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Old 31st October 2020, 06:05 AM   #1
Steve001
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Why no one has measured the speed of light.

A YouTube video by Veritasium. I suspect like everybody else took it as a given that it has been measured.
https://youtu.be/pTn6Ewhb27k
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Old 31st October 2020, 06:21 AM   #2
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For those of us not interested in sitting through YouTube videos, could you please summarise the key points made?

Dave
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Old 31st October 2020, 06:26 AM   #3
Steve001
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Originally Posted by Dave Rogers View Post
For those of us not interested in sitting through YouTube videos, could you please summarise the key points made?

Dave
Click the link to read the description. This is not a crank vid I assure you.
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Old 31st October 2020, 06:47 AM   #4
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Description makes it sound like a crank vid to me.
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Old 31st October 2020, 06:55 AM   #5
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The main point is that there's no way to measure the one-way speed of light. All methods rely on a two-way method assuming isotropy.
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Old 31st October 2020, 07:03 AM   #6
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So it's clickbait crap.
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Old 31st October 2020, 07:16 AM   #7
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Old 31st October 2020, 07:20 AM   #8
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Originally Posted by theprestige View Post
So it's clickbait crap.
It's not clickbait crap. Have ever watched this channel? Apparently the answer is not.
This vid goes into depth why the one way speed of light has never been measured. Did you know it has not? I didn't. It's more complicated than I ever considered.

Last edited by Steve001; 31st October 2020 at 07:31 AM.
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Old 31st October 2020, 07:33 AM   #9
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Originally Posted by Steve001 View Post
It's not clickbait crap. Have ever watched this channel? Apparently the answer is not. It's goes into depth why the one way speed of light has never been measured.
And the implications of this are?
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Old 31st October 2020, 07:33 AM   #10
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"Measuring the speed of light requires a two way setup and certain well supported assumptions" is not the same as "the speed of light has never been measured".

The former is an interesting dive into the scientific details. The latter is telling you you're wrong when you're actually right, to get views.
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Old 31st October 2020, 07:35 AM   #11
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Originally Posted by zooterkin View Post
And the implications of this are?
Watch the vid then talk. But there are none.
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Old 31st October 2020, 07:49 AM   #12
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Originally Posted by Steve001 View Post
It's not clickbait crap. Have ever watched this channel? Apparently the answer is not.
This vid goes into depth why the one way speed of light has never been measured. Did you know it has not? I didn't. It's more complicated than I ever considered.
Actually, it's clickbait crap.

Well, that's slightly unfair, and I only skimmed through the video so I may have missed some things. If their point is to described how difficult certain things are to measure, and the non-intuitive nature of how things have to be done when measuring such, then great. It's fine.

If their point is that there is some sort of fundamental knowledge that we really don't have, and that the universe may work differently than we think it does, because an observer on Mars cannot tell the difference between a uniform speed, versus a one way speed that is different in different directions, then it's hogwash. When clicking random points, the video made a great deal about the idea that our assumptions were all based on something Einstein said in 1905, which is hogwash.

The speed of light is more than just some way of measuring how much time elapses between sending and receiving messages or, more generally, between the time an event happens to the time it is observed. It's a fundamental constant of the universe. It is equal to 1/sqrt(mu*epsilon), where mu and epsilon are the electric and magnetic permeability of free space. It is the factor that one can apply to mass increases as particles get close to that speed. In one of the brief clicks I made into the video, the narrator said that no laws of physics would be violated if the speed was different in each direction, but then he didn't go into any laws of physics. He just talked about measuring time passage between events.

In reality, a whole heck of a lot of laws of physics would be busted if the speed of light was not uniform in every direction.

So, it's kind of a cool video, but I didn't really get its point. We really do know the speed of light. It really has been measured, although you can't measure it exactly the same way you would measure things that go much slower than the speed of light. If that was their point, then fine. If, on the other hand, they were suggesting that there really is some unknown thing about light that we have never confirmed, but just assumed, it's wrong.
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Old 31st October 2020, 07:51 AM   #13
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Originally Posted by Steve001 View Post
It's not clickbait crap. Have ever watched this channel? Apparently the answer is not.
This vid goes into depth why the one way speed of light has never been measured. Did you know it has not? I didn't. It's more complicated than I ever considered.
But it's not more complicated than a lot of other people have considered, including the people who measure the speed of light.
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Old 31st October 2020, 07:54 AM   #14
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Originally Posted by Steve001 View Post
Watch the vid then talk.
Um, no.

