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October. 26, 2020

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Re: SCIENCE
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Quote:

NeXoSE wrote:
Another question:

Will light faster than light?

Supposition:
We have a train on a straight track, and two high power flash lamps, One mounted and powered on the head of train, Other one fixed at start line of track and directing the end of track.

Then, set the train running and lamps started flashing. and we stand in the end line of the track.

Now, will the light on the train faster than the fixed one to enter our eye? Or keep same speed?

No, the light of both sources will be measured as c, as FF points out (c being shorthand for 'the speed of light' which is a constant). But the light from the source that is moving towards you will be blueshifted: it will carry more energy.

When a lightsource moves away from you, the light (which still, as always, travels at c) is redshifted.

This is the so-called Doppler effect, and it also occurs in the sirene of an ambulance or police car or firetruck, that passes you. When the car is getting nearer to you, the sirene is higher and faster, and when it is moving away from you, the sound wave is stretched, making the sirene sound slower and lower.

Posted on: 2011/9/24 17:08
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Re: SCIENCE
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Quote:

This is the so-called Doppler effect, and it also occurs in the sirene of an ambulance or police car or firetruck, that passes you. When the car is getting nearer to you, the sirene is higher and faster, and when it is moving away from you, the sound wave is stretched, making the sirene sound slower and lower.


This so reminded me of this

http://www.youtube.com/watch?v=Y5KaeCZ_AaY

Posted on: 2011/9/25 1:08
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Re: SCIENCE
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1) Remember that our knowledge of physics only describes 8 percent of the stuff in the galaxy. The other 92% does not obey our current "laws" of physics (dark matter, dark energy).

2) The theoretical speed limit is "the speed of light in a vacuum". It seems unsurprising that neutrinos might travel faster than the speed of light in the atmosphere.

3) Time dilation, and the theory that FTL matter moves backwards in time, assume that time is linear and ever-increasing. What if time is not always like that? We currently have no way to know.

We have very little experimental data about matter moving near the speed of light. It will not surprise me at all if we someday discover that our understanding of space-time and the speed-of-light "limit" are primitive.

Even our understanding of "matter" could change.



Posted on: 2011/9/25 13:14
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Re: SCIENCE
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You're sounding like you don't know much on the subject, Bullwinkle.

1) The hypothesis of dark matter and dark energy is not the sole possibility. There are many ways to explain the phenomena we see, some of which involve new matter types while others involve adapting current laws in specific cases. While we do not know everything, saying it this way is disingenuous because, as far as it matters, "normal matter" is what we care about most.

2) The measurement says it's faster compared to c, not to any slower speed.

3) You'll have to explain what you mean because you're just combining a lot of science-y sounding words in a sentence here.

We have in fact excellent data about neutrinos in the form of supernovae emissions, which confirmed our previous thought about the speed of neutrinos and light. Again, our understanding is not complete, but I'd be extremely surprised to see a fundamental change to the laws of physics we have defined some time in the future. Refining? Yes. Redefining? No.

Posted on: 2011/9/25 15:34
"Cynicism is not realistic and tough. It's unrealistic and kind of cowardly because it means you don't have to try."
-Peggy Noonan
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Re: SCIENCE
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Bullwinkle wrote:1) Remember that our knowledge of physics only describes 8 percent of the stuff in the galaxy. The other 92% does not obey our current "laws" of physics (dark matter, dark energy).

Hey BW, nice to see you

OT: dark matter is a fairly well described phenomenon. Dark energy is somewhat more vague. They both obey the current laws of physics. In a way you could say that they are 'plot devices' to make the observances and the established laws of physics fit eachother. I'm not super-convinced Dark Energy is really an objectively existing kinda stuff, or rather e.g. 'just' a byproduct of gravity which still needs to get tweaked into relativity's description of gravity..


Quote:

Bullwinkle wrote:

2) The theoretical speed limit is "the speed of light in a vacuum". It seems unsurprising that neutrinos might travel faster than the speed of light in the atmosphere.

If the results of that recent test could be explained that simple, I guess someone at CERN would have figured it out by now

Btw the speed of light is a constant, even in a non-vacuum - but in a non-vacuum (say, a glass wall or a body of water), the photons bump onto matter, so they take longer to get thru. But if you look at the speed of the photon in between these bumps, it's still going at c.

Iirc, it was in fact an experiment involving measuring light in the atmosphere which gave a strong and unexpected clue that the speed of light was a constant (Iirc, the idea was to measure the speed of light of the sunlight at sunrise as compared to the light of the sun at noon - the latter being expected to be faster. But it's quite some time ago that I read about it, and I might be oversimplifying or incorrect at points)


Quote:

Bullwinkle wrote:

3) Time dilation, and the theory that FTL matter moves backwards in time, assume that time is linear and ever-increasing. What if time is not always like that? We currently have no way to know.

We have very little experimental data about matter moving near the speed of light. It will not surprise me at all if we someday discover that our understanding of space-time and the speed-of-light "limit" are primitive.

Even our understanding of "matter" could change.

I overall agree with you on these statements. But I wanna add that the theoretic framework behind the scientific assumptions you mention, is not just some hypothesis on paper. It is a well-tested theory*, and applied in practice. The GPS systems of our cars work with it (because the satellites are less deep in Earth's gravity well, they 'experience' a slightly faster rate of time, as compared to us surface-dwellers. This time dilation has to be compensated for, in order for your GPS to be acurate - and this is achieved thru Relativity's formulas.)

*(Please note that the word 'theory' in scientific terminology, as opposed to every-day common use of the word, is not a synonym for hypothesis. A scientific theory has to meet a bunch of requirements to be valid; one of the requirements is that it has to be formulated in such a way that it can be proven false - if evidence against it arises - and it is true as long as it isn't proven false.)

Posted on: 2011/9/25 15:44
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Re: SCIENCE
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FriendlyFire wrote:

[...] I'd be extremely surprised to see a fundamental change to the laws of physics we have defined some time in the future. Refining? Yes. Redefining? No.

That's a very nice of putting it, FF! I can subscribe to that too.

(But, like I said in my reply to Bullwinkle, I won't be very surprised if Dark Energy would turn out to be a phenomenon being explained by a refinement in the Law of Gravity. (For what it's worth - which isn't much, as I'm not a scientist and not even very well educated in math... And 'gut-feelings' are of little use in the more advanced areas of science, which often deal with counter-intuitive phenomenons.))

Posted on: 2011/9/25 15:52
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Re: SCIENCE
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There are many theories that actually explain the effects of dark matter and dark energy without using either of them. Google for "Horava theory of gravity" for an example I've read about a few years ago

It's but one of many, but it goes to show there are always many ways to tackle an issue. Whether we end up finding out dark matter and energy to be true is something we won't know for some time, but it's always good *for things we are still uncertain about* to keep your mind open. In the case of the speed of light and neutrinos and relativity in general, we have just about no uncertainty, which is why scientists are so sceptical.

Posted on: 2011/9/25 17:47
"Cynicism is not realistic and tough. It's unrealistic and kind of cowardly because it means you don't have to try."
-Peggy Noonan
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