and light is always travelling at lightspeed faster than you...  that's what I get told.  and in the back of my head I was remembering hearing about something... scientists slowed light to the speed of a bicycle.. and so I was so glad to have found this video and I just have to wonder what it actually means. If light travels at different velocities through different materials and can actually be made to stop inside a cloud of supercooled atoms, then what is lights domain where it is always the fastest thing?

 

 

1 hour ago, sightseer said:

and light is always travelling at lightspeed faster than you

 

The speed of light is dependant on the density of the medium its traveling through. It can travel slower, just not faster than light speed. If you mean always traveling at light speed even if you yourself have a velocity and you, for example, shone a torch ahead of you, then Einstein told us that its time that's the variable to account for that. 

 

1 hour ago, sightseer said:

then what is lights domain where it is always the fastest thing

 

Light travels at light speed in a vacuum. The domain is a vacuum.

Might be worth mentioning the hypothetical Tachyon, which always travels faster than light. As I said, hypothetical. Most physicists would say they couldn't exist. But maybe, just maybe... 

Edited December 7, 20214 yr by martin-w

38 minutes ago, sightseer said:

and light is always travelling at lightspeed faster than you...  that's what I get told.  and in the back of my head I was remembering hearing about something... scientists slowed light to the speed of a bicycle.. and so I was so glad to have found this video and I just have to wonder what it actually means. If light travels at different velocities through different materials and can actually be made to stop inside a cloud of supercooled atoms, then what is lights domain where it is always the fastest thing?

Oh, you've found on one of my favourite physics experiments 🙂I remember well when that experiment was conducted in 1999, it was a big breakthrough, beautiful work. By now, scientists can even stop light in an atomic gas and retrieve it again ( https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.107.053603 ).

But to your question: a more precise statement about the speed of light is that "nothing can go faster than the (local) speed of light in vacuum". The speed of light when it travels through nothing is called c=299,793km/s and is fixed. c poses an absolute speed barrier for everything (almost, see below). Virtually all of modern physics would have to be rewritten if something would go faster. 

However, nothing prevents light from moving slower when it is inside a medium. An intuitive picture is that light gets absorbed by an atom, spends a little time in it (as a form of energy) and is then re-emitted. As a consequence, its velocity is slowed down compared to a vacuum. This is basically what the people in the paper above have done. There is a beautiful effect in nuclear reactors that is a consequence of this: https://en.wikipedia.org/wiki/Cherenkov_radiation . In the cooling water of a reactor, light only travels at about 2/3 c. The reactor can produce electrons that move faster than that (but still less than c). These electrons produce a blue glow in the water.

That's the short answer to your question. There are some ramifications that are worth mentioning: physicists distinguish between group velocity (the speed at which a short flash of light travels) and phase velocity (the speed at which light wiggles inside that flash) of light. The latter can actually be larger than the speed of light in vacuum, but since you can't use it to transfer information, there is no contradiction with relativity.

It gets even more weird: in a curved space-time, space itself can travel, and the speed of space itself is not bound. For instance, the Hubble law states that galaxies move away from us faster if they are farther away from us. The galaxies are carried along with space, and, as seen from us, space far away could move faster than the speed of light in vacuum. Hence, light emitted from some far away sources can actually appear to move at superluminal speed, even though locally (roughly, where it has been emitted), it always travels at c. We just perceive it as faster.

Peter

 

Quote

Nothing travels faster than the speed of light with the possible exception of bad news, which obeys its own special laws.

I believe Douglas Adams was correct.

Even heavy doesn't travel faster than light... except if it has a bigger surface area and its in an atmosphere.

💪🤪🤣

We know the speed of light because we found a way to measure it, but we don`t know what else is possible. We know the earth will die someday as will the sun new suns and planets are being formed, Astronomy tells us this.  

19 hours ago, Rob_Ainscough said:

The great part about science is never say never, it's doors are always open to change. 

Science is replete with 'We used to think, but now we know'.  And today's 'Now we know' becomes tomorrow's 'We used to think'.

I had once read that any body that reaches the speed of light will have infinite mass and zero length.  But that was years ago and might now be in the realm of 'We used to think'.

