Why we cant measure the speed of light

We actually can’t measure the speed of anything, we can only infer it from two position measurements. Each measurement equals zero speed each.

a reply to: dragonridr

Take three prisms, each one configured as a beam splitter divergent at 60 degrees, and use one of them to direct a low-frequency coherent beam to be split into two arms of an equilateral triangle, whose length is as close to half the wavelength of the input beam (I am assuming a laser beam) as is possible. The other two prisims do similarly at the opposite ends of the arms, feeding the light down the third side of the triangle and leaking some un-refracted light out at each corner.

The approximate 1/2 wavelength length can be adjusted so that the oscillations in brightness form a static nodal resonance, indicating with the lenght, the distance each light beam travels in that wavelength, and therefore providing some interferometric precision that matched the light beam's frequency.

As the nodal resonances would be static in three different directions, it verifies that direction is not a factor of the speed of light.

As the wavelength is a function of propagation speed, length, and frequency, one could verify if these are all uniform and that distance, frequency, and other measurables all give a picture consistent with the calculated speed of light.

This would best be done in a vacuum and at a low temperature to remove as many sources of error as possible.

originally posted by: bluemooone2
This is pretty cool. At the 3:30 mark she explains what Einstein said about light very well.

Thanks for finding that. Really cool!

originally posted by: dragonridr

originally posted by: FauxMulder
a reply to: ChaoticOrder

I don't remember anything about an aether. I think the point is no one has ever measured light in one direction. Its next to impossible. The only way I can think of, would be some sort of quantum entangled clocks. Its sort of just a paradox. Kind of like Zeno's paradox.

I'll rewatch the video later and see if he mentioned anything about what you said. Or if I too missed something.

Well yes this could in theory work if quantum entanglement is indeed instantaneous. Then we can have two clocks set to the same time and just take a one way measurement. Problem is we dont know if quantum entanglement is.

I was under the impression quantum entanglement had been proven.

As far-out as the idea seems, quantum entanglement has been proven time and time again over the years. When researchers create two entangled particles and independently measure their properties, they find that the outcome of one measurement influences the observed properties of the other particle.

Link

Scientists have successfully demonstrated quantum entanglement with photos, electrons, molecules of various sizes, and even very small diamonds. The University of Glasgow study is the first ever to capture visual evidence of entanglement, though. The experiment used photons in entangled pairs and measured the phase of the particles — this is known as a Bell entanglement.

The team produced photons with an ultraviolet laser, passing them through a crystal that causes some of the photos to become entangled. A beam splitter turned the beam into two equal “arms” with some of the entangled photos going down different paths. Since they were entangled, they continued to share the same phase even after being separated.

Link

Now, putting that into practical use is a totally different matter.

originally posted by: F4guy
If you know the distance to a mirror, you only need one clock, located at the light emitter source. It can measure the time of transmission and the time of return.

But then this is measuring bi-directionality. They know the average speed of light is 2.99x10^8m/s, but they don't know if it is constant in both directions. It seems silly, but it could actually tell us a lot about the physical world if we can prove the speed in each direction.

a reply to: chr0naut

Using an interferometer you are dealing with at minimum bi directionality of light. We need to measue it in just one direction not 2. We know the average of c when light travels in 2 directions all this would prove is that its constant.

I know people keep thinking this is trivial and who knows it could be. But it also could tell us something about the universe leading to full understanding. If light travels at different speeds we could litterally throw out time dialation from Einstiens theory. We would no longer need to slow time in order for light to maintin a constant speed.

a reply to: cooperton And dragonridr.

There is only one direction from the lights point of reference. Only forwards. Even if fired from an emitter. It travels forward towards the mirror. Then forwards from mirror to emitter.

If this was a multiple choice q and a. I would say the answer is c.

originally posted by: blackcrowe
a reply to: cooperton And dragonridr.

There is only one direction from the lights point of reference. Only forwards. Even if fired from an emitter. It travels forward towards the mirror. Then forwards from mirror to emitter.

When it reflects off an object it could change speed

a reply to: cooperton

It is a constant. It only has one speed. When in a vacuum. Only adding mass will slow its speed.

originally posted by: blackcrowe
a reply to: cooperton

It is a constant. It only has one speed. When in a vacuum. Only adding mass will slow its speed.

Most likely yes, but there is a chance it isn't the same speed in both directions

a reply to: cooperton

Both directions from whose reference frame/position/point of observation?

What direction the observer sees is irrelevant.

It's the lights reference frame that must be considered.

originally posted by: blackcrowe
a reply to: cooperton

It is a constant. It only has one speed. When in a vacuum. Only adding mass will slow its speed.

That is the asumption we have made but we have not proved it to be true. Untill we do it is considered a convention and not fact. And if we are wrong has even wider consequences,

a reply to: dragonridr

You say it's an assumption. You also said earlier " We know the average of c when light travels in 2 directions all this would prove is that its constant".

