<p><a href="https://en.wikipedia.org/wiki/Cherenkov_radiation" rel="nofollow noreferrer">Cherenkov radiation</a> (Wikipedia)</p>

<blockquote>
  <p>Cherenkov radiation, also known as Vavilov–Cherenkov radiation,[a] is electromagnetic radiation emitted when a charged particle (such as an electron) passes through a dielectric medium at a speed greater than the phase velocity of light in that medium. The characteristic blue glow of an underwater nuclear reactor is due to Cherenkov radiation. It is named after Soviet scientist Pavel Alekseyevich Cherenkov, the 1958 Nobel Prize winner who was the first to detect it experimentally.<a href="https://en.wikipedia.org/wiki/Cherenkov_radiation" rel="nofollow noreferrer">1</a> A theory of this effect was later developed within the framework of Einstein's special relativity theory by Igor Tamm and Ilya Frank, who also shared the Nobel Prize. Cherenkov radiation had been theoretically predicted by the English polymath Oliver Heaviside in papers published in 1888–89.</p>
</blockquote>

<p><a href="https://i.sstatic.net/YbAjT.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/YbAjT.jpg" alt="Eerie blue glow"></a></p>

CC BY-SA 3.0
2015-09-06T22:10:37.073Z
2015-09-06T22:10:37.073Z
Wayfaring Stranger
<p>It is a said fact that 299792458 m/s is the speed limit,nothing can go faster than this speed, or it will take an infinite amount of energy for propulsion.What we perforce in vacuum is one thing.Can someone explain what will be observed(from the particle's frame and an observer frame at rest) if a particle of a non zero test mass moves at light speed inside a non vacuum medium(say water) as this velocity is definitely lesser than the limit.
THANKS IN ADVANCE </p>

CC BY-SA 3.0
2015-09-06T17:57:00.530Z
This might be better on Physics Stack Exchange, especially as it relates to [one of your questions there](http://physics.stackexchange.com/questions/205553/alongside-a-light-ray-in-another-medium).
HDE 226868
CC BY-SA 3.0
2015-09-06T17:57:18.270Z
I'm voting to close this question as off-topic because it is about physics, not astronomy.
HDE 226868
CC BY-SA 3.0
2015-09-06T18:18:52.887Z
It was intended for the physics website somehow it ended up here
Abhinav
<light><general-relativity><speed>
Travelling at light speed(inside water)
Abhinav
# Travelling at light speed(inside water)

(Asked by: username_0 on 2015-09-06)

It is a said fact that 299792458 m/s is the speed limit,nothing can go faster than this speed, or it will take an infinite amount of energy for propulsion.What we perforce in vacuum is one thing.Can someone explain what will be observed(from the particle's frame and an observer frame at rest) if a particle of a non zero test mass moves at light speed inside a non vacuum medium(say water) as this velocity is definitely lesser than the limit.
THANKS IN ADVANCE

**Tags:** light, general-relativity, speed

> **Comments:**
> **username_1**: This might be better on Physics Stack Exchange, especially as it relates to [one of your questions there](http://physics.stackexchange.com/questions/205553/alongside-a-light-ray-in-another-medium).  
> **username_1**: I'm voting to close this question as off-topic because it is about physics, not astronomy.  
> **username_0**: It was intended for the physics website somehow it ended up here  

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## 1 answers

### Answer by username_2 on 2015-09-06. Score: 5 | Accepted answer

[Cherenkov radiation](https://en.wikipedia.org/wiki/Cherenkov_radiation) (Wikipedia)

> Cherenkov radiation, also known as Vavilov–Cherenkov radiation,[a] is electromagnetic radiation emitted when a charged particle (such as an electron) passes through a dielectric medium at a speed greater than the phase velocity of light in that medium. The characteristic blue glow of an underwater nuclear reactor is due to Cherenkov radiation. It is named after Soviet scientist Pavel Alekseyevich Cherenkov, the 1958 Nobel Prize winner who was the first to detect it experimentally.[1](https://en.wikipedia.org/wiki/Cherenkov_radiation) A theory of this effect was later developed within the framework of Einstein's special relativity theory by Igor Tamm and Ilya Frank, who also shared the Nobel Prize. Cherenkov radiation had been theoretically predicted by the English polymath Oliver Heaviside in papers published in 1888–89.

[![Eerie blue glow](https://i.sstatic.net/YbAjT.jpg)](https://i.sstatic.net/YbAjT.jpg)


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