Does anyone know what the fastest-moving speed of light test on earth was? Or how fast?

I.e. if someone put a flashlight on a race car that was doing 300mph, and tested the speed of light from the headlights, would they record the speed as 'SOL - 300mph' ?

If so, what is the largest speed that has ever been recorded accurately and subtracted? Or am I misunderstanding the speed of light?

https://en.wikipedia.org/wiki/Michel...ley_experiment

detailed analysis here ch2
https://www.pdfdrive.com/special-rel...189778100.html

https://en.wikipedia.org/wiki/Velocity-addition_formula

You would observe c no matter how fast you or they are moving. It is a principle of relativity.

If they are moving c/4 speed, and they shoot an object at you, and you calculate that objects speed to be c, then 3c/4 would be the speed that object was shot at you.

I'm wondering what's the biggest that number has been (the c/4 speed) in a test that actually measured c on the other end.

I'm assuming someone currently holds the record for the largest c/4 speed mentioned above. I'd like to find out what that number is and read about the test that made it. I'll start reading your links now, thanks masq.

How fast do you think the earth and the milky way are moving through the universe? Just relative to our our own galaxy we are moving at over 500,000 mph. Light hitting us from other galaxies still measure velocity C.

I have no idea how fast things are moving that are billions ^ billions miles away, and even if I did, my confidence in my knowledge would be inversely proportional to how far away the object in question is.

But to give you a better response: how fast things are moving in the universe is not controllable but a race car's speed is. I believe it is preferred to be able to control as many constants and/or variables as you can when doing experiments.

edit: Would this experiment be deemed as a waste of time and therefore it has never been done? Or has it never been done because we don't have the technology to do it yet?

Yes these tests have been done many times, and every observation confirms that C always measures the same regardless of POV or relative motion. Look up Michelsen Morely experiments. There are various theories which attempt to explain this phenomenon.

You need to define the reference frames (ie speed relative to what reference frame), for the question to fully make sense when you’re talking about speeds close to c. One of the things with relativity is that there is no such thing as absolute speed.

I don’t know the answer to this but I think they’ve used celestial bodies with this type of experiment so things that are moving way faster relative to an Earth observer than anything on Earth. Not sure what that number is though.

We have tried to do experimental and observational tests of just about everything. We've done experiments trying to determine stuff like the weight of a soul. It would be weird if we decided to skip over trying to check whether the speed of light is a constant because THAT would be more of a waste of time. Like super weird.

Actually, measuring the speed of light is a waste of time, or more precisely, it isn’t really possible. Any measurement of the speed of light is really just a distance measurement. That’s because our unit of distance, the meter, is officially defined as the distance light travels in a certain fraction of a second (approximately 1/300,000,000 seconds; there is a more exact number in the official definition but I can’t recall it and I’m too lazy to look it up).

If you try to measure the speed of light, you must perform a time and a distance measurement, with the speed being the ratio of distance to time. However, there is no way to measure a distance that makes this ratio anything other than c. The distance travelled by light in time t is given by definition as d=ct. Therefore the measured speed is ct/t = c no matter how the measurement is carried out. The definition of the meter effectively defines the speed of light.

You are mistaken in your formula for composition of velocity. Velocities are NOT additive, so a person moving at c/4 and shooting an object at speed 3c/4 in his reference frame would not give c for the object speed in your reference frame. If you are composing two velocities u and v, the correct formula is not u+v as is naively supposed, but rather (u+v)/(1+uv/c^2). Plugging c/4 and 3c/4 into that formula gives (c/4+3c/4)/(1+3c^2/16c^2) = c/(1+3/16) = 16c/19, not c.

Importantly, there are two things to note about this formula. First if u and v both are less than c, then the result of this formula is likewise less than c. Second, if u=c then the formula gives (c+v)/(1+cv/c^2) = (c+v)/(1+v/c). Multiply both the numerator and denominator of that expression by c and you get c(c+v)/(c+v) = c. Thus, if one velocity equals c, the composed velocity .also is c. Therefore if someone travels toward you at c/2 and shines a light at you, you measure the speed of that light as c. IOW, the speed of light is a constant regardless of the motion of either the source or detector.