This is a text-based medium. If you want to discuss a topic about physics, please put it into words. I (and I suspect many others) donít have time to waste on watching YouTube videos when the meat of the idea can be conveyed much quicker via the written word.
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Old 31st October 2020, 08:02 AM   #15
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Originally Posted by theprestige View Post
"Measuring the speed of light requires a two way setup and certain well supported assumptions" is not the same as "the speed of light has never been measured".

The former is an interesting dive into the scientific details. The latter is telling you you're wrong when you're actually right, to get views.
Certainly the title is meant to pique curiosity, but to equate it with click bait trash is a gross unwarranted presumption on your part since you've not watched the vid to see why the one way speed of light has not been experimentally measured. Even Einstein recognised this convention we all assume in his 1905 paper " On The Electrodynamics of Moving Bodies" Perhaps you can find a solution to experimentally proving the one way speed of light is the same in all directions.
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Old 31st October 2020, 08:06 AM   #16
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Originally Posted by Steve001 View Post
Watch the vid then talk. But there are none.
Watch the vid! #6 will blow your mind about

<script>
<options>
<list = "weight loss","retirement","solar panels","sex drive","insurance">
<end list>
<end options>
<end script>





This is what I think when people ask me to watch a video without any explanation and then give the same type of answer when asked about why I should watch the same video or who can't sum up key parts.
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Old 31st October 2020, 08:08 AM   #17
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Originally Posted by Steve001 View Post
Certainly the title is meant to pique curiosity
When the reason curiosity is piqued is because the title is misleading or downright incorrect, thatís pretty much the definition of click bait.
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Old 31st October 2020, 08:10 AM   #18
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In particular, if we couldn't actually tell that the speed of light is the same in every direction, we wouldn't have ended up with relativity. The speed of light being faster in one direction than on the way back is NOT something that nobody ever considered. It being different in different directions was in fact the original assumption, when we assumed that there's some kind of ether or at least preferred frame of reference.

I mean, think about it. Whether it's speed of sound or waves on the water, it has a preferred frame (the air or respectively the water), and if you move in relation to that frame, you measure a different speed. If you're looking at, say, the wave on the ocean created by the wake of a ship (so it's the same kind of propagating information about an event), the speed you see from the shore (which is not moving in relation to the water) is very different from the speed you see from a fast boat moving towards the wave, which in turn is very different from the speed you see from a fast boat moving away from the wave.

That's the NORMAL behaviour we expect from any wave in a medium, or really any kind of movement before we knew about relativity. The medium is the preferred frame, and an observer moving relative to that preferred frame sees different speeds in different directions.

It's for example what you'd see with sonar/ASDIC. If you're in a destroyer moving at, say, 40 knots, and you're pinging a submarine in front of you, the speed of your ping relative to you is slower when moving towards the sub and faster on the way back. Because it's constant relative to the water, but you're moving relative to the water, so your own speed is getting added or respectively subtracted.

Far from being something nobody thought about, it's how we EXPECTED light to behave too. We EXPECTED that, since we move in space, relative to US we'd see light moving faster in one direction than in the other.

The big surprise was basically that we disproved that.

So basically TL;DR version: I'm not sure it's even click-bait. It seems more like a roundabout version of the usual relativity-denialist idiocy.
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Old 31st October 2020, 08:13 AM   #19
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Originally Posted by zooterkin View Post
This is a text-based medium. If you want to discuss a topic about physics, please put it into words. I (and I suspect many others) don’t have time to waste on watching YouTube videos when the meat of the idea can be conveyed much quicker via the written word.
It's always a good idea to model the required behaviour. In this case, a good approach would have been: "While the title is something of an overstatement, this video discusses the fact that the anisotropy of the speed of light, which would have serious implications for our current understanding of physics if non-zero, has not been and arguably cannot be measured." That would give us all a better idea of what the subject of the thread actually is.

Dave
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Old 31st October 2020, 08:20 AM   #20
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Originally Posted by zooterkin View Post
Um, no.

This is a text-based medium. If you want to discuss a topic about physics, please put it into words. I (and I suspect many others) donít have time to waste on watching YouTube videos when the meat of the idea can be conveyed much quicker via the written word.
But members have time to waste opining. Like you did writing that reply. Frankly, I posted this vid not to start a flame war but merely as a huh I never considered that. So if your'e going to waste time why not watch an interesting physics vid. There's little to talk about beyond that. It's not woo woo. It's not controversial. It does not change how physics works. But it is a huh moment.
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Old 31st October 2020, 08:30 AM   #21
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Click bait title aside, it seems the point of the video is that there exists no mechanism, or even thought experiment, that can determine whether the speed of light is directional. While that may seem bizarre, it actually fits with our understanding of relativity.

