Photographing light

[jpm (Phil McCurdy)]

YEC proponents sometimes use the pretty fanciful argument that we cannot measure the speed of light, so it may spread instantaneously in one direction, making the measurement of time irrelevant to the distance of astronomical objects.

Here is a video and article that is very interesting in its own right, actually photographing light in transit. Incredible feat on its own, but since it is also an observation of light in transit, would it not also be a direct observation of the speed of light, making the aforementioned argument void?

YouTubers Filmed The Speed Of Light At 10 Trillion Frames Per Second

[paleomalacologist (David Campbell)]

If anyone is up on details of relativity, that would help. My physics gets through several years of grading calculus-based intro physics for work study, so I don’t know all the details…

My impression is that this technically doesn’t void the argument because this shows light going sideways relative to the camera and the YEC claim is that light traveling towards the observer is travelling instantaneously. Quibbles about vacuum may also be possible.

However, the fact that your GPS works does void the argument. Light can carry information. If light towards an observer is travelling at infinite speed, we should see things truly in real time. Rather than seeing the Big Bang, we ought to see the distant objects as they are now. We won’t be able to use GPS because the clock signals from all the satellites will show the same time no matter how far away they are from us if the anisotropy argument is correct.

[jammycakes (James McKay)]

@jpm

YEC proponents sometimes use the pretty fanciful argument that we cannot measure the speed of light, so it may spread instantaneously in one direction, making the measurement of time irrelevant to the distance of astronomical objects.

Ah yes, Jason Lisle’s Anisotropic Synchronisation Convention. The argument is that we can’t measure the one-way speed of light, so it could in theory be infinite heading towards us and c/2 heading away from us.

The ASC is technically correct. It’s basically choosing a different coordinate system, in which, say, you could have a clock at supernova SN1987A (168,000 light years away) set to February 23, 1987 on the day that the supernova exploded, so that when the signal reached us that would be the date that it read. However, if you bounced the signal back, it would still read February 23, 1987 while the clock at the supernova had moved on to read 333,987 AD in the meantime. However, if you used this alternative coordinate system (you could rewrite Maxwell’s Equations and possibly even e=mc^2 in this reference frame), you would end up with some insanely complicated maths. Which is why nobody in their right mind actually uses such a convention.

So where’s the falsehood then? The falsehood is not in the physics, but in identifying it as young earth creationism. It is nothing of the sort. It is day-age creationism pretending to be young earth creationism.

[rsewell (RON SEWELL)]

By Lisle’s ASC, the speed of light as a function of direction relative to the observer (θ) is given by cθ = c/(1-cos(θ)), where θ = 0 indicates the direction directly toward the observer. Although he does not state it, I presume he is taking some sort of limit for the denominator, so that he is not dividing by zero.

Under ASC, the one-way speed of light when directed toward observers on earth is axiomatically infinite, even though the round-trip speed of light remains 3 × 108 m/s. Thus, the light from stars that are created on the fourth day will reach the earth essentially instantaneously.

My understanding of Lisle is that while his focus is on Earth, every point in the entirety of the universe observes any given event as it happens, as per his equation. Two remotely situated observers immediately detect incoming light or gravitational waves from any position in deep space, irrespective of distance traversed.

Lisle’s following assertions seem consistent with conventional understanding:

1. It is not feasible to measure the one way speed of light.
2. All methods of synchronizing clocks, such as slow separation or sending of a signal, are equivalent.
3. Selection of a convention is a mapping function, and thus arbitrary.

Where Jason Lisle’s convention is distinct in its orientation to observers. As far as I can tell, usually discussion and experimentation around the isotropy of the speed of light concerns differences that may exist with respect to direction in a given frame. This is not Lisle’s interpretation. According to him, two gun slingers who face each other with dueling laser guns will have light propagating towards both targets at infinite speed, while that same light will be propagating away from the laser guns at half the round trip speed of light, so that there can be no defined speed of light that can be assigned to the space where those beams meet in the middle.

Gravitational waves are clearer in that they travel at the speed of light, but without concerns for line of sight or obstructions, the processes which produce them are short and sharp compared to those for light, and detection facilities must put effort into precise timekeeping in the course of their investigations.

Should gravitational wave events impinge on the earth from anywhere on a three dimensional axis, if those waves propagate at infinite speed, they will arrive instantaneously at each detector station. All observatory stations will timestamp any events with the same pattern irrespective of direction. It does not matter if the stations were synchronized under assumptions of ESC, ASC, or set using knock off watches from a street market. What matters for this point is not the accuracy of triangulation, just that the pattern of timestamps would be identical regardless of the direction of the source on the celestial dome. Therefore, under ASC, triangulation is impossible. Note that this same consideration does not apply if light is asymmetrical in a fixed direction. This is not an argument that two way speed of light must equal the one way, only that at a given time there must be directionality if timestamps are to be consistent with direction of propagation.