This seems counterintuitive only because we don’t experience high speeds. Even the fastest military aircraft don’t move anywhere close to c. Velocities really are additive, or at least close enough that we can’t measure any deviation from additive type. Try for example u=v=c/100000. That gives 2c/100000 divided by the number 1+ 10^-10, which is very close to u+v.

I assumed in my OP the tests had been done but I was wondering what the top speed tested has been. I thought there might be some sort of current top speed tested record. Something how they do with the land speed records on the salt flats.

Do you think you could you re-word this sentence before I try to nit pick it? I'm not sure if you are in the mood to get philosophical or not...

Sometimes the super weird is super standard. I have no idea if the above quoted is true, but if it is,

I'm not trying to be a drag here but that sounds a bit circular to me... and unfalsifiable.

If I stand still and person A is 10meter away from me and person B is 20m away. A throws a ball at me with speed s. B runs at speed bs up to the 10 meter line, then throws the ball at speed s. Wouldn't B's ball hurt more? I assumed it would hurt bs more.

It woulg be a bit wierd to check as we know it isn't

c is a constant

</nit>

We don't check what we know anymore in science?

You were implying you were checking it was true. It isn't.

Nature abhors a vacuum, Brian.

PairTheBoard

It's my understanding that C is constant. Just that with the absence of a vacuum, a photon is being absorbed, re-emitted, absorbed, emitted etcetera to appear as if it's traveling a bit slower. It's moving through a non vacuum like those steal balls on strings where you pull one and the opposite ball pops up. But the photons themselves are traveling at precisely c and only c from the moment of their birth to the moment of absorbtion without any acceleration or deceleration.

Not at all circular. The second, our standard time unit, is defined by the frequency of light emitted by a given electronic transition in cesium atoms. The details are not really important. What is important is that we have a definition of the second. At one time we likewise had a definition of the meter independent of the speed of light. When that was the case, experimental determination of light speed made sense. However, measurements of light speed got to be very precise, so much so that the limiting factor in the precision of the measurement was actually the uncertainty in reproduction off the standard meter. Therefore it made sense to DEFINE the meter based on measurement of light speed rather than another way.

Previously the meter was defined by a metal bar with two marks kept under very carefully controlled conditions. That was quite imprecise since temperature fluctuations could change the length slightly. To give better precision, the wavelength of certain light was used, but the measurement of this wavelength relied upon experimental determination of c. Once that determination became more precise c was used to define the length standard, effectively setting the value of c by definition.

The meter is now defined as the distance travelled by light in a vacuum during a time of 1/300,000,000 seconds (that is approximate; the actual denominator is.slightly lower). We can measure this time period independently. If we watch our light travel for this time, we previously could use our independently defined meter as a standard to measure the distance and therefore c. Now we know the distance without measurement- it’s exactly 1 meter by definition. Nothing circular about it. We just set the denominator in the definition of the meter so that we didn’t have to change our meter sticks - the new definition gives the same length as the old ones.


https://www.nist.gov/pml/weights-and...i-units-length

The reasoning there is still confusing.

First it is simply "agreed" that the speed of light will be 299,792,458 meters per second. This is not measured, it is just agreed to as the standard by international consensus.

Then from that, we derive the length of a meter as the distance traveled by light in 1/299,792,458 seconds.

The only thing that makes it not circular is that C is not based on a measurement at all, but just on an agreed constant value. Without measurement, how is this assumed? With measurement, the definition becomes circular. The official explanation seems to get around this by making it clear it is not a measured value.

The two definitions absolutely depend on each other and neither can exist without the other. They are jointly defined to be in agreement, and neither one is independently defined.

My understanding of stremba's explanation. The speed of light was first measured to be 299,792,458 meters/sec using the old "fixed" measuring stick for the meter. However, this could only be considered an approximation for c since the "fixed" measuring stick actually varied due to inability to maintain absolutely precise control conditions for it. So in order to fix this imprecision they decided to pin down an exact relationship between the meter and the speed of light by redefining the meter in terms of the "constant" speed of light. Of course this project fails if it turns out that c is not constant after all. In that case the meter is still not "fixed".

I understand the University of Q is coming out with a "Lazy Photon" theory in which some photons may lollygag.


PairTheBoard