My view is that it's a meaningless question because whether or not the speed of light is isotropic affects absolutely nothing. It just seems like it should at first glance.

Interesting that it has captured the imagination of so many over the years. Quite a number of papers on it.

This is a comment letter referring to the 2009 paper in Am. J. Phys. they mention in the video.

https://aapt.scitation.org/doi/10.1119/1.3364868
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Old 31st October 2020, 08:32 AM   #22
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Originally Posted by Steve001 View Post
Certainly the title is meant to pique curiosity, but to equate it with click bait trash is a gross unwarranted presumption on your part since you've not watched the vid to see why the one way speed of light has not been experimentally measured. Even Einstein recognised this convention we all assume in his 1905 paper " On The Electrodynamics of Moving Bodies" Perhaps you can find a solution to experimentally proving the one way speed of light is the same in all directions.
And this is why the vid is kind of misleading click-bait. Experimenters are well aware of this problem, and they found solutions a long time ago.

When James Clerk Maxwell wrote his four equations describing electromagnetism, one prediction of those equations was that there ought to be travelling electromagnetic waves, and the speed of those waves could even be predicted based on those equations. Those waves were not observed in a laboratory, but their existence was predicted.

Later, someone measured the speed of light, using the two way method, and said, "Whoa. That's the speed that was predicted in Maxwell's equations." That was how we found out that light was electromagnetic.

Maxwell's equations aren't directional. They aren't about one way or two way light travelling. They aren't about light at all. (At least, he didn't know they were about light when he wrote them.) They're about electromagnetism.

The video talks about sending and receiving signals. Well, those signals are sent and received using devices that manipulate or detect oscillating magnetic and electric fields. They only work because they can be tuned based on electromagnetic field strength. If light somehow behaved differently when travelling in different directions, the transmitters and receivers would have to take that into account. But they don't. The receiver on Mars works the same as the receiver on Earth. That would not be the case if the light was travelling at different speeds.

So, for all the reasons that the video discusses, it is impossible to measure what they call the one way speed of light directly, as a distance/time style measurement. However, there isn't any doubt about whether the two way speed measurements are somehow suspect. The experimental proof that they are perfectly sound is found in the fact that the receivers and senders work identically regardless of direction.

(More generally, the universe would break. Those electromagnetic properties that give rise to travelling radio waves also describe a lot about the way atoms hold together.)
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Old 31st October 2020, 08:34 AM   #23
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Originally Posted by Dave Rogers View Post
It's always a good idea to model the required behaviour. In this case, a good approach would have been: "While the title is something of an overstatement, this video discusses the fact that the anisotropy of the speed of light, which would have serious implications for our current understanding of physics if non-zero, has not been and arguably cannot be measured." That would give us all a better idea of what the subject of the thread actually is.

Dave
Nicely put.
The title is meant to pique curiosity and disbelieve.
The subject of the vid limits itself to why measuring the one way speed of light has not been experimentally achieve.
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Old 31st October 2020, 08:44 AM   #24
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Originally Posted by Meadmaker View Post
And this is why the vid is kind of misleading click-bait. Experimenters are well aware of this problem, and they found solutions a long time ago.

When James Clerk Maxwell wrote his four equations describing electromagnetism, one prediction of those equations was that there ought to be travelling electromagnetic waves, and the speed of those waves could even be predicted based on those equations. Those waves were not observed in a laboratory, but their existence was predicted.

Later, someone measured the speed of light, using the two way method, and said, "Whoa. That's the speed that was predicted in Maxwell's equations." That was how we found out that light was electromagnetic.

Maxwell's equations aren't directional. They aren't about one way or two way light travelling. They aren't about light at all. (At least, he didn't know they were about light when he wrote them.) They're about electromagnetism.

The video talks about sending and receiving signals. Well, those signals are sent and received using devices that manipulate or detect oscillating magnetic and electric fields. They only work because they can be tuned based on electromagnetic field strength. If light somehow behaved differently when travelling in different directions, the transmitters and receivers would have to take that into account. But they don't. The receiver on Mars works the same as the receiver on Earth. That would not be the case if the light was travelling at different speeds.

So, for all the reasons that the video discusses, it is impossible to measure what they call the one way speed of light directly, as a distance/time style measurement. However, there isn't any doubt about whether the two way speed measurements are somehow suspect. The experimental proof that they are perfectly sound is found in the fact that the receivers and senders work identically regardless of direction.

