Light can break its own speed limit, researchers say

AI Thread Summary
Recent discussions highlight that light can exceed its traditional speed limit under specific conditions, particularly focusing on group velocity versus phase velocity in dispersive media. Participants emphasize that the speed of light varies depending on the medium, influenced by factors like pressure and temperature, but the fundamental speed of photons remains constant. Confusion arises around the terminology of phase and group velocity, with clarifications provided through analogies. The conversation also shifts to a critique of off-topic theories presented by one user, emphasizing the importance of maintaining focus on relevant scientific discussions. Overall, the thread underscores the complexities of light behavior and the need for clear communication in scientific discourse.
STAii
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I am really shocked !
http://www.cnn.com/2000/TECH/space/07/20/speed.of.light.ap/index.html is back to 2000 (i guess), but it is really shocking !
What do u people think ?
 
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Science news on Phys.org
Well...

The speed might be off a bit...but remember it depends on the medium the wave travels through. Light's speed may slightly vary depending on the pressure, desnity, temperature, and other basic properties of the medium it's send through.
 


Originally posted by anil
The speed might be off a bit...but remember it depends on the medium the wave travels through. Light's speed may slightly vary depending on the pressure, desnity, temperature, and other basic properties of the medium it's send through.
The refractive index of dense media has nothing to do with this experiment.

- Warren
 
The group velocity, not the phase velocity, is being "broken."
Can you please explain more ?

The speed might be off a bit...but remember it depends on the medium the wave travels through. Light's speed may slightly vary depending on the pressure, desnity, temperature, and other basic properties of the medium it's send through.
-The speed of light that you measure in any medium does not actually means that speed of the photon changed.
-Refraction index is always => 1 , therefore even the measured speed of light inside any medium will be <= c .
 
Originally posted by STAii
Can you please explain more ?
Did you read the link I provided?

- Warren
 
Well i tried to, but i didn't understand anything of it !
 
Originally posted by STAii
Well i tried to, but i didn't understand anything of it !
I thought the article was perhaps the clearest explanation of the experiment that I have seen in a long time.

If perhaps you're confused about the terms 'phase' and 'group' velocity, the explanation is simple.

Imagine a monochromatic (one color, one frequency) laser pulse. You could pick a spot, say the point of maximal electric field magnitude, and watch it propagate through space. Of course, the word "phase" simply refers to such a spot on a wave. Phase is measured in degrees or radians, and simply refers to an spot on a wave. The "phase velocity" is the speed at which a point of equal phase propagates through space. In the case of a laser, all of the wavefronts move through space at c, of course. No matter what phase you choose (anything from 0 to 360 degrees), you'd find that that points on the wave at that phase travel at c.

Things get more complicated when you combine light of different colors (frequencies) in a pulse. Each individual wavelength has its own independent phase velocity (of course, they're all c!) but the entire group of waves together appear to move in what is essentially an arbitrary way.

If you'll take a look at the applet on this page: http://www.ee.mu.oz.au/staff/summer/applets/group_velocity.html you'll get a feel for how things work. Set the group velocity to be about -0.1 and you'll see immediately how phase and group velocity are different. Both the red and green waves are moving forward at the same speed (same phase velocity). The sum of the two, which is the blue wave, is essentially moving BACKWARDS! This is the group velocity.

It's related to the well known effect that occurs when you watch car wheels spin on TV -- because TV shows you 30 frames per second, there are some wheel speeds at which the wheel will appear to be rotating backwards.

Let me know if you're still confused.

- Warren
 
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No thanks, i got it now.
It was the terms that actually made me feel confused.
I remembered a smiliar topic was discussed on PF 2.0 .
 
  • #10
Good day gentlemen,

Gravity controls all aspects of the four fundamental forces of nature at the quark level. Gravity-time can speed up for plasma desities creating hyperluminal photons and other superparticles that pass through time bubbles as hypergravity or light. When these events occour bosonic-fermion dynamics kick in, and eliminates it over a period for equvalency in time-gravity.
It is my opinion that the gluon, the neutrnio and the photon are all the same particle at different graviton levels. As time-gravity changes in transition to liquid and solids like that of stages of matter, from recreation to decay, the plasma has the same states as matter: gas, liquid and solid states.
When our star reaches quark energy plasma at its center manifolding takes place and slows down time in space dimensionally, this happens every 11 year cycle of solar flares, until the sun stops producing neutrinos that cut off the field that access hyperspace through subspace. So, when we speak of General Relativity, Einstein meant as
general in the sense of measurement, not general as part of sustinct
theory.
 
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  • #11
Originally posted by Kirk Gaulden
Gravity controls all aspects of the four fundamental forces of nature at the quark level... Einstein meant as
general in the sense of measurement, not general as part of sustinct
theory.
Don't ever post in the Physics forum again.

- Warren
 
  • #12
Originally posted by chroot
Don't ever post in the Physics forum again.

- Warren

As much as I might agree that the information might be a little erroneous, don't you think that the "Principals of 'Freedom of Speech'" should, at least allow, this person to post, with the inclusion that, you can, thereafter, explain why you think it is wrong!

After all, that is the only way to learn about people, them that are the purpose of the 'servitude', that Science, in general, seeks to serve.
 
  • #13
Originally posted by Mr. Robin Parsons
don't you think that the "Principals of 'Freedom of Speech'" should, at least allow, this person to post
No. This person hijacked a perfectly good thread about light experiments to jabber incoherently about his pet theory of gravity. I don't believe such behavior helps this group.

The freedom of speech ensures that one is legally entitled to have some have venue to express one's opinion -- it does not mean, however, that every venue must allow all speech.

- Warren
 
  • #14
I thought you wanted to learn. Good riddins.
 
  • #15
Yes...we wanted to learn. Good job chroot explaining this phenomenon.
 
  • #16
I'm no expert, but here is an analogy I quite like:

Two people are to carry a letter across a room (the room is ten metres across, for example). The information doesn't get to the far side of the room until it is carried there.

Person one takes 5-metre steps, each step taking 5 seconds.

Person two takes 1-metre steps, each step taking 1 second.

The second person is moving much faster than the first, yet it still takes ten seconds to get across the room.
 
  • #17
Originally posted by chroot

Don't ever post in the Physics forum again.

- Warren



Originally posted by Mr. Robin Parsons
don't you think that the "Principals of 'Freedom of Speech'" should, at least allow, this person to post

Originally posted by chroot
No. This person hijacked a perfectly good thread about light experiments to jabber incoherently about his pet theory of gravity. I don't believe such behavior helps this group.

Now is there a difference between telling someone to NOT post in the FORUMS again, and admonishing someone for the content of a thread??

Please, I would like to know.
 
  • #18
Originally posted by Mr. Robin Parsons
Now is there a difference between telling someone to NOT post in the FORUMS again, and admonishing someone for the content of a thread??

Please, I would like to know.
It's not an attack on the person (Kirk) -- it's an attack on the things he posts. Should he suddenly begin posting relevant and informative things, he will be welcomed. Of course, there's a snowball's chance in hell of that happening.

- Warren
 
  • #19
I agree with chroot. If we're talking about physics then this is the place. IF he wishes to start his own theory discussion, there's a lovely place called Theory Development. :)
 

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