What is a vacuum?

[geordief]

In science I think the answer may simply be a region of space where nothing is measured (perhaps I am wrong and it is not simple at all)

Are there any other ways of defining a vacuum ?

I recall that topological  types boil down to how many "holes" there are in the overall shape. Might  these "holes" have any  bearing on what a vacuum is?

[trevorjohnson32]

47 minutes ago, geordief said:

Are there any other ways of defining a vacuum ?

Wouldn't it be more like a region where there is no air molecules? you can have a vacuum with a gravity field in it and its still a vacuum.

[beecee]

2 hours ago, geordief said:

In science I think the answer may simply be a region of space where nothing is measured (perhaps I am wrong and it is not simple at all)

Are there any other ways of defining a vacuum ?

I recall that topological  types boil down to how many "holes" there are in the overall shape. Might  these "holes" have any  bearing on what a vacuum is?

Even inter planetary space, or interstellar space is not quite a pure vacuum by definition, but getting pretty damn close I would say.

definition: Space in which there is no matter or in which the pressure is so low that any particles in the space do not affect any processes being carried on there. It is acondition well below normal atmospheric pressure and is measured in units of pressure (the pascal). https://www.quora.com/What-is-a-vacuum-condition

Edited January 18, 2018 by beecee

[swansont]

There are multiple definitions of vacuum.

One is the complete absence of matter, sometimes called an ideal or pure vacuum. A variant of that also includes the absence of photons. Another is a region where the pressure is significantly lower than atmosphere; this what one is usually referring to when using the word.

I'm not aware of any direct connection to topology.

[mistermack]

Maybe you could define a vacuum as a volume of space through which light always travels in a straight line at c. Anything else is a partial vacuum. 

Except in a gravitational field, when it follows the curve of space time at c.

Having said that, if you test it with a photon, it's no longer an absolute vacuum. 

[StringJunky]

How about: a vacuum is a volume absent of pressure.

[geordief]

1 hour ago, mistermack said:

Maybe you could define a vacuum as a volume of space through which light always travels in a straight line at c. Anything else is a partial vacuum. 

Except in a gravitational field, when it follows the curve of space time at c.

Having said that, if you test it with a photon, it's no longer an absolute vacuum. 

Would it not  no longer  be an absolute vacuum only at the point the photon was actually detected?

Photons don't have a path ,do they?

Do vacuums also exist in the empty spaces within atoms ?

[swansont]

Because virtual particles pop into and out of existence everywhere, it makes no sense to talk of an empty space within atoms.

Rule 1. A perfect vacuum doesn't exist. 
If you have a question about a perfect vacuum, see rule 1.

[Country Boy]

On ‎1‎/‎18‎/‎2018 at 6:23 AM, mistermack said:

Maybe you could define a vacuum as a volume of space through which light always travels in a straight line at c. Anything else is a partial vacuum. 

Except in a gravitational field, when it follows the curve of space time at c.

Having said that, if you test it with a photon, it's no longer an absolute vacuum. 

Well, that sort of thing happens with every measurement.  If you put a thermometer in a bowl of water to measure its temperature, you change the temperature.  When you put an air-gauge on a tire to measure its air pressure, you let some air out so change the air pressure by measuring it.

[Mordred]

On 18/01/2018 at 7:27 AM, geordief said:

Would it not  no longer  be an absolute vacuum only at the point the photon was actually detected?

Photons don't have a path ,do they?

Do vacuums also exist in the empty spaces within atoms ?

Under Cosmology applications, as Swansont mentioned above the definitions vary. The vacuum is a scalar field with no inherent average directional component. The mean energy density itself can be greater or less than the mean ground state ie positive/negative vacuum. The ground state would be some arbitrary baseline state that is set at zero mathematically. Though its true value can be a nonzero energy/mass density.

Edited January 27, 2018 by Mordred

[interested]

On 1/18/2018 at 1:43 PM, swansont said:

Because virtual particles pop into and out of existence everywhere, it makes no sense to talk of an empty space within atoms.

Rule 1. A perfect vacuum doesn't exist. 
If you have a question about a perfect vacuum, see rule 1.

Could an area of empty space exist without quantum fluctuations to support it. ie does space need quantum fluctuations in the form of virtual particles/gravitons to support it. When gravity waves pass by LIGO space expands and contracts. How would you define an area of space for a perfect vacuum if the volume changes depending on the amount of gravity that it experiences. Absolute zero can not be reached because of virtual particles popping into and out of existence, if they stopped popping into and out existence would that space still exist. ?

Rule 1. A perfect vacuum can not exist because if their was no virtual particles popping into and out of existence in an area of space then that space would not exist either ? Maybe  

[StringJunky]

49 minutes ago, interested said:

Could an area of empty space exist without quantum fluctuations to support it. ie does space need quantum fluctuations in the form of virtual particles/gravitons to support it. When gravity waves pass by LIGO space expands and contracts. How would you define an area of space for a perfect vacuum if the volume changes depending on the amount of gravity that it experiences. Absolute zero can not be reached because of virtual particles popping into and out of existence, if they stopped popping into and out existence would that space still exist. ?

Rule 1. A perfect vacuum can not exist because if their was no virtual particles popping into and out of existence in an area of space then that space would not exist either ? Maybe  

Space is volume. Volume does not exist by itself because it is a property of things. It should be easy to see that space isn't a thing of itself. i think, probably, a volume of virtual particles is the emptiest you can get.

