Does light really have a speed?

Question

I think the speed of light can be misleading. It causes one to think that light accelerates -to or radiates-at its max speed. Which is roughly around 186,000km per second in a vaccum also referred to as (c). Is this an objective measurement? Perhaps 186,000km per second (Speed of electromagnetic radation in vaccum) is the fastest that our eyes/brain can register lights information? The data has to be there before we can receive it, correct? Perhaps this is why the speed of light is the same in all refrence frames? Does light really have a speed? They say that it travels at different speeds in different mediums, right? Faster in a vaccum and slower in air. So if light travels in a vaccum, through air, back in a vaccum, through air - its speed will accelerate/decelerate according to the medium? Thats like a bullet traveling faster when it exists a body. Am I saying that light travels instantaneously? Well, are we ever without light? That would be a black hole, right?

So what are we talking about here? Light traveling through light? Of course not it travels through space and mediums. But if a black hole is the only place absent of any and all light, I ask u again - light traveling through light?

Quantum mc - All he proved is that it takes longer for the brain to register a source of light emitted from a greater distance. Also notice that there was never a period of time that - that star was dead. Its light shined continuously - all he is talking about is greater light. Visible to the human eye i.e. white light

Zahbudar - Listen to what your saying. Light travels slower in some mediums correct? Take a bullet for example. When if travels into a body its speed decreases and it exists at a lower speed than what it entered. If light travels faster and slower in some mediums that like saying if it traveled through a vaccum, into air, back into a vaccum - its speed will decrease, increase, decrease and increase again. Thats like saying a bullet can travel through a medium (body) speed decrease then exit at a greater speed. Thats properterous. Does light really travel. Or is it what we call lightspeed relative to human perception?

Debobs - How are we to understand light speed. Isn`t speed mass plus momentum or velcoity plus mass or something like that? Light is massless - how can it possibly have a velocity?

Jason T - I think the delay proves nothing. "Information" traveling through "Radio waves" does not mean that radio waves travel at the speed of the information. Its like zenos paradox when talking about motion. Ur brains are filled with beans!

Taelec - It seems like your the only person here that understands that lights mysterious. Sceintists dont have have it pegged yet. Yes, I`am familiar with the double slit experiement. I don`t think that light travels instantenously. I think its always here. But what about when we turn on a lightbulb. I think that the power of the source determines the length of (AB) not the distance from A to B. In other words light does not go from here to there. Earth, Jupiter, etc is in an electromagnetic feild - light is ready to be charged. A light bulb simply charges the electromagnetic field in proportion to it. Power of the source the greaer (AB)

Answer 1

One way to measure the speed of light is to send it along a path of a known distance, at the other end of which is something that will reflect the light back to you. If you know the length of the path (by some independent means), and can measure the time it takes for the light to return, you just divide distance by time to get speed. Many, many experiments of this kind have been done. Look up "Armand Fizeau," who did this experiment as long ago as 1849, by sending a light beam on a return trip of about 8 km, and using an ingenious device that allowed him to measure very tiny time intervals of just a few tens of microseconds.

In modern times, we can do the experiment using much longer time intervals (seconds or minutes), because now we can send light signals (or radio signals, which amount to the same thing) to off-earth targets a known distance away, and wait for them to return. When you send such a signal to the moon, it takes about 2.6 seconds to return. When you send it to Mars, it takes several minutes to return, depending on where Mars is in its orbit.

One interpretation of this result might be: Suppose the light reaches the moon instantaneously and then just "waits" 2.6 seconds before making its (also instantaeous) return trip to the earth? But if that were the case, we would expect the delay always to be 2.6 seconds regardless of how far the light traveled; and we find that this is not the case. (The elapsed time increases or decreases according to the distance.)

Another early calculation was done by Ole Roemer (not Galileo as quantum_mc said). In Roemer's day, the average time between eclipses of Jupiter's moon Io was very precisely known (on account of observing many consecutive eclipses and dividing the total elapsed time by the total number of eclipses). But Roemer observed that the eclipsed occurred several minutes "too late" when Jupiter was far away from the earth; and several minutes "too early" when Jupiter was close. He reasoned that the explanation was that the light from Jupiter (hence, our observation of the eclipse) took a finite time to get from Jupiter to the earth. Since the distance to Jupiter was reasonably well known, it was possible to compare the distance to the time delay and calculate the propagation speed. The answer was in reasonably good agreement with today's value.

Answer 2

Well what you have so far is kind of right. Light acts like a wave a times and like a particle others. Its neither and both at the same time.