I am emphatically not objecting to the idea that the speed of light can be different by direction. Rather, it is to point out that Jason Lisle, in setting the speed of light to be in respect to the observer rather than a given frame, is positing that the speed of light is infinite from any direction, and therefore differential times of arrival cannot be used to determine direction. If a person looks up at a clear night sky, she will see constant light from stars from every bearing. According to Lisle’s convention, the light from all these stars has arrived instantaneously. Thus, the speed of light has nothing to do with direction in an inertial frame. Light travels at different speeds for two facing observers with dueling laser guns even if they are close together in the same inertial frame.

My questions for Lisle would be, one, if light is instantaneous to the observer from all directions, how could the time interval for timestamps vary by direction? Two, if the intervals for the timestamps are in fact identical regardless of direction, how would it be possible to triangulate the gravitational wave source? This is a work a day practical matter of real world operation for astronomers, not just some coordinate system convention. I would suggest that Lisle’s ASC predicts that triangulation is not possible, and the fact that triangulation has been done falsifies his observer centric version of light travel anisotropy.

I am no physicist. If I am just not getting it, I would be happy to have an explanation of how to triangulate using ASC assumptions, without recourse to conventional coordinates.

To sum

Gravitational waves are line of sight
Triangulation is time of flight
Therefore, Lisle is not right

[jpm (Phil McCurdy)]

Great explanation, but in the high speed observation made in the article referenced, they should be able to measure speed of light propagation semi-directly (through light produced as it passes a medium, which should not effect the speed of propagation) , so would that not be a measurement of the speed of light showing that

@rsewell

Lisle’s following assertions seem consistent with conventional understanding:

1. It is not feasible to measure the one way speed of light.

Is indeed false. And of course that he is wrong, something we can all agree on. Or am I seeing it wrong?

[rsewell (RON SEWELL)]

@jpm

so would that not be a measurement of the speed of light showing that

@rsewell

Lisle’s following assertions seem consistent with conventional understanding:

1. It is not feasible to measure the one way speed of light.

Is indeed false.

I’m convinced by simplicity alone that the speed of light is isotropic, but that is not empirical proof of course.

The immediate reply one could expect from Lisle is that the experimental results are as predicted by his convention, given that the direction of travel is perpendicular to the observation.

This apparatus displays the propagation of the scattering of light from a pulse, and is essentially a light echo. This is interesting, because light echos from cosmic events have been observed in space. The objection has been raised against Lisle that a mirror more that three thousand light years distant in space would not reflect an image back to Earth, because by his equation the light from earth would still be en route. Of course, such a test is not feasible, but light echos amount to the same thing and may be a realistic test of Lisle’s model.

[St.Roymond]

@jpm

Here is a video and article that is very interesting in its own right, actually photographing light in transit. Incredible feat on its own, but since it is also an observation of light in transit, would it not also be a direct observation of the speed of light, making the aforementioned argument void?

Wow, and wow.

I expected to see a smooth motion, but the light seemed to flow unevenly. Anyone have a clue what’s happening there?

Anyway . . . Dr. Jason Lisle just got sunk. I can’t find that they’ve calculated a speed of light using this awesome toy, but that’s not necessary to debunk Lisle; it demonstrates that the speed of light is finite. Though I suppose to really slam him they should do the filming with a variety of orientations of the camera – including vertically so Lisle can’t claim they haven’t actually tested his notions.

@jammycakes

it could in theory be infinite heading towards us and c/2 heading away from us.

Except the question then is “away from whom?”

[St.Roymond]

@rsewell

According to him, two gun slingers who face each other with dueling laser guns will have light propagating towards both targets at infinite speed, while that same light will be propagating away from the laser guns at half the round trip speed of light, so that there can be no defined speed of light

But isn’t that a contradiction? It has the photons going two different speeds at the same time.

[rsewell (RON SEWELL)]

@St.Roymond

But isn’t that a contradiction? It has the photons going two different speeds at the same time.

It does seem absurd to me. By ASC, where the dueling laser pulses meet in the middle, there is a definite point in space time where each observer’s coordinate system intersect, but there is no speed of light defined generally or by direction. And as radiation and information is reaching to and from everywhere in the universe, by Lisle every point in the cosmos gets its own special snowflake coordinate origin in splendid isolation.

[jammycakes (James McKay)]

@St.Roymond

Anyway . . . Dr. Jason Lisle just got sunk. I can’t find that they’ve calculated a speed of light using this awesome toy, but that’s not necessary to debunk Lisle; it demonstrates that the speed of light is finite.

So I’ve been looking into this a bit more and reading up about it. Here are a few resources of note. First, this Veritasium video explains the problem: you can’t measure the one-way speed of light because you need two synchronised clocks to do so, and you can’t synchronise your clocks without first knowing the speed of light in that direction. Catch 22.

