PigKnight
First Post
I C wut u did there.
But, for realsies, why is it called c? Latin? Kicks-n-giggles? Discovering scientist?
"Speed of Light"
I C wut u did there.
But, for realsies, why is it called c? Latin? Kicks-n-giggles? Discovering scientist?
Back in the mid to late 1800s, folks working on electromagnetism variously used "c" or "V" to stand for the speed of light (or, in some cases, a constant that happens to turn out to be related to the speed of light) - basically to stand for "constant" or "velocity". Over time, scientists just sort of drifted to using "c" as a standard notation, in large part because that's what a few of the Big Names of the time used.
The_Silversword
Explorer
Are photons really massless though? I mean theyre all the time getting sucked into black holes, if they had no mass a black hole wouldnt affect it, right?
tomBitonti
Adventurer
Hi,
I'm finding two (in the end, equivalent) explanations:
1) Gravity works on the total energy of an object.
For a detailed discussion, see:
http://en.wikipedia.org/wiki/Mass–energy_equivalence
Bold added by me.
2) Light always travels in straight lines. Or rather, since on a curved surface, "straight line" requires modification, light always travels along the shortest possible line between points. Then, gravity causes space-time to be curved, and the straight lines of light in gravitationally flat space are modified to the apparently curved lines in the curved space near a mass.
Here is a ho-hum explanation:
http://hubblesite.org/reference_desk/faq/answer.php.id=58&cat=exotic
Shortest lines in a curved space are called geodesics, with a basic definition, as an adjective "of, relating to, or denoting the shortest possible line between two points on a sphere or other curved surface."
In general relativity, there are special equations to describe geodesics, for example:
http://en.wikipedia.org/wiki/Geodesics_in_general_relativity
Lot's of heavy math, so be forewarned.
There are also definitions of "geodesic curve", for example (and also with heavy math):
http://math.stackexchange.com/questions/28690/which-is-the-proper-definition-of-a-geodesic-curve
"A shorted possible line between two points" works well as a common definition.
Thx!
TomB
GMMichael
Guide of Modos
Anyone else feel like the strange complications in this light theory are a hint at why we can't figure quantum physics out? Like, light is massless, yet light carries mass? Energy always travels at the same speed in a vacuum, even to observers moving at different speeds? "Energy carried by light," when light itself is supposed to be energy? Or if it's not energy, it must be matter. Even though light doesn't always behave like matter...
Does light actually slow down in different media, or does it simply take a longer path (by, say, reflecting off multiple particles resulting in a wandering, yet relatively straight, path)?
Does light actually slow down in different media, or does it simply take a longer path (by, say, reflecting off multiple particles resulting in a wandering, yet relatively straight, path)?
The_Silversword
Explorer
Ahh ok, #2 makes sense, #1 is a little harder for me to wrap my brain around.
The_Silversword
Explorer
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GMMichael
Guide of Modos
I read the article, and while I'm no physicist, I have to say that I'm not impressed.
Talking about the "speed" of light ties into another one of our quantum-physics problems: we don't much understand what Time is, either. We get a lot of great examples of the watch that doesn't turn as many times when it's close to the speed of light, or the person who doesn't age as much. But if the position of a watch's hands are what determines how much time has elapsed, then I can make time speed up or slow down with my pinky. Or if it's time that ages people, why all the anti-aging focus on anti-oxidants and other nutrients?
I'm sure the physicists are talking about the age of subatomic particles, not people and watches. But - does a photon have an age? Can a graviton be a spring chicken?
Yeah, both of tomBitonti's descriptions are reasonable ways to look at the situation.
For #1, we can try this.
Einstein told us E=mc^2. Energy and mass are interchangeable.
Most things we call physical matter have what's called a "rest mass". This is the mass of objects in your everyday experience - the mass you'd measure them having when they look to you like they are standing still (you are in their "frame of rest" or "rest frame"). By Einstein, then, an object at rest still has some energy just from being - we call that the object's "rest energy".
But Einstein's E is not particular. It applies to any and all energy the object has. If it has kinetic energy from moving, say, we add that to the bucket of total energy, and recalculate the mass. So, the faster the thing moves, the more effective mass it has.
Now, photons are screwy. When we say they don't have mass, what we really mean is that they don't have a rest mass. However you may be moving, the photon looks like it is moving at c relative to you. You *cannot* be in the rest frame of the photon, because you cannot move at its speed. But, it still has well-defined energy, and E=mc^2 still applies, so we can still think of it as interacting with gravity using that mass-from-energy.
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No, we have a pretty good handle on what Time is - at least as good a handle as what "space" is. Now, yes, there's some contention on what that really is down on what is known as the "Planck scale" - the very, very, super tiny down below the sizes of subatomic particles - but for most purposes if you grasp Relativity, you grasp what Time is.
Make the clock an atomic one, where the ticks are based on the ocillations of electrons in an atom, and no, you can't move the hands with your pinky any more. And, well, all those anti-aging creams don't work anyway, so why mention them?
No. And actually, THAT'S THE ENTIRE POINT!
Photons (gauge bosons, massless particles in general) are different from everything else in the Universe. All of relativity ultimately falls out from that one observationally verifiable fact. If you fire off an photon, it goes away from you at 186,000 mps. If you fire off a photon, and then strap the biggest rocket anyone could ever make to your butt, and take off after it, no matter how fast you go, it'll still be travelling away form you at 186,000 mps. It will also look like it is travelling the same speed away from Earth.
Relativity is the resolution of that apparent paradox - a viewer "at rest", and one moving wicked darn fast, both think the photon is moving at the same speed.
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