c
 

why is the speed of light independent of the speed of the observer and independent of the speed of the thing that emits the light?

Because. Just because.

Exactly!

Did your 5 year old ask you that?

"What is your favorite color"?

"Blue.....no, yel...."

Because all of the number crunching doesn't work if the speed of light is variable.

JR

The measured speed of light is relative to it's movement in the time/space continuum.

If we were driving our 911's at the speed of light, and then turned on our headlights.....

Thank you for responding after the OT equivalent of Technical's "What color should I paint my wheels" chimed in.

Can you expand on explaining the time/space continuum? Why do you think it's NECCESSARY that time runs at different rates depending on speed, and that mass increases as you go faster, and that the length of things decreases as you go faster (making these variables which, on the surface, seems completely antithetical to the human experience) all to preserve c being a wholly unique constant?

Two problems;

1) Travel at the speed of light requires "infinite" energy. Travel beyond the speed of light would require "infinite-plus" energy.

2) On the space/time continuum, travel at the speed of light would require no movement in the "time" axis. At the speed of light, time stands still. "Time" is an essential component of the measurement of relative speed.

A really elegant explanation of relativity and time dilation:

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And another on movement beyond the speed of light:

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Good stuff Moses....I'm impressed !!

There is no "Dopler" effect on light speed travel?

What is the airspeed velocity of an unladen swallow?

There is Doppler effect observable (i.e. "red-shifting" or "blue shifting") as entities move towards or away from one another at significant percentages of c.

Carl Sagan discussed what it might look like to travel very close to c in "Cosmos". The traveler would be viewed as highly red shifted when moving away from an observer and highly blue shifted when moving towards. The traveler would have a compressed field of vision (tunnel vision of sorts) due to their own light waves starting to pile up in front of them (similar to what happens with air as you approach the speed of sound).

I'll see if I can find a video of his brief explanation (it used an example of a guy on a scooter in the Italian countryside).

These are great. I'm off for the day, but somewhere between 5 and 6 minutes on the second video he says the Earth doesn't change its distance from the Sun due to the Law of Gravity. But since the sun is converting 4 million tons of matter per second into energy, the Earth would have to increase its distance from the Sun over time. I wonder what minimum mass the Sun would have to be to keep the Earth in orbit versus being pulled into the expansion of space.

As the sun's mass decreases the size of the earths orbit increases. At some point, the earth will be drawn to the gravitational field of a nearby heavier planetary mass and be drawn away from the present solar orbit completely.

I liked the videos, but the guy's voice is annoying as hell!

Hey! I narrated those vids... :mad:



KT :D

Funny... I was thinking the same thing. Not condescending, but like a 2nd grade teacher. Annoyingly melodic.

OHHH MY GAWD..I hope this is not going to happen anytime soon....I don't want to miss my restruant reservation, it is so hard to get in......

Relax tabby. Before that happens, the Sun will swell up like you at a buffet as its fusion process converts hydrogen into helium. The Sun will likely swell beyond the Earth's orbit, making the planet either scorched like Vegas, or it'll incinerate it like Yuma.

Just make sure you keep a healthy supply of SPF 1 Trillion. :)

"The sun is a mass of incadescent gas, a gigantic nuclear furnace, where hydrogen converts into helium at a temperature of millions of degrees....."

Why isn't "faster than a speeding bullet" enough?

because the two items you mention (source speed and observer speed) are negligible relative to the actual speed of light.

no. because time and distance are relative, and c = constant.

You absolutely have to install headlight relays before trying that.....

Distance is a function of time. All things, in a cosmological sense (according to Sir Hawking ), are moving away from each other. As such, the more time that elapses, the greater the distances between each. But, time can get distorted, as we know. Think visually. Imagine a one cubic inch of jello, any flavor will do. Now imagine two poppy seeds, somehow imbedded in the cube. Over time, the measurable distance between the seeds will change. Perhaps one seed is minutely more massive than the other so it "sinks" faster than the other (because the resistance of the jello holds the lesser massive seed stationary longer). Now, here's the part where you go "Huh?" Imagine the jello being "time". The movement of the poppy seeds, pushes the jello and compresses it, like a shock wave preceding a bullet, while the jello behind the seed decompresses forcing the jello to fill the vacuum which follows the seed (as in the cavitation of a prop on a boat). The jello is "distorted" by the movement of the seeds, just as time is distorted relative to the speed of an object as it approaches the speed of light.

Or, think even more visually, by turning the channel and watching something with Jennifer Aniston in it.

Chuck Norris counted to infinity, twice! ;)

From a practical perspective, what is the benefit to having c as a constant and time and space as variables in constructing our universe?

so how can photons travel at the speed of light?
if it requires Infitite energy to travel that fast?

E=mc^2

If a photon has no mass, how much energy do you think it takes to travel at a velocity = c?

A photon has no mass.

Actually, the energy of a photon is:

E = hc/lambda, where

lambda is the wavelength of the photon, and
h = 6.626*10-34 Js, and is a universal constant called Planck's constant

One additional clarification...photons do have some (tiny amount of) mass, but it's not a constant value. It's relative to the photon's momentum.

c has been observed to be constant. Therefore, time and space must be variable.

But if you're asking what the universe would be like if this were reversed, I don't know. I think c would no longer define a speed limit. Also, gravity works at the speed of light, so this roll-reversal might alter the laws of gravity.

But let's look at Einstein's famous equation, E=mc^2. In the reversed situation, E and m are constants, so c must be, also. So the equation doesn't work. Umm, is Stephen Hawking lurking here on Pelican?

I have a feeling that if c were variable, then electrical forces, including those that hold atoms together, would cease to be, and the whole universe would vaporize. There's you benefit to having c as a constant.

thanks Charlie. To the best of my recollection, light has not only been slowed down to highway speeds, but am pretty sure it has been stopped.

Well, sort of. ;)

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/960731.html

From Interview with Michael Turner, University of Chicago.

Q: Do photons have mass? If not, why does the gravitational field of a star bend passing light?

A: No, photons do not have mass according the present definition of mass. The modern definition assigns every object just one mass, an invariant quantity that does not depend on velocity, says Dr. Matt Austern a computer scientist at AT&T Labs Research. Under this definition, mass is proportional to the total energy, Eo, of the object at rest.

"A particle like a photon is never at rest and always moves at the speed of light; thus it is massless," says Dr. Michael S. Turner, chair of the Department of Astrophysics at the University of Chicago.

What about experimental evidence? Experiments don't determine exact quantities because of small errors inherent in making measurements. We have, however, put an upper limit on the photon rest mass. In 1994, the Charge Composition Explorer spacecraft measured the Earth's magnetic field and physicists used this data to define an upper limit of 0.0000000000000006 electron volts for the mass of photons, with a high certainty in the results.

This number is close to zero; it is equivalent to 0.00000000000000000000039 times the mass of an electron (the lightest particle), says Turner.

As I said, photon has a tiny amount of mass, that's not a constant value, and it's related to its momentum. ;)

It's a conundrum. It probably has mass, but the law of Relativity precludes it from having mass. Also, Newtonian mechanics do not support the notion of photon mass.

Anyway, it's only important in theoretical astrophysics.

IIRC, there was some work done on estimation of the upper limit of photon mass using "galactic" magnetic field interactions that suggested another 10 orders of magnitude smaller upper limit although don't ask me how you can measure galactic magnetic field dynamics from earth.