Why No One Has Measured The Speed Of Light

Interestingly, he actually addresses this particular example: the researchers aren’t just measuring light travelling through the bottle; they’re measuring light travelling through the bottle and then from the bottle to the camera. Consequently, it doesn’t measure the one-way speed of light after all, but only a round trip as before.

This is a problem that physicists have been trying to work round for more than a century without success. He cites two papers. Greaves et al (2009) thought they had found a way round it, but Finkelstein (2009) authored a rebuttal shortly afterwards pointing out that their measurement had been a round trip after all.

Could you get round it by taking cosmological observations – for example, distant galaxies and the cosmic microwave background? One would have thought so, but Lewis and Barnes (2020) did the calculations and found that the different relativistic effects would cancel each other out even in this case as well. This news article on phys.org provides a simple explanation why.

In other words, it turns out that the Anisotropic Synchrony Convention is mathematically legitimate. It may sound bizarre, counterintuitive and even outright ridiculous, but it’s not something that we can falsify through measurement – or at least, not using any measurement technique that we know of.

So where does this leave Jason Lisle?

First of all, the ASC is simply a different frame of reference. The RationalWiki article about it makes an important point that what Lisle is doing is similar to using a reference frame in which the Earth stands still and the whole universe rotates around it. Such a reference frame isn’t much use for examining the properties of the universe as a whole (not least because it would have distant galaxies moving at a rate of 90 billion light years a day) but it does have some use in explaining where “fictitious forces” such as centrifugal force and the Coriolis force (the force that makes your bath water empty clockwise) come from. However, unlike a rotating frame of reference, I’ve no idea what practical use the ASC would serve in Real Life.

Secondly and most importantly however, as I’ve already pointed out, the ASC is not a young earth model but a day-age model. It still recognises that there is a frame of reference in which the Earth is 4.5 billion years old and the universe is 13.8 billion years old after all—and moreover, that frame of reference is much more intuitive, much simpler mathematically, and much more in line with Occam’s Razor. In that respect, it’s simply a more complex variety of the rather hand-waving argument that cites time dilation as a way of getting six 24 hour days out of billions of years.

[Mervin_Bitikofer]

@rsewell

The immediate reply one could expect from Lisle is that the experimental results are as predicted by his convention, given that the direction of travel is perpendicular to the observation.

So … what if they had turned the bottle so that it was angled mostly toward the camera (but still with a slight perpendicular component so that there would still be motion visible?) If the larger component of the vector motion was toward the viewing aperture, would that address this problem? Or what would that have revealed?

[St.Roymond]

@rsewell

By ASC, where the dueling laser pulses meet in the middle, there is a definite point in space time where each observer’s coordinate system intersect

I’m not getting the “in the middle” part. The two observers’ ‘coordinate systems’ intersect at every point along the way because at every point according to one observer a given photon is moving at infinite speed whereas to the other it is moving at c/2.

[St.Roymond]

@jammycakes

Coriolis force (the force that makes your bath water empty clockwise

Nope. Unless your bathtub water is perfectly still when the plug is removed, the net angular momentum of the water in the vicinity of the drain is greater than Coriolis force and thus determines the direction of the swirl – and if you pull the plug upwards through the water, that motion itself is sufficient to impart angular momentum. Additionally, any deviation in the drain opening from perfectly smooth and level will provide a force sufficient to override Coriolis. For that matter, whether or not there is hair in the drain (if you have a hair screen) imparts a greater force than Coriolis!
In my tub, the direction of spin will switch depending on which way I pull the plug, i.e. to the left or to the right because the pull actually rotates the plug.

Experiments have determined that in a perfectly round tub with a perfectly centered drain that is filled and the water allowed to sit most of a day so it will become still, the Coriolis effect only becomes observable after ten or fifteen minutes. Disturb the water though, for example by dropping a brick in, and the direction of drain swirl becomes unpredictable. Generally, the Coriolis effect in a bathtub-sized container is something like 10^{-4} smaller than other ordinary forces in play.

A rule of thumb is that if a body of fluid in motion isn’t visible from space, it isn’t big enough for Coriolis effects to dominate.

Besides which, bathtubs at the equator also end up with a vortex as the water drains!

[St.Roymond]

@jammycakes

Interestingly, he actually addresses this particular example: the researchers aren’t just measuring light travelling through the bottle; they’re measuring light travelling through the bottle and then from the bottle to the camera. Consequently, it doesn’t measure the one-way speed of light after all, but only a round trip as before

[Note that the image of light traveling through the bottle starts around 8:50. For the same in the OP video it starts about 4:32.]

But it isn’t a round trip: photons come out of the laser moving perpendicular to the camera, then some scatter and thus make their way to the camera, so the path is roughly a right angle – there is no return trip to make a round trip of it. For there to be a return trip the light would have to be coming from the camera.