(More generally, the universe would break. Those electromagnetic properties that give rise to travelling radio waves also describe a lot about the way atoms hold together.)
I have no doubt the speed of light is what has been measured to be. I just never considered the one way speed of light measurement difficulty.
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Old 31st October 2020, 09:14 AM   #25
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Originally Posted by Steve001 View Post
I have no doubt the speed of light is what has been measured to be. I just never considered the one way speed of light measurement difficulty.
And that aspect of the video is pretty cool. It demonstrates why light speed can't be measured the way one might intuitively think that speeds ought to be measured. That's neat.

And if the click-baity style of drawing you in to make people see that works, it's not so bad.

It seemed to me, though, that the video makers were trying to suggest that there really was some sort of uncertainty about whether scientists had really gotten it right. It seemed like they were saying that somehow there was a deficiency in how this subject was being approached, and that it all rested on some obscure reference by Einstein in 1905 that no one had ever challenged. That's not true. It's a well understood problem, and researchers are well aware of it, and there have been plenty of experiments that demonstrate that there's no issue.
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Old 31st October 2020, 09:36 AM   #26
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Originally Posted by sphenisc View Post
The main point is that there's no way to measure the one-way speed of light. All methods rely on a two-way method assuming isotropy.
Except I don't think even that is totally true.

GPS signals depend on the speed of light for positioning. The signal travels from the GPS satellite to the receiver on a one-way trip. GPS turns the speed of light into a distance to find your position, but the other way around actually works as well: if you know where you are, then you know how fast the light traveled. The fact that GPS positioning is accurate tells us that the assumed speed of light was accurate, but I bet you could use GPS data to derive a measurement of the speed of light. Everything is there already.
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Old 31st October 2020, 10:12 AM   #27
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Originally Posted by Dave Rogers View Post
It's always a good idea to model the required behaviour. In this case, a good approach would have been: "While the title is something of an overstatement, this video discusses the fact that the anisotropy of the speed of light, which would have serious implications for our current understanding of physics if non-zero, has not been and arguably cannot be measured." That would give us all a better idea of what the subject of the thread actually is.

Dave
Wouldn't I have to watch the video first, in order to be able to do that?
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Old 31st October 2020, 10:15 AM   #28
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Originally Posted by Steve001 View Post
But members have time to waste opining. Like you did writing that reply. Frankly, I posted this vid not to start a flame war but merely as a huh I never considered that. So if your'e going to waste time why not watch an interesting physics vid. There's little to talk about beyond that. It's not woo woo. It's not controversial. It does not change how physics works. But it is a huh moment.
It's not just time. I'm browsing the forum whilst usually having some form of video or audio entertainment on in the same room. I have the sound turned off on the device I'm reading the forum on. Watching a video would entail stopping or muting what I'm listening to, turning on the sound on the device I'm on, then reversing the process when I'm finished. In addition, I'm often not alone, and doing the foregoing would disturb the other person in the room.

Maybe the people who post links to videos with no explanation have simply not considered this, and pointing it out to them may cause them to alter their behaviour in future. In which case, sharing my thoughts is not a waste of time. I live in hope.

ETA: And I've spent considerably less time on this thread than the 20 minutes or so it would take to watch the video. You're the one who thinks the members here have nothing better to do that watching a 20 minute video purely on your say-so. When they take less time than that to object, you have the nerve to berate them?
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Old 31st October 2020, 10:21 AM   #29
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Originally Posted by Steve001 View Post
Certainly the title is meant to pique curiosity, but to equate it with click bait trash is a gross unwarranted presumption
Lying to pique curiosity totally warrants the equation to clickbait trash. The speed of light has been measured.

https://xkcd.com/169/

Quote:
on your part since you've not watched the vid to see why the one way speed of light has not been experimentally measured.
And this is the lie. You're equivocating between "the speed of light has not been measured" and "the one way speed of light has not been measured". Why are you lying to pique interest anyway? It's condescending and totally unnecessary.
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Old 31st October 2020, 10:23 AM   #30
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Originally Posted by Steve001 View Post
But members have time to waste opining. Like you did writing that reply. Frankly, I posted this vid not to start a flame war but merely as a huh I never considered that.
You never considered that no one has measured the speed of light? Huh. I wonder why.

ETA: Time spent opposing the normalization of clickbait - especially in STEM articles - is not wasted at all. You have time to waste posting clickbait and defending the practice; don't complain about the responses.

