amnesia
Free-wheeling into oblivion...
- Location
- Bournemouth, Dorset
Everyone know's the speed of light ~ 186,000 miles per second.
What's the speed of DARK ???
What's the speed of DARK ???
Are there any physisists on the forum?
- Thread starter colly
- Start date
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XmisterIS
Purveyor of fine nonsense
amnesia said:
Dark is the absence of light, like cold is the absence of heat! Ya eejit ...
That's one of the examples I was thinking of. Though not quite accurate: it's not the Cerenkov radiation itself that goes FTL, but the particle passing through the dielectric, that causes the radiation (a sort of analogy of a sonic boon). The particle's going faster than the velocity of light in the dielectric (c/lambda) but still must be slower than c itself, the velocity of light in a vacuum. All particle and nuclear physicists are familiar with Cerenkov detectors.philipbh said:Is it too late to introduce Cerenkov Radiation - which travels faster through insulating mediums than the speed of light through the same medium.
I'm lost on this one: my physics is too rusty and too out-of-date (and I never got beyond U/G level anyway).Jim said:I have very limited knowledge in this field but came across this the other day...
http://www.sciencedaily.com/releases/2010/01/100126175921.htm
They use the word 'seem' a lot
I have one or two other examples of FTL in mind, I'll post them up if no-one else gets there first.
trustysteed
Guest
would it possibly be more accurate to state that at present we have found nothing that can travel faster than the speed of light but that something may exist that can, albeit as yet undiscovered?
Many thanks for all the interesting replies.
It is as I though.
I have to say there are some clever bods on here.
Pete I don't know what might travel faster than light. I did ask if anyone knew if gravity was instantaneous. Possibly the effect of gravity then. But then again I have heard of the search for 'gravity waves' so maybe not.
On a theme related to the original question:
Object A is travelling at 50% the speed of light,
Object B is travelling in the opposite direction at 50% the speed of light.
Is the speed 'relative' to one another the speed of light, 50% of that, or some other figure?
What if both objects are retreating from each other at 99.99% the speed of light
Would the light from A one travel to B at the speed of light relative to B?
Or would it arrive at a much slower speed?
Sorry with all the questions !!
It is as I though.
I have to say there are some clever bods on here.
Pete I don't know what might travel faster than light. I did ask if anyone knew if gravity was instantaneous. Possibly the effect of gravity then. But then again I have heard of the search for 'gravity waves' so maybe not.
On a theme related to the original question:
Object A is travelling at 50% the speed of light,
Object B is travelling in the opposite direction at 50% the speed of light.
Is the speed 'relative' to one another the speed of light, 50% of that, or some other figure?
What if both objects are retreating from each other at 99.99% the speed of light
Would the light from A one travel to B at the speed of light relative to B?
Or would it arrive at a much slower speed?
Sorry with all the questions !!
colly said:
So gravitons if they exist are believed to move at c because they are massless. They are massless because they apparently act without limit (think how far away the sun is or another galaxy). As for LIGO and searching for gravity waves as I understand it people have been somewhat disappointed with the lack of results so far but that they are making it more sensitive and hope to see something in a few years time.
I don't know about gravity waves (others can answer this better) but I think the answer is, not instantaneous.colly said:
Use the formula (posted above). For your example the answer is (0.5+0.5)(1+0.5^2) = 0.8, i.e. the closing speed is 80% c.
Light, in a vacuum, is always seen as travelling at 'c', regardless of the speed of the observer. That is the fundamental principle on which Special Relativity is based. Indeed it was deduced from the Michelson-Morley experiment, back in 1887, long before Einstein got involved, although Einstein provided the proper explanation.
Night Train
Maker of Things
- Location
- Greater Manchester
Same as the speed of light.amnesia said:
If you had a point source of light, and then extingished the light, the dark would follow along the same path as the last photon of light at the same speed.
I browsed a 'new' magazine the other day at the supermarket and it was something about science answers.
In there was a question about light when moving at or near the speed of light.
