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Is there a medium less dense than vacuum?
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If yes, light can travel faster than itself (as in vacuum) in that medium.
If no, can we make it?
special-relativity visible-light refraction vacuum faster-than-light
edited 1 hour ago
Qmechanic♦
98.8k121781089
asked 1 hour ago
Krishna Deshmukh
18528
add a comment |Â
up vote
2
down vote
favorite
If yes, light can travel faster than itself (as in vacuum) in that medium.
If no, can we make it?
special-relativity visible-light refraction vacuum faster-than-light
edited 1 hour ago
Qmechanic♦
98.8k121781089
asked 1 hour ago
Krishna Deshmukh
18528
add a comment |Â
up vote
2
down vote
favorite
up vote
2
down vote
favorite
If yes, light can travel faster than itself (as in vacuum) in that medium.
If no, can we make it?
special-relativity visible-light refraction vacuum faster-than-light
edited 1 hour ago
Qmechanic♦
98.8k121781089
asked 1 hour ago
Krishna Deshmukh
18528
If yes, light can travel faster than itself (as in vacuum) in that medium.
If no, can we make it?
special-relativity visible-light refraction vacuum faster-than-light
special-relativity visible-light refraction vacuum faster-than-light
edited 1 hour ago
Qmechanic♦
98.8k121781089
asked 1 hour ago
Krishna Deshmukh
18528
edited 1 hour ago
Qmechanic♦
98.8k121781089
asked 1 hour ago
Krishna Deshmukh
18528
edited 1 hour ago
Qmechanic♦
98.8k121781089
edited 1 hour ago
Qmechanic♦
98.8k121781089
edited 1 hour ago
Qmechanic♦
98.8k121781089
98.8k121781089
asked 1 hour ago
Krishna Deshmukh
18528
asked 1 hour ago
Krishna Deshmukh
18528
asked 1 hour ago
Krishna Deshmukh
18528
18528
add a comment |Â
add a comment |Â
4 Answers
4
active
oldest
votes
up vote
4
down vote
The answer would seem to be "no", because you make a medium less dense by removing material from it. Once you get to a vacuum, you are only left with how good is the vacuum?
An experiment for an undergraduate optics lab would be to build a Michelson interferometer with a gas cell in one arm. As the gas is pumped out, the interference fringes shift. You can actually calculate the change in the effective speed of light at different air pressures, and project how it would change as the pressure declines further and further.
The limiting value is the speed of light in a vacuum.
answered 1 hour ago
Peter Diehr
6,48811028
add a comment |Â
up vote
1
down vote
Is there a medium less dense than vacuum?
It depends from what you mean under vacuum. Let us take in account the local gravitational potential as a parameter of the vacuum. It is well known, that light follows the geodesic path of the space; neary massiv bodies the path of light is bended towards this body. But that is not the only phenomenon of the gravitational potential on light. Near massive bodies the light travels slower as far away from massive bodies.
If yes, light can travel faster than itself (as in vacuum) in that medium. If no, can we make it?
The speed of light is a local constant number and no any light (or any matter) can travel in vacuum faster than c. What is said above about different c is valid only for a observer in a position with different gravitational potential. For example light travels - from our location in space - near black holes slower and in empty deep space faster c.
answered 10 mins ago
HolgerFiedler
3,79131133
add a comment |Â
up vote
0
down vote
If you are talking about volume density, notice that "less density" does not imply a lower refractive index, although the correlation is often there. The Wikipedia page on the index gives some examples: https://en.wikipedia.org/wiki/Refractive_index#Density
I don't think it would make sense to assign any "density" to a vacuum, except for energy density, and I'm not aware of any absolute law relating any kind of density to the refractive index(except, of course, the optical density, of which it is a measure).
Now, it IS possible for the refractive index to be lower than one. The reason is that, when we talk about this index, we are talking about the change in phase speed, which can be greater than $c$ because it does not carry any information, and therefore there's no violation of relativity. Again, the Wikipedia page offers a good explanation and even some examples where the refractive index is
less than one :
https://en.wikipedia.org/wiki/Refractive_index#Refractive_index_below_unit
answered 15 mins ago
Othin
985
add a comment |Â
up vote
-1
down vote
It depends on volume! You have to read something about Casimir effect. Even in complete vacuum, you always have virtual particles. Reality is quantum, quantum vacuum is not empty! It cannot be!