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Old 31st October 2020, 10:25 AM   #31
HansMustermann
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Originally Posted by Ziggurat View Post
Except I don't think even that is totally true.

GPS signals depend on the speed of light for positioning. The signal travels from the GPS satellite to the receiver on a one-way trip. GPS turns the speed of light into a distance to find your position, but the other way around actually works as well: if you know where you are, then you know how fast the light traveled. The fact that GPS positioning is accurate tells us that the assumed speed of light was accurate, but I bet you could use GPS data to derive a measurement of the speed of light. Everything is there already.
While that is true, I don't think you even need to go that far to show that yes, the speed of light is constant even on one-way trips. You just need to do the two slit experiment, and put the whole thing on a carousel and slowly rotate it around. The distribution of phase across distance is a function of wavelength, which is frequency times speed of light. So basically given the same frequency, if speed of light were different in different directions, wavelength would change as you turn that thing around, so the interference bands would change.

Now one could object that it still involves the way back to your eyes, but that doesn't affect the interference bands on the screen in any way. Since, you know, it happens AFTER those photons hit the screen in that particular pattern. Forming the interference bands is strictly a one-way affair: the way from the lightbulb to the screen.

So there we go. Far from being something that stumps physicists, it's something one can prove in a school science class without any special equipment. If you have drapes (to make the room dark), a flashlight, a coloured filter cap for it, two pieces of cardboard, and something you can turn around (one of those tables on wheels or even a tray you can rotate around on the table), you're all set to prove that yes, the speed of light doesn't change with direction.

I.e., the claim in the title isn't just wrong, it's TRIVIALLY wrong.
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Old 31st October 2020, 10:32 AM   #32
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Originally Posted by Meadmaker View Post
And that aspect of the video is pretty cool. It demonstrates why light speed can't be measured the way one might intuitively think that speeds ought to be measured. That's neat.

And if the click-baity style of drawing you in to make people see that works, it's not so bad.
It's still pretty bad. It's dishonest. It's manipulative. It's condescending. And there's going to be some percentage of people who are only going to get as far as the headline, and come away thinking no one has measured the speed of light. I can't think of any good reason to put that idea out there at all. Certainly not just to drive clicks to your YouTube channel. Popular science deserves better than that.
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Old 31st October 2020, 10:35 AM   #33
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The one-way speed of light can not be measured, only the two-way speed of light can, none of this is new. This isn't all too difficult to understand either by taking minkowski space and noting that the one-way speed of light corresponds to the choice of basis. In particular, if the time basis vector is orthogonal to the space basis vectors then the one-way speed is c in all directions, whereas if the time basis vector is angled towards some direction wrt the space basis vectors then the one-way is anisotropic along that direction with the amount of deviation from isotropy corresponding to the angle of the time basis vector.

All physical calculations still work out the same just like if you had an orthogonal basis. It's convention to use an orthonormal basis, and the Lorentz transformations take their simplest form in such a basis, but there's nothing stopping you from using a non-orthogonal basis and deriving the Lorentz transformation in that basis instead, which is when you'll encounter anisotropic light speed. Ultimately the (an)isotropy of the speed of light is just a coordinate artifact, people just seem to generally assume that the speed of light is isotropic because the conventional form of the Lorentz transformation is derived in an orthonormal basis where light speed happens to be isotropic.
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Old 31st October 2020, 10:43 AM   #34
Meadmaker
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Originally Posted by theprestige View Post
It's still pretty bad. It's dishonest. It's manipulative. It's condescending. And there's going to be some percentage of people who are only going to get as far as the headline, and come away thinking no one has measured the speed of light. I can't think of any good reason to put that idea out there at all. Certainly not just to drive clicks to your YouTube channel. Popular science deserves better than that.
Fair enough observations.
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Old 31st October 2020, 10:58 AM   #35
Steve001
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Originally Posted by theprestige View Post
You never considered that no one has measured the speed of light? Huh. I wonder why.

ETA:
Time spent opposing the normalization of clickbait - especially in STEM articles - is not wasted at all. You have time to waste posting clickbait and defending the practice; don't compl7ain about the responses
.
You are right that I never have considered if the one way speed of light has been measured when I thought that it had been. Have you watched this vid? A response to the blue text. You seemingly want to always argue just for your own pleasure which is fine, but at least argue over something worthy

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Old 31st October 2020, 11:08 AM   #36
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Originally Posted by Steve001 View Post
A YouTube video by Veritasium. I suspect like everybody else took it as a given that it has been measured.
https://youtu.be/pTn6Ewhb27k
I'm on it. I've ordered a 300,000 km ruler from Amazon, and a rocket ship to send somebody to the other end of it to observe. I already have a flashlight. I'll let you know the results.
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Old 31st October 2020, 11:20 AM   #37
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As usual, the usual suspects judge a video, without even bothering to watch it.

