electromagnetic field.

Space is part of the model for doing physics. Together with time it is a coordinate system to describe locations, and the distances between locations.

The simplest model is "Euclidian" in which the positions are described by triplets of numbers $(x, y, z)$ and distance is $\sqrt{x^2+y^2+z^2}$.

This is especially important in General Relativity as the "curvature of spacetime" is defined in terms of formulae for describing the distance between points (a "metric"). In relativity spacetime is $(x,y,z,t)$, and the distance has a more complex defintion.

You can conceive of empty space, and it is useful in some situations. In particular there are important metrics that apply to empty space: The Minkowski metric of flat space, and the Schwatzchild metric of empty space around a point mass.

So what *is* space(time), is a question for philosophers. How do we describe, use and model spacetime is a practical question with a specific answer. We can describe and model space using a coordinate system.

> **Comments:**
> **username_10**: I have seen something similar to this before. thank you for your answer  

---

### Answer by username_4 on 2023-12-28. Score: 2

This is a philosophical rather than a scientific question. Space and time are not physical objects but forms of our existence. Without space no objects could exist, and without time no change of the configuration of physical objects (i.e. no motion) would be possible. You are effectively asking what the world would look like if there wasn't any world. That is a logical contradiction in terms.

> **Comments:**
> **username_0**: Yes, but what does it mean that there's room to move?  
> **username_4**: @juzzlin Well, it means that objects only have a finite size, so there is unoccupied space between them they can move into  

---

### Answer by username_11 on 2024-03-17. Score: -1

Physicists refer to space with no matter or energy (radiation) in it as *the vacuum*. You'd think that since it contains nothing, it would have no physical properties- but it does.

The vacuum propagates electric and magnetic fields in precisely measurable ways even though it contains no matter. For example, capacitors work even with vacuum between their plates which means space has a certain dielectric constant that is nonzero, even if its matter content is zero.

The study of the properties of the vacuum is an active field of physics research in which steady progress has been made over the years. Before quantum mechanics was discovered, what was known about the vacuum was summarized in a model called the *classical vacuum*, which was later replaced by the vacuum containing *quantum fields*. Check out wikipedia for more background on these topics.


---