The answer said that if you were moving at or near the speed of light and switched on a torch you would not see any difference in the beam of light from the torch.
Surely, apart from the actual 'being there to see it' the beam of light from the torch would be relatively slower in the direction of travel.
Say the torch was moving at 1mph less then the speed of light and was then switch on. That beam of light from the torch would exit the lense at 1mph relative to the torch body and the observer holding the torch.
It was an OU example of determining the difference between the experience of gravity on a large slow or static body and that experienced through continuous acceleration in a moving craft.
In the moving craft the speed of light in the direction of travel, ie upwards against the psudo gravity, would appear to be slower then it would be on a static body.
However, that would appear to ignore the affects of real gravity on light.
Night Train
Maker of Things
- Location
- Greater Manchester
I would be sad enough to be interested. And I would read it.MichaelM said:
I will pm you.
Flying_Monkey
Recyclist
- Location
- Odawa
I'm pretty sure I was reading about a theorist the other day who seems to have shown that gravity doesn't actually exists (at least not in the sense that there will be either gravitons or gravity waves that we can discover)...
Davidc
Guru
- Location
- Somerset UK
marinyork said:
Yes it was.
I don't think his work is out as a peer reviewed paper yet though. I'll probably look at a review of it, but can't say I find theories of gravity rivetingly exciting!
FM, I doubt he's suggesting gravity doesn't exist (unless he's inexplicably floated off into space), more likely, like Einstein, he'll be saying it's an artefact of something else.
I just want to be able to turn it down when cycling uphill.
twentysix by twentyfive
Clinging on tightly
- Location
- Over the Hill
Things Faster that the speed of light in vacuum:-
Phase velocity of a wave. Picture a wave at the sea side breaking on the beach. If the wave is at an angle to the beach then the contact of the crest with the beach appears to travel along the beach at a speed determined by the angle and the speed of the wave. Now what happens to that speed when the wave is parallel to the beach? Anyone accept infinite speed? Infinity being larger that 3*10^8 m/s (light speed). This curiosity does not defy Relativity Theory as no information is carried by the phase of a wave.
Then there is the puzzle of entangled states which someone referered to above. The measurement on one particle defines the "state" of a very distant but connected particle instantaneously. Einstein hated this but subsequently Bell's Theorem and many experiments have shown it to be true. Spooky action at a distance. And this does appear to defy Relativity Theory as information appears to be transferred instantaneously.
Pete - were these the 2 you were thinking of - or is there another I've forgotten
Phase velocity of a wave. Picture a wave at the sea side breaking on the beach. If the wave is at an angle to the beach then the contact of the crest with the beach appears to travel along the beach at a speed determined by the angle and the speed of the wave. Now what happens to that speed when the wave is parallel to the beach? Anyone accept infinite speed? Infinity being larger that 3*10^8 m/s (light speed). This curiosity does not defy Relativity Theory as no information is carried by the phase of a wave.
Then there is the puzzle of entangled states which someone referered to above. The measurement on one particle defines the "state" of a very distant but connected particle instantaneously. Einstein hated this but subsequently Bell's Theorem and many experiments have shown it to be true. Spooky action at a distance. And this does appear to defy Relativity Theory as information appears to be transferred instantaneously.
Pete - were these the 2 you were thinking of - or is there another I've forgotten
twentysix by twentyfive
Clinging on tightly
- Location
- Over the Hill
Jim said:I have very limited knowledge in this field but came across this the other day...
http://www.sciencedaily.com/releases/2010/01/100126175921.htm
They use the word 'seem' a lot
A quick scan through this and I think the answer lies in the Heisenberg Uncertainty Principle - Delta E * Delta t ~ h bar. ie there will be a spread of photon arrival times (t) around the value calculated using the speed of light in the structure. The structure is effectively a form of energy (E) filter with appropriate probabilities of transmission. In the case of a single photon it will either be "lucky" and get through or not. The "luck" depends on the value of the photon energy. So some will get through "early" and some "late" but most get through exactly on "time".