So basically when volume is bounded as in capacitor, it seems there is less possible excitations inside ( less kinds of virtual particles ) than in general big volume.
It looks like there's a lot of vacuums density possible, and some of them are emptier than others, even if all of them are empty!
Casimir effect affects force between capacitor plates, and can be measured!
answered 54 mins ago
kakaz
1,294913
Does that affect the permeability or the permittivity of vacuum?
– Wolphram jonny
51 mins ago
add a comment |Â
4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
4
down vote
The answer would seem to be "no", because you make a medium less dense by removing material from it. Once you get to a vacuum, you are only left with how good is the vacuum?
An experiment for an undergraduate optics lab would be to build a Michelson interferometer with a gas cell in one arm. As the gas is pumped out, the interference fringes shift. You can actually calculate the change in the effective speed of light at different air pressures, and project how it would change as the pressure declines further and further.
The limiting value is the speed of light in a vacuum.
answered 1 hour ago
Peter Diehr
6,48811028
add a comment |Â
up vote
4
down vote
The answer would seem to be "no", because you make a medium less dense by removing material from it. Once you get to a vacuum, you are only left with how good is the vacuum?
An experiment for an undergraduate optics lab would be to build a Michelson interferometer with a gas cell in one arm. As the gas is pumped out, the interference fringes shift. You can actually calculate the change in the effective speed of light at different air pressures, and project how it would change as the pressure declines further and further.
The limiting value is the speed of light in a vacuum.
answered 1 hour ago
Peter Diehr
6,48811028
add a comment |Â
up vote
4
down vote
up vote
4
down vote
The answer would seem to be "no", because you make a medium less dense by removing material from it. Once you get to a vacuum, you are only left with how good is the vacuum?
An experiment for an undergraduate optics lab would be to build a Michelson interferometer with a gas cell in one arm. As the gas is pumped out, the interference fringes shift. You can actually calculate the change in the effective speed of light at different air pressures, and project how it would change as the pressure declines further and further.
The limiting value is the speed of light in a vacuum.
answered 1 hour ago
Peter Diehr
6,48811028
The answer would seem to be "no", because you make a medium less dense by removing material from it. Once you get to a vacuum, you are only left with how good is the vacuum?
An experiment for an undergraduate optics lab would be to build a Michelson interferometer with a gas cell in one arm. As the gas is pumped out, the interference fringes shift. You can actually calculate the change in the effective speed of light at different air pressures, and project how it would change as the pressure declines further and further.
The limiting value is the speed of light in a vacuum.
answered 1 hour ago
Peter Diehr
6,48811028
answered 1 hour ago
Peter Diehr
6,48811028
answered 1 hour ago
Peter Diehr
6,48811028
answered 1 hour ago
Peter Diehr
6,48811028
6,48811028
add a comment |Â
add a comment |Â
up vote
1
down vote
Is there a medium less dense than vacuum?
It depends from what you mean under vacuum. Let us take in account the local gravitational potential as a parameter of the vacuum. It is well known, that light follows the geodesic path of the space; neary massiv bodies the path of light is bended towards this body. But that is not the only phenomenon of the gravitational potential on light. Near massive bodies the light travels slower as far away from massive bodies.
If yes, light can travel faster than itself (as in vacuum) in that medium. If no, can we make it?
The speed of light is a local constant number and no any light (or any matter) can travel in vacuum faster than c. What is said above about different c is valid only for a observer in a position with different gravitational potential. For example light travels - from our location in space - near black holes slower and in empty deep space faster c.
answered 10 mins ago
HolgerFiedler
3,79131133
add a comment |Â
up vote
1
down vote
Is there a medium less dense than vacuum?
It depends from what you mean under vacuum. Let us take in account the local gravitational potential as a parameter of the vacuum. It is well known, that light follows the geodesic path of the space; neary massiv bodies the path of light is bended towards this body. But that is not the only phenomenon of the gravitational potential on light. Near massive bodies the light travels slower as far away from massive bodies.
If yes, light can travel faster than itself (as in vacuum) in that medium. If no, can we make it?