I’ve been trying but I can’t figure out how there’s a round trip involved.

[jammycakes (James McKay)]

@St.Roymond

Nope. Unless your bathtub water is perfectly still when the plug is removed, the net angular momentum of the water in the vicinity of the drain is greater than Coriolis force and thus determines the direction of the swirl – and if you pull the plug upwards through the water, that motion itself is sufficient to impart angular momentum.

Thanks for the telling off. I should have known I’d get a pedantic response if I got sloppy like that on a forum frequented by scientists.

Let’s substitute hurricanes for bathtubs. Counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere.

@St.Roymond

But it isn’t a round trip: photons come out of the laser moving perpendicular to the camera, then some scatter and thus make their way to the camera, so the path is roughly a right angle – there is no return trip to make a round trip of it. For there to be a return trip the light would have to be coming from the camera.

You’d need to synchronise the clocks between the laser and the camera, so there is that to it as well.

For the difference between different points, note that the path is only roughly at a right angle. I’m presuming that the situation here is similar to what he talks about when he addresses the possibility of moving the clocks apart slowly – differences in the angle may be small but would cancel out the other relativistic effects, especially if you’re working with c_\theta = \frac c { 1 - \cos \theta } as @rsewell mentioned. I suppose one would need to do the maths to confirm that that’s the case.

[rsewell (RON SEWELL)]

@St.Roymond

For there to be a return trip the light would have to be coming from the camera.

I as well thought the Veritasium video blew past that. The laser has to be coordinated with the camera to fire, but other than that there is no measurement involved just to generate the pulse. There is one clock at the camera, which registers a tick when the laser pulse scatters upon entry, and another tick when pulse exits. That would be the measurement. Of course, there is undetermined one way travel to the camera, but the time there should be very similar for the entry and exit and so should cancel out. You cannot measure the one way speed of light if separated clocks or a round trip are involved, but I need someone to lay out what the gotcha ( there always seems to be one ) is here.

@jammycakes

For the difference between different points, note that the path is only roughly at a right angle.

Even if the apparatus is angled, the detected light is always direct, otherwise it would miss and not observed at all. With a finite speed of light, the travel time from scatter to detect would vary with the trigonometric distance involved, but with infinite speed it would make no difference. By Lisle’s equation, all observed light arrives instantaneously from where it was last emitted or reflected or refracted or scattered or whatever.

[St.Roymond]

@rsewell

By Lisle’s equation, all observed light arrives instantaneously from where it was last emitted or reflected or refracted or scattered or whatever.

Yes – so even if the light reaching the camera traveled instantaneously, the light traveling through the bottle is still doing so at a measurable speed.

[jammycakes (James McKay)]

@rsewell

I as well thought the Veritasium video blew past that … I need someone to lay out what the gotcha ( there always seems to be one ) is here.

You’re right there, he does hand-wave it a bit. It would be good if he cited a source for this particular case, and that’s really what this thread is all about after all. Another case I’ve wondered about is multiple images of the same supernova appearing at different times in distant galaxies due to gravitational lensing.

Would be good for someone like @pevaquark to weigh in on this one here.

[paleomalacologist (David Campbell)]

From what I know of Lisle’s claims, he is indeed saying that the light is coming at infinite speed towards observer A and at c/2 away from light-generator B at the same time. This avoids being disproved by the failure to find a difference in the speed of light for round trips in various directions (Michelson–Morley, etc.). But if Lisle’s model were correct, if you and I have atomic clocks one light-second apart, you can beam me a live stream of your clock and I can set my clock to match it, because light comes at infinite speed towards me. I beam a live stream of my clock back to you. It should match the time on your clock because it is travelling at infinite speed towards you. But the reality is that you see a time that is two seconds behind your clock. GPS uses this principle, which is why I am confident about how the experiment turns out.

Now, this experiment does not prove that the speed of light is isotropic; it could travel faster one way and slower the other and still average out to a 2 second difference. But Lisle’s claim that the light goes faster for both observers runs into problems with this experiment. As jammycakes already pointed out, Lisle’s model also does not actually help much with promoting a young earth.

[rsewell (RON SEWELL)]

@jammycakes

Another case I’ve wondered about is multiple images of the same supernova appearing at different times in distant galaxies due to gravitational lensing

Lisle explains this as light propagating off axis, and therefore not at infinite speed, but that highlights a shortcoming of his theory, that to my knowledge he has not formulated a general version, and it may not be possible in agreement with observation.

We say gravity bends light in the same way we say the sun sets - it is phenomenological language. Light always travels in a straight line along the geodesic of space. Light isn’t bent, space time is curved. As far as I know, Lisle has not addressed in what way his formula fits into the real universe which has mass and energy, and therefore curvature.