Why is the speed of light a constant?

last SG · 2009-12-31T13:57:13+00:00

Id like to make a correction to one of the ststements:"If we consider that electric field is an element(or whatever word you prefer), then it becomes clear s...

AndrewPKYap SG

Well, this actually has got nothing to do with my homework at all (in fact, I'm not even studying). But it's the closest forum I can find for my question.

The speed of Light is constant because time and distance (to put it simply) "changes" "to accommodate" (to put it simply) Light.

That is to say, if the distance is double (due to relativity, not static measurement) time would have slowed to half; the time it takes light to travel the doubled distance is half the "normal time it takes".

Therefore the speed of light remains constant.

You might think that this is ridiculous, that Time and distance can be relative because in your world (our world) Time and Distance is fixed.

Just as Newtonian gravity applies very well to earth (small objects) you need Einstein's gravity to apply to inter galactic objects.

AndrewPKYap SG

If you think all that is mind boggling, ...

....there are small (earth size) objects, large (intergalactic) objects ...and then there are QUANTUM objects... behaving differently hahahaha....

skythewood SG

Speed of light is constant is a theory. There are experiments and observations that validate this theory.

In simple terms, the experiment is something like this.

You travel in a space ship at 0.1 times the speed of light, for 10 months. When you come back to earth, you compare your time on the watch with your wife, you realize your watch registered 10 months has passed, but your wife one registered 1 year has passed.

And for both you and your wife, using your own equipment, you measured your speed to be 0.1 times the speed.

of course, the actual experiment was done at a more minor scale.

And they come up with the theory that time is not constant, but speed of light is.

coolgeek84 SG

You guys are mixing up general relativity and doppler effect and many other issues at the same time.

Speed of light is constant in a controlled environment. In this case, a vacum with zero or very low gravitational pulls.

Taking your train example, lets say there is a car travelling at 80kmph and the train is going at 120kmph. For a guy standing on ground both are 80 & 120 respectively, but for the guy on the train, the car is just going slower, perhaps 40kmph slower. But the fact is the car is still travelling 80kmph relative to the ground.

Speed of light is constant to a high extent in an environment with controlled variables.

You introduce Earth's atmosphere, gravitational pull e.t.c, then the speed is varied, but the variation is very negligible. Hence it is still approximated to be constant.

Only in presence of a black hole, the statement completely falls apart..

Mrruixiangz SG

LOL. It's hard to understand indeed.

Again, for example sake:

Let's say a observer is standing by the road (Guy A), and another person is inside a moving car (Guy B)

Let's say Guy B, while inside the moving car, throws a ping-pong ball forward and switch on a flashlight at the same time.

To Guy A, the ping-pong ball will seem to travel faster than it is to Guy B. Yet, to both observer, the light will seem to travel at the same speed?

Or is this example wrong in the first place cuz a ping-pong ball travels a gazillion time slower than light?

Huat ah!

Anyway, I've read about the LHC also. Apparently, it was ready a long time ago but has been delayed time and again due to many accidents (conspiracy theory: ppl from the future trying to sabotoge the experiment) as well as lawsuits. Others are afraid how it may destroy the world or something. Well...

There are people who were once scared the computers might destroy the world someday too.

Chew Bakar SG

Speed of light is a constant is an assumption with no interference of mass or other energy.

deepak.c SG

If the speed of light wasn't constant. Person A watching a light flash 1,000 km away would see it faster than Person B who is 10 km away. Why you ask?

Actually I think it would be kind of fun, don't you.

Chew Bakar SG

Depends on any masses between the point of origin and the observer. Only the moment of interior is justify as constant.

Fatum SG

Hey God ! ..... there's a question for you

Chew Bakar SG

Let there be light.

SBS2601D SG

The late 19th-century Michelson-Morley experiment first showed up the fact that light does not have a definite speed relative to its source.

eagle SG

Hi,

under the rules in Relativity by Einstein, nothing can ever move faster than the speed of light. Your question on the relative frames of motion is valid, and Einstein himself has had a similar thought experiment at the tender age of 16. He came out with his theory of relativity later on. His thought experiment: if person A were to throw a ball to person B faster than the speed of light.... then person B would see the ball both at his own hand and at person A's hand... Quite impossible...

I would suggest you read up on the theory of relativity. It's a very broad and interesting topic that few in the world can fully grasp it.

Do take note the equations for relativity. Relativistic concepts apply when things are travelling very close to the speed of light. The normal Newton's Laws of motion we learn at O and A levels do not apply for speeds very close to the speed of light... Instead, Einstein's equations of relativity will apply. In fact, if you simplify Einstein's equations of relativity with speeds very much lesser than the speed of light, you will get back Newton's Laws of Motion.

Also note that this has little to do with Doppler Effect. Doppler Effect is only for changes in frequency in different frames of motion. However, there's such a thing called relativistic Doppler Effect as well.

Lastly, Happy New Year!

Chew Bakar SG

Just a matter of interest.

The concept of calculus is a variation of small differences in a bigger curve. When compare with quantum is a small quantitative analysis of a bigger curve.

I believe this is the two sides of the same coin where everybody ignore the rim. This the moment of interior.

deepak.c SG

But seriously, at what c does it become a constant?

Is there like a specific crossover point like say 0.99 c?

Chew Bakar SG

--> c but never c.

Let close the year with a bang.

deathmaster SG

Speed of light do change in different mediums, due to different densities. e.g. vacuum> air> glass block.

so how can it be a constant?

deepak.c SG

Speed of light do change in different mediums, due to different densities. e.g. vacuum> air> glass block.

so how can it be a constant?

Light does not require a medium to transmit, it's not like sound.

Space is a vacumn, devoid of any medium. MM experiment was to find a medium for this, the so called ether.

dkcx SG

Light does not require a medium to transmit, it's not like sound.

Space is a vacumn, devoid of any medium. MM experiment was to find a medium for this, the so called ether.

It does not require a medium to transmit but if it passes through other mediums like air or liquid, its speed is slightly slowed down and not the same speed as that in vacuum.

deepak.c SG

It does require a medium to transmit but if it passes through other mediums like air or liquid, its speed is slightly slowed down and not the same speed as that in vacuum.

Ok, just found this out.

Certain materials have an exceptionally high group index and a correspondingly low group velocity for light waves, a phenomenon called slow light. In 1999, a team of scientists led by Lene Hau were able to slow the speed of a light pulse to about 17 metres per second (61 km/h; 38 mph);^[53] in 2001, they were able to momentarily stop a beam.^[54] In 2003, scientists at Harvard University and the Lebedev Physical Institute in Moscow, succeeded in completely halting light by directing it into a Bose–Einstein condensate of the element rubidium, the atoms of which, in Lukin's words, behaved "like tiny mirrors" due to an interference pattern in two "control" beams.^[55]^[56]

http://en.wikipedia.org/wiki/Speed_of_light#In_a_medium

deepak.c SG

http://en.wikipedia.org/wiki/Physical_constant

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