Light is a very strange thing indeed. Let me give you an example tha will make some sense
If you know about the slit experiment it will make this a little easier to understand.
Light passing thru a certain slit experiment will cause the light to act like a wave. This will cause ripple patterns. But if you do another experiment on the light and make it act like a particle it will do just that because you make it act like that. But if you leave it along it behaves like a wave again.
So light has the ability to do very strange things
I know I explaind them poorly but the truth is Light will act like a wave and a particle. Will it speed back up once it leaves the medium and enters into a vacum. Yes it will and no it won't If you observe it you mess it up but if you don't observe it it will go back to the same speed. We don't fully understan the quantum nature of light . We have theories that will predict what it does and will do and those are mostly right but then it does things completely baffiling still.
You instant travel idea has some merrit. Two photons millions of light years apart will exibt the same behavior you if at one point they were part of the same light sorce.

I don't fully understand it yet I am working forward so that I do but I do my best to grasp it.

Answer 3

The speed of light can be measured directly usig things beside the eye and brain. Communications between Earth and the Moon during Apollo were subject to a 2.3 second delay, just as you'd expect when communication with something 400,000km away. Communication delays with the Mars rover vary depending on the location of Mars in its orbit. The observation of Jupiter's moon's shows the effects of the speed of light. The speed of light has been objectively verified in literally millions of experiments over hundreds of years.

Your analogy with a bullet is as flawed as any other analogy comparing the quantum with the macroscopic. It just doesn't work that way.

[Edited to add, since you insist on drawing a distinction between information and waves travelling, that laser beams bounced off the reflectors left on the Moon also show the same 2.6 second delay, and there is no information transmitted on those except the light itself.]

Answer 4

Yes.

Light does have a traveling speed from whence it was emanated. That speed is 186,000 Miles per second.

Light may be slowed down somewhat by various mediums,
at which point it is traveling slower, but once slowed down, it does not resume traveling fast again once it possibly exits that medium and enters a vacuum again...it continues at the slower speed. There is nothing in the medium to boost its speed back up as it exits.

No. A bullet does not travel faster when it exits a body. It is in fact slowed down by passing through a body because part of its energy is lost...Same thing happens with protons of light...

Answer 5

Well, the first true measurements of light go back to Galileo.

Galileo discovered the large moons around Jupiter, and plotted when they could be seen. He accurately recorded the orbital periods of Io and Europa.

Well, when Earth was at opposition, and Jupiter was at it's closest, he noted the time that Io appeared from around Jupiter's edge. About 6 months later, when Earth was 186 million miles further, he waited about 1000 more seconds - about 15 minutes - for the event to happen. He figured, based on the additional distance light had to travel, that it's speed was about 186,000 miles a second.

So - this proved light had a definite speed.

Answer 6

Yes. Light speed is finite and measurable. And yes it will accelerate/decelerate through differing media.

But light going from a denser medium to a vacuum is not like a bullet speeding up as it exits a denser medium. Bullets have mass, inertia, and momentum. Light does not.

And there can be places with no light other than black holes. There are no physical constraints to space that preclude that it must contain photons.

Answer 7

Light is indeed an objective measurement and there are various experiments that can confirm it.

Our brains cannot register the speed of light - it appears to be instantaneous to us. In fact, we cannot distinguish anything even remotely as fast.

Light will not accelerate or undergo negative acceleration as it passes through a medium. Its velocity almost instantaneously decreases.

Different wavelengths of light can also have different speeds in different medium. That is why prisms split light up into its spectal colors.

Answer 8

You are wrong.

One can measure the speed of light with an experiment for a couple hundred dollars. Or you just look at Jupiter's moons and use Olaf Roemer's experiment.

If there is a problem with brains here, it is with yours not being trained to think in straight, simple terms. Science requires a certain degree of naive acceptance that the thing you are holding in your hand is the thing you are holding in your hand and not some weird shadow on the walls of a mythical cave.

Try studying physics for a while. It will clear things up.

Answer 9

Light has a speed.... The light of the sun if actually light that was made from a previous time. An example would be a thunderstorm. The light travels first and then the sound of the thunder. Light is fast, but it has a speed.

Answer 10

The velocity of light is a ratio of the diameter of the micromass of the light partilce divide by the period of time it travels during one displacement of Space. Its speed is measured relative to the Earth's frame of reference as approx. 2.997 x10^5 km/sec
The velocity of the micromass of light is dependent on the pressure of the substance of space(thematter medium in which its traveling.)

The equation to calculate the velocity of light is as follows:

Vc^2 = Pressure of space bearing down on the light particle divided by the density of the micromass of light.

Vc^2 =Pr/De ,wher Pr is pressure and De is density. Vc=velocity of light at that particular loaction of space and Time level in the volume of the Universe.

I hope this clarifies some of your conceptions about Light.