Veritasium is a channel I subscribe to, Its an excellent channel, and, at least for people for whose attention span goes beyond a five second sound bite, two lines of text on a forum and 140 Characters on a twitter post or are too ******* lazy to spend a few minutes being informed, they are well worth watching.

Originally Posted by Steve001 View Post
Have you watched this vid? A response to the red text. You seemingly want to always argue just for your own pleasure which is fine, but at least argue over something worthy
THIS!!!
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Old 31st October 2020, 11:23 AM   #38
theprestige
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Originally Posted by Steve001 View Post
You are right that I never have considered if the one way speed of light has been measured when I thought that it had been. Have you watched this vid? A response to the red text. You seemingly want to always argue just for your own pleasure which is fine, but at least argue over something worthy
Your clickbait headline doesn't mention the one way speed of light at all. The content of the video doesn't match the claim of the clickbait headline. You keep equivocating between the two, to try to make it look like your clickbait headline is is actually a reasonable and honest title.

And again, pushing back on dishonest clickbait in STEM subjects is a worthy thing to argue over.

I never disputed that the video talks about measuring the one-way speed of light. I grant that it's a worthy subject, and people not familiar with it may get a lot out of watching the video.

But the headline lies about what's in the video. Lies unnecessarily. It's weird that you're defending this practice. It's also weird that you would think that me watching the video would somehow change my mind about the headline. Unless me watching the video retroactively inserts the phrase "one way" into the headline?
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Old 31st October 2020, 11:31 AM   #39
Steve001
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Originally Posted by theprestige View Post
Your clickbait headline doesn't mention the one way speed of light at all. The content of the video doesn't match the claim of the clickbait headline. You keep equivocating between the two, to try to make it look like your clickbait headline is is actually a reasonable and honest title.

And again, pushing back on dishonest clickbait in STEM subjects is a worthy thing to argue over.

I never disputed that the video talks about measuring the one-way speed of light. I grant that it's a worthy subject, and people not familiar with it may get a lot out of watching the video.

But the headline lies about what's in the video. Lies unnecessarily. It's weird that you're defending this practice. It's also weird that you would think that me watching the video would somehow change my mind about the headline. Unless me watching the video retroactively inserts the phrase "one way" into the headline?
That is the title of the vid. Obviously this bothers you greatly, so I suggest you take your grievance to Veritasium. Btw, has anyone brought it to your attention how cantankerous you are.

Last edited by Steve001; 31st October 2020 at 11:34 AM.
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Old 31st October 2020, 11:40 AM   #40
Steve001
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Originally Posted by Meadmaker View Post
Actually, it's clickbait crap.

Well, that's slightly unfair, and I only skimmed through the video so I may have missed some things. If their point is to described how difficult certain things are to measure, and the non-intuitive nature of how things have to be done when measuring such, then great. It's fine.

If their point is that there is some sort of fundamental knowledge that we really don't have, and that the universe may work differently than we think it does, because an observer on Mars cannot tell the difference between a uniform speed, versus a one way speed that is different in different directions, then it's hogwash. When clicking random points, the video made a great deal about the idea that our assumptions were all based on something Einstein said in 1905, which is hogwash.

The speed of light is more than just some way of measuring how much time elapses between sending and receiving messages or, more generally, between the time an event happens to the time it is observed. It's a fundamental constant of the universe. It is equal to 1/sqrt(mu*epsilon), where mu and epsilon are the electric and magnetic permeability of free space. It is the factor that one can apply to mass increases as particles get close to that speed. In one of the brief clicks I made into the video, the narrator said that no laws of physics would be violated if the speed was different in each direction, but then he didn't go into any laws of physics. He just talked about measuring time passage between events.

In reality, a whole heck of a lot of laws of physics would be busted if the speed of light was not uniform in every direction.

So, it's kind of a cool video, but I didn't really get its point. We really do know the speed of light. It really has been measured, although you can't measure it exactly the same way you would measure things that go much slower than the speed of light. If that was their point, then fine. If, on the other hand, they were suggesting that there really is some unknown thing about light that we have never confirmed, but just assumed, it's wrong.
Overall the point was missed. You should take a look at his vids since you like science.
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