Calculating Relativity with Different Speeds: Vacuum or Medium?

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In summary, the effects of relativity are calculated based on the speed of light in a vacuum, which is also the maximum signal speed and the speed of a massless particle. Light traveling through a medium is affected by the scattering, absorption, and re-emission of atoms in the medium, causing it to travel at a slower speed. However, it is possible for an electron to move faster than the speed of light in a medium, such as water, due to the relativistic properties being based on the speed of light in a vacuum. This has been observed in water cooled nuclear reactors. Causality is more related to the maximum signal speed, which happens to equal the speed of light in vacuum.
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Hi, this is probably a silly question but I can't seem to find the answer anywhere:

are the effects of relativity calculated with reference to the speed of light in a vacuum or the speed of light in the medium in which you are traveling? For instance, if traveling in water, would the Lorentz factor be calculated based on c ≈ 3e8 or c ≈ 2.2 e8?
 
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Speed of light in a vacuum. The physics of light traveling through a medium are very different; the light is being continuously scattered, absorbed, re-emitted by the atoms of the medium. You could imagine the light being absorbed by an atom, then being re-emitted after a delay, traveling at c through the vacuum between atoms, then being absorbed and delayed again.

It's possible for a particle to travel through a medium at a speed greater than the speed of light in that medium; but not faster than c.

In fact, it would be more accurate to say that "c is the speed of a massless particle in a vacuum and light, being massless, travels at that speed in a vacuum" than "c is the speed of light". We don't, but that's for historical reasons - when relativity was being developed we didn't know about the other things that propagate with speed c.
 
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  • #3
As a result of the relativistic properties being based on the speed of light in vacuum, while it is not possible for an electron to move faster than the speed of light in vacuum, it is possible for an electron to move faster than the speed of light in water. That has been observed in water cooled nuclear reactors.
 
  • #4
HallsofIvy said:
As a result of the relativistic properties being based on the speed of light in vacuum, while it is not possible for an electron to move faster than the speed of light in vacuum, it is possible for an electron to move faster than the speed of light in water. That has been observed in water cooled nuclear reactors.

How is that possible? Seems to violate causality, and I guess mass/energy equivalence since the electron has a mass.

Is it better said as An electron can move faster than a photon through a medium under xyz conditions; both speeds are less than c*.

*speed of light in a vacuum
 
  • #5
Well, yes, the whole point is that the speed of light in water is less than the speed of light in vacuum. The whole point is that relativity uses the speed of light in vacuum and an electron can move faster than the speed of light in water. Look at https://en.wikipedia.org/wiki/Cherenkov_radiation
 
  • #6
nitsuj said:
How is that possible? Seems to violate causality, ...

It seems to me that Causality is related to the maximum signal speed.
The "speed of light in vacuum" happens to equal that maximum signal speed.

The speed of light and of other particles in a medium is more about their interactions with the medium... with causality only playing a role in setting an upper speed limit.
 

1. What is relativity in different media?

Relativity in different media refers to the concept of how the laws of physics, specifically the theory of relativity, apply differently in different environments. This includes the effects of gravity, time, and space in various mediums such as air, water, and vacuum.

2. How does relativity apply in different media?

Relativity applies in different media through the principle that the speed of light is constant in all frames of reference. This means that the laws of physics, including the theory of relativity, must hold true regardless of the medium in which they are observed.

3. Can relativity be observed in everyday life?

Yes, relativity can be observed in everyday life. For example, objects moving at high speeds will experience time dilation, meaning that time will pass slower for them compared to objects at rest. Additionally, the effects of gravity on time and space can also be observed in everyday life.

4. How does relativity in different media affect space travel?

Relativity in different media has a significant impact on space travel. For instance, the closer an object gets to the speed of light, the more time will slow down for that object. This means that astronauts traveling at high speeds will experience time differently than those on Earth, making precise calculations and adjustments crucial for successful space travel.

5. What are the implications of relativity in different media for our understanding of the universe?

The implications of relativity in different media have greatly expanded our understanding of the universe. The theory of relativity has helped us understand the effects of gravity on objects, the concept of time dilation, and the relationship between space and time. It has also played a crucial role in the development of technologies such as GPS and has allowed us to make predictions about the behavior of objects at extreme speeds or in different environments.

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