The speed of light is a local constant number and no any light (or any matter) can travel in vacuum faster than c. What is said above about different c is valid only for a observer in a position with different gravitational potential. For example light travels - from our location in space - near black holes slower and in empty deep space faster c.
answered 10 mins ago
HolgerFiedler
3,79131133
add a comment |Â
up vote
1
down vote
up vote
1
down vote
Is there a medium less dense than vacuum?
It depends from what you mean under vacuum. Let us take in account the local gravitational potential as a parameter of the vacuum. It is well known, that light follows the geodesic path of the space; neary massiv bodies the path of light is bended towards this body. But that is not the only phenomenon of the gravitational potential on light. Near massive bodies the light travels slower as far away from massive bodies.
If yes, light can travel faster than itself (as in vacuum) in that medium. If no, can we make it?
The speed of light is a local constant number and no any light (or any matter) can travel in vacuum faster than c. What is said above about different c is valid only for a observer in a position with different gravitational potential. For example light travels - from our location in space - near black holes slower and in empty deep space faster c.
answered 10 mins ago
HolgerFiedler
3,79131133
Is there a medium less dense than vacuum?
It depends from what you mean under vacuum. Let us take in account the local gravitational potential as a parameter of the vacuum. It is well known, that light follows the geodesic path of the space; neary massiv bodies the path of light is bended towards this body. But that is not the only phenomenon of the gravitational potential on light. Near massive bodies the light travels slower as far away from massive bodies.
If yes, light can travel faster than itself (as in vacuum) in that medium. If no, can we make it?
The speed of light is a local constant number and no any light (or any matter) can travel in vacuum faster than c. What is said above about different c is valid only for a observer in a position with different gravitational potential. For example light travels - from our location in space - near black holes slower and in empty deep space faster c.
answered 10 mins ago
HolgerFiedler
3,79131133
answered 10 mins ago
HolgerFiedler
3,79131133
answered 10 mins ago
HolgerFiedler
3,79131133
answered 10 mins ago
HolgerFiedler
3,79131133
3,79131133
add a comment |Â
add a comment |Â
up vote
0
down vote
If you are talking about volume density, notice that "less density" does not imply a lower refractive index, although the correlation is often there. The Wikipedia page on the index gives some examples: https://en.wikipedia.org/wiki/Refractive_index#Density
I don't think it would make sense to assign any "density" to a vacuum, except for energy density, and I'm not aware of any absolute law relating any kind of density to the refractive index(except, of course, the optical density, of which it is a measure).
Now, it IS possible for the refractive index to be lower than one. The reason is that, when we talk about this index, we are talking about the change in phase speed, which can be greater than $c$ because it does not carry any information, and therefore there's no violation of relativity. Again, the Wikipedia page offers a good explanation and even some examples where the refractive index is
less than one :
https://en.wikipedia.org/wiki/Refractive_index#Refractive_index_below_unit
answered 15 mins ago
Othin
985
add a comment |Â
up vote
0
down vote
If you are talking about volume density, notice that "less density" does not imply a lower refractive index, although the correlation is often there. The Wikipedia page on the index gives some examples: https://en.wikipedia.org/wiki/Refractive_index#Density
I don't think it would make sense to assign any "density" to a vacuum, except for energy density, and I'm not aware of any absolute law relating any kind of density to the refractive index(except, of course, the optical density, of which it is a measure).
Now, it IS possible for the refractive index to be lower than one. The reason is that, when we talk about this index, we are talking about the change in phase speed, which can be greater than $c$ because it does not carry any information, and therefore there's no violation of relativity. Again, the Wikipedia page offers a good explanation and even some examples where the refractive index is
less than one :
https://en.wikipedia.org/wiki/Refractive_index#Refractive_index_below_unit
answered 15 mins ago
Othin
985
add a comment |Â
up vote
0
down vote
up vote
0
down vote
If you are talking about volume density, notice that "less density" does not imply a lower refractive index, although the correlation is often there. The Wikipedia page on the index gives some examples: https://en.wikipedia.org/wiki/Refractive_index#Density
I don't think it would make sense to assign any "density" to a vacuum, except for energy density, and I'm not aware of any absolute law relating any kind of density to the refractive index(except, of course, the optical density, of which it is a measure).