Noel

37 minutes ago, birdguy said:

Science is replete with 'We used to think, but now we know'.  And today's 'Now we know' becomes tomorrow's 'We used to think'.

 

True, but more often than not its... "We were more or less right but now we have fined tuned our theory to include..."

And there is plenty is science that hasn't been supplanted.

 

40 minutes ago, birdguy said:

I had once read that any body that reaches the speed of light will have infinite mass and zero length.  But that was years ago and might now be in the realm of 'We used to think'.

 

Nope, certainly not. Nobody has demonstrated that Einstein was wrong regarding mass increasing with velocity. 

Regarding length contraction its relative, relative to the observer. Its about frames of reference. 

 

"I need warp speed, now, Mr. Scott!" 🚀

https://www.msn.com/en-us/news/technology/researchers-accidentally-create-a-warp-bubble-the-first-step-in-faster-than-light-travel/vi-AARyXYg

48 minutes ago, charliearon said:

"I need warp speed, now, Mr. Scott!" 🚀

https://www.msn.com/en-us/news/technology/researchers-accidentally-create-a-warp-bubble-the-first-step-in-faster-than-light-travel/vi-AARyXYg

 

Is this for real? I know White, he's an warp drive/Alcubierre research guy for NASA.

I will be very angry if this is true! For weeks I have been beavering away in my shed, so if they have beat me to it, I'll be VERY angry! 

 

 

Quote

 

World's First 'Warp Bubble' Discovered by Serendipity? DARPA Researchers Find it in Strange Encounter

 

https://www.techtimes.com/articles/269047/20211207/worlds-first-warp-bubble-discovered-serendipity-darpa-researchers-find-strange.htm

 

 

Holy dog poo batman!!! 

It might be minuscule but if it is what they say... OMG! And I NEVER use the abbreviation OMG! 

If true, I don't think I have enough cat points to allocate. 

Edited December 8, 20214 yr by martin-w

Quote

In an interview with The Debrief earlier this week, White said that their serendipitous encounter with the warp bubble is not about it being a bubble analog. The specialist said that it was a real and tiny creation of its kind, making this accidental vision a significant breakthrough.

 

Pardon me for being sceptical, but I'm preparing myself for almost certain disappointment. 😐

White talks about pilot wave theory (Bohemian Mechanics) I must admit, pilot wave theory has always seemed more plausible to me but Then I'm no expert. 

 

 

Edited December 8, 20214 yr by martin-w

22 hours ago, Rob_Ainscough said:

It's all about the definition of "Nothing" ... the assumption is an object can't have negative mass.  Quantum electrodynamics is still a theory so the use of "Nothing" (and there is an entire separate topic path of exactly what is "nothing") needs further definition and understanding. 

The great part about science is never say never, it's doors are always open to change. 

"Science is a way of thinking much more than it is a body of knowledge" - Carl Sagan

Cheers, Rob.

And then there is quantum entanglement.  😎

 

Every black hole in the universe is probably due to local scientist's 'accidental' discoveries.

maybe the xenobots will find a way to ...

27 minutes ago, Rob_Ainscough said:

As you know from my videos, I'm in league with the Daleks

 

Are you saying your famous chiller runs on negative energy gifted you by the Daleks? 

5 hours ago, birdguy said:

Science is replete with 'We used to think, but now we know'.  And today's 'Now we know' becomes tomorrow's 'We used to think'.

I had once read that any body that reaches the speed of light will have infinite mass and zero length.  But that was years ago and might now be in the realm of 'We used to think'.

Noel

Newton's second law is 350 years old and is still valid. It explains most of the physics of flight, for instance. However, it is not considered a universally valid law anymore. It has its range of validity (very roughly anything larger than a micrometer to anything smaller than a galaxy), but it fails to describe larger structures or the realm of atoms and molecules. We have other laws for that, and those laws will for sure also have a limited range of validity. Time will tell.

The infinite mass and zero length is just a limiting case. In order to achieve that, you would have to put an infinite amount of energy into the body. Even the entire energy in the universe wouldn't suffice 🙂