[swansont]

14 hours ago, interested said:

Could an area of empty space exist without quantum fluctuations to support it.

Space does not need virtual particles to "support" it. 

 

[interested]

8 hours ago, swansont said:

Space does not need virtual particles to "support" it. 

 

Does space exist anywhere without virtual particles? 

Could an area of space be generated without virtual particles in it, or in some way remove them, I think not.

21 hours ago, StringJunky said:

i think, probably, a volume of virtual particles is the emptiest you can get.

I think I agree. However the volume of space is affected by gravity waves as seen by ligo, these gravity waves alter the dimensions of everything they pass

What was intriguing me was if an amount of quantum fluctuations could be reduced or absorbed in someway would it cause a distortion of space like gravity would the volume of space decrease or increase with less or more quantum fluctuations or virtual gravitons. Could quantum fluctuations of one form or another appearing in space away from mass be the cause of dark energy. Could those be virtual gravitons. 

 

Edit could just over the event horizon of a black hole be considered a perfect vacuum or does hawking radiation stuff that thought.

 

Edited March 6, 2018 by interested

[interested]

On 3/6/2018 at 6:06 PM, interested said:

Does space exist anywhere without virtual particles? 

Could an area of space be generated without virtual particles in it, or in some way remove them, I think not.

I think I agree. However the volume of space is affected by gravity waves as seen by ligo, these gravity waves alter the dimensions of everything they pass

What was intriguing me was if an amount of quantum fluctuations could be reduced or absorbed in someway would it cause a distortion of space like gravity would the volume of space decrease or increase with less or more quantum fluctuations or virtual gravitons. Could quantum fluctuations of one form or another appearing in space away from mass be the cause of dark energy. Could those be virtual gravitons. 

 

Edit could just over the event horizon of a black hole be considered a perfect vacuum or does hawking radiation stuff that thought.

 

I dunno, but some clever folk suggest I might be partly right. I will give myself a mark for trying. 

Has any one got any idea how the vacuum of space would behave with 8 possible spacial dimensions as in string theory. Simply I would say much like space behaves today, with virtual particles/quantum fluctuations appearing to appear from nowhere and disappear again, governed by some uncertainty or other principle.

 

 

[geordief]

15 minutes ago, interested said:

 Simply I would say much like space behaves today, with virtual particles/quantum fluctuations appearing to appear from nowhere and disappear again, governed by some uncertainty or other principle.

 

 

What does govern these"virtual particle/quantum fluctuations" ?Are they a property of the vacuum or of the  matter in the environment?

(perhaps SJ suggested the latter....?)

 

 

[StringJunky]

1 hour ago, geordief said:

What does govern these"virtual particle/quantum fluctuations" ?Are they a property of the vacuum or of the  matter in the environment?

(perhaps SJ suggested the latter....?)

 

 

From what I, vaguely, understand, if the virtual particles have sufficient energy, as an ensemble, they can configure into measurable particles. Any particle less than a quantum cannot persist and are called 'virtual'.  From Wiki:

Quote

Vacuum State

In quantum field theory, the quantum vacuum state (also called the quantum vacuum or vacuum state) is the quantum state with the lowest possible energy. Generally, it contains no physical particles. Zero-point field is sometimes used as a synonym for the vacuum state of an individual quantized field.

According to present-day understanding of what is called the vacuum state or the quantum vacuum, it is "by no means a simple empty space".[1][2] According to quantum mechanics, the vacuum state is not truly empty but instead contains fleeting electromagnetic waves and particles that pop into and out of existence.[3][4][5]     https://en.wikipedia.org/wiki/Vacuum_state

 

Edited March 8, 2018 by StringJunky

[interested]

12 hours ago, StringJunky said:

the vacuum state is not truly empty but instead contains fleeting electromagnetic waves and particles that pop into and out of existence

Are these particles just virtual particles perhaps due to wave interactions forming a peak giving sufficient energy to appear as a particle but are in fact just interacting waves passing each other in opposite directions perhaps? If they exist only fleetingly could they be the missing mass attributed to dark matter in the universe, ie they are there on average if you take the RMS value of a sine waveform you have a value that otherwise would be zero if you only took the mean.

Edit Things might appear to pop into and out of existence for someone living in a flatland could 4 dimensional space be considered flatland when looking at string theory

Edited March 9, 2018 by interested

[Strange]

34 minutes ago, interested said:

Are these particles just virtual particles perhaps due to wave interactions forming a peak giving sufficient energy to appear as a particle but are in fact just interacting waves passing each other in opposite directions perhaps?

In quantum theory there is no distinction between waves and particles. What we call particles are just the quantised amplitudes of waves. Because of the uncertainty principle, there is a possibility for the non-zero energy of the vacuum to reach the level of a pair of virtual particles (for a limited time, as defined by the uncertainty principle).

Quote

If they exist only fleetingly could they be the missing mass attributed to dark matter in the universe, ie they are there on average if you take the RMS value of a sine waveform you have a value that otherwise would be zero if you only took the mean.

They appear because of the non-zero vacuum energy. They don't contribute extra energy. 

Also, dark matter is concentrated (e.g. in galaxies) whereas the vacuum energy is the same everywhere.