It's contradictory.

Your 2 directions can be seen as one direction when it is times twice the length.

originally posted by: blackcrowe
a reply to: dragonridr

You say it's an assumption. You also said earlier " We know the average of c when light travels in 2 directions all this would prove is that its constant".

It's contradictory.

Your 2 directions can be seen as one direction when it is times twice the length.

Only if light always moves at the same speed. What if we find its instantanous in one direction for example. Until we can measure light in just one direction we are dealing with an average. This in theory could even explain quantum entanglement we would have no idea where this could lead.

Now having said that i tend to believe light is constant its the simplest solution and I tend to ba a fan of occams razor. But the universe may not care about simplicity.

a reply to: dragonridr

It is measured in one direction if you consider that when fired from emitter/detector to a mirror and back to detector/emitter is a one way forward only action as far as the light is concerned. You may say it is twice the length from emitter to mirror to calculate your irrelevant directions.

I'm out of this now. I hope a member with qualifications in the subject will put us all out of this misery.

originally posted by: blackcrowe
a reply to: dragonridr

It is measured in one direction if you consider that when fired from emitter/detector to a mirror and back to detector/emitter is a one way forward only action as far as the light is concerned. You may say it is twice the length from emitter to mirror to calculate your irrelevant directions.

I'm out of this now. I hope a member with qualifications in the subject will put us all out of this misery.

I suggest you take the time to read the entire thread. Or even watch the video posted This argument has been made by scientists since 1905 when Einsine proposed the theory. As far as qualifications that doesnt change the fact this has never been confirmed as of yet through experimentation. I understand this can bake peoples noodle so to speak but as we have learned the universe is a very strange place.

a reply to: dragonridr

OK.

I have read all the thread. But you have reverted back to directions which are irrelevant as you was doing on page one where i replied.

I will take it further for you to show what happens in 2 real directions.

Above my first reply on page one. Mobius made a valid reply. Based on his left and right comment we will see what the result is.

We emit light from a point we can observe its behaviour from in 3d. And, we want to measure the speed it takes to reach a detector to our right.

How is that not possible?

But. Is it the same speed measuring to a detector to the left?

What you have to consider here is that right and left are aspects of the width dimension.

If you take your measurement of the right. Call it c. Rotate the width dimension 90 deg x 90 deg = 180 deg. Not only have you found left. But it is also c^2 to right which measured c. c = c^2

You could call left c. Right would become c^2

You can now complete the other two dimensions yourself. And see light is constant in all observed directions. But the light you observe is only ever travelling forwards from its reference point/position.

If you need further help. Look into quaternions. But consider the ijk used is actually i = length, j = height and k = width.

originally posted by: dragonridr

originally posted by: Akragon
a reply to: dragonridr

Wouldn't a laser be able to measure light traveling in one direction?

No again you need 2 clocks you have to measure when it left and when it arrived at its destination. Relativity tells us the difficulty in syncing two clocks. This is why they used a mirror and only one clock to calculate c. If light is effected by directionality no matter how we try to figure out the speed of C will always use 2 directions. Lets say we use your laser and a camera. And we see how long it took light to cgo through a vacuume. The problem is we have to take in to account the time the light took to reach the camera. Meaning we are still measuring it in two directions.

You can theoretically check the one way speed of light using a black hole. Shoot a beam of light towards a black hole along a geodesic that curves the beam back to your detector.

a reply to: blackcrowe

Please do us all a favor and watch the video.


You continue to talk about something without understanding the problem.

In a previous life I spent a lot of time with video forensics. I was tasked with measuring the speed of objects in videos with zero reference of size and or distance. While doing so I invented some techniques that helped me measure the speed of objects using their own size. Even if I didn't know the actual size in real life I could measure it in arbitrary units, then make assumptions on what the object is so I could then approximate the speed.

For example, I could measure the object had moved its own length multiplied by 5 in 1 second of video (which ran at 30 FPS).

Once I have that measurement I can then plug in some values. For example, if the object was a Boeing 747-8 which is 250 feet long, and it traveled its own length multiplied by 5, that means the object was moving 1,250 feet per second. That is 852 MPH. Since a 747-8 has a top speed of 614 MPH I could then assume the object is not a Boeing 747-8.

When measuring the speed of an object most people think you need at least 2 points. I found that is wrong. You actually need 3 points. A start point (1), an end point (2), and the object's position point (3). I don't know why everyone ignores the position point.

I also found that you can invert the 3 points. You can have a single point of reference (1), and then you can measure when the object first intersects with that point (2), and when the object stops intersecting with that point (3). Then, if you knew the object's length you could calculate the speed it traveled through that initial reference point.

Put simply, if you go back to ignoring the position point of the object, you only need 1 point of reference to measure the speed of an object (if you know the object's length).

Now you just have to all agree on what the size of a photon is. Or should I say the size of a light quantum / energy packet.