Now, it IS possible for the refractive index to be lower than one. The reason is that, when we talk about this index, we are talking about the change in phase speed, which can be greater than $c$ because it does not carry any information, and therefore there's no violation of relativity. Again, the Wikipedia page offers a good explanation and even some examples where the refractive index is
less than one :
https://en.wikipedia.org/wiki/Refractive_index#Refractive_index_below_unit
answered 15 mins ago
Othin
985
If you are talking about volume density, notice that "less density" does not imply a lower refractive index, although the correlation is often there. The Wikipedia page on the index gives some examples: https://en.wikipedia.org/wiki/Refractive_index#Density
I don't think it would make sense to assign any "density" to a vacuum, except for energy density, and I'm not aware of any absolute law relating any kind of density to the refractive index(except, of course, the optical density, of which it is a measure).
Now, it IS possible for the refractive index to be lower than one. The reason is that, when we talk about this index, we are talking about the change in phase speed, which can be greater than $c$ because it does not carry any information, and therefore there's no violation of relativity. Again, the Wikipedia page offers a good explanation and even some examples where the refractive index is
less than one :
https://en.wikipedia.org/wiki/Refractive_index#Refractive_index_below_unit
answered 15 mins ago
Othin
985
answered 15 mins ago
Othin
985
answered 15 mins ago
Othin
985
answered 15 mins ago
Othin
985
985
add a comment |Â
add a comment |Â
up vote
-1
down vote
It depends on volume! You have to read something about Casimir effect. Even in complete vacuum, you always have virtual particles. Reality is quantum, quantum vacuum is not empty! It cannot be!
So basically when volume is bounded as in capacitor, it seems there is less possible excitations inside ( less kinds of virtual particles ) than in general big volume.
It looks like there's a lot of vacuums density possible, and some of them are emptier than others, even if all of them are empty!
Casimir effect affects force between capacitor plates, and can be measured!
answered 54 mins ago
kakaz
1,294913
Does that affect the permeability or the permittivity of vacuum?
– Wolphram jonny
51 mins ago
add a comment |Â
up vote
-1
down vote
It depends on volume! You have to read something about Casimir effect. Even in complete vacuum, you always have virtual particles. Reality is quantum, quantum vacuum is not empty! It cannot be!
So basically when volume is bounded as in capacitor, it seems there is less possible excitations inside ( less kinds of virtual particles ) than in general big volume.
It looks like there's a lot of vacuums density possible, and some of them are emptier than others, even if all of them are empty!
Casimir effect affects force between capacitor plates, and can be measured!
answered 54 mins ago
kakaz
1,294913
Does that affect the permeability or the permittivity of vacuum?
– Wolphram jonny
51 mins ago
add a comment |Â
up vote
-1
down vote
up vote
-1
down vote
It depends on volume! You have to read something about Casimir effect. Even in complete vacuum, you always have virtual particles. Reality is quantum, quantum vacuum is not empty! It cannot be!
So basically when volume is bounded as in capacitor, it seems there is less possible excitations inside ( less kinds of virtual particles ) than in general big volume.
It looks like there's a lot of vacuums density possible, and some of them are emptier than others, even if all of them are empty!
Casimir effect affects force between capacitor plates, and can be measured!
answered 54 mins ago
kakaz
1,294913
It depends on volume! You have to read something about Casimir effect. Even in complete vacuum, you always have virtual particles. Reality is quantum, quantum vacuum is not empty! It cannot be!
So basically when volume is bounded as in capacitor, it seems there is less possible excitations inside ( less kinds of virtual particles ) than in general big volume.
It looks like there's a lot of vacuums density possible, and some of them are emptier than others, even if all of them are empty!
Casimir effect affects force between capacitor plates, and can be measured!
answered 54 mins ago
kakaz
1,294913
answered 54 mins ago
kakaz
1,294913
answered 54 mins ago
kakaz
1,294913
answered 54 mins ago
kakaz
1,294913
1,294913
Does that affect the permeability or the permittivity of vacuum?
– Wolphram jonny
51 mins ago
add a comment |Â
Does that affect the permeability or the permittivity of vacuum?
– Wolphram jonny
51 mins ago
Does that affect the permeability or the permittivity of vacuum?
– Wolphram jonny
51 mins ago
Does that affect the permeability or the permittivity of vacuum?
– Wolphram jonny
51 mins ago
add a comment |Â
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