Why Flat Earth Laser Tests are Misleading

[Mick West]

Source: https://www.youtube.com/watch?v=ookTfBP5sUU


When you shine a laser beam across the surface of a lake, it is very prone to refraction, but often this is ignored, and the result is declared a victory. Laser tests are a very poor choice of a test of curvature, when much clearer (and easier) tests are available, such as looking at large objects (like mountains) over water.

In the video above, I describe the problem, and answer this question:

With a resounding "YES, OF COURSE". It's actually really common for conditions to exist where a low-level laser is visible to a low-level camera many miles away. In fact, we are generally seeing this type of curvature most of the time during the day when the ocean is cooler than the air. We just don't really notice the very thin strip of compression near the horizon. The laser makes it stand out.

 

[Mick West]

In the video I mention a test at Brighton where conditions exist for downwards refraction. Here's the test:


Source: https://www.youtube.com/watch?v=mKrZnKu9ID4


Showing this temperature gradient:
View attachment 36691

that's at 1.5°C thermal inversion over 2m, you can get the lasers visible with 0.2°C
https://www.metabunk.org/refraction/?~(p~'Brighton*20to*20Worthing*20Pier)_
View attachment 36692

 

[Bryan Olson]

Great, but I do not see how a constant angle of beam divergence helps get over the curve. With one milliradian divergence, if only the bottom of the beam reaches the camera, we could just aim the laser half a milliradian lower and the middle of the beam would then reach the camera.
Would more divergence help get over the curve? A light bulb has the full 2 pi radians, but I don't think it's any more visible given the same positions.
Refraction is certainly a factor, and perhaps could increase the angle of beam divergence with distance, or even the diffraction effect from being partly blocked by water could, but I don't think the constant angle helps.

 

[Mick West]

Great, but I do not see how a constant angle of beam divergence helps get over the curve.

The main contribution it has to the results being misleading is that it extends the beam downward. So if they have a beam that is parallel to the ground, there's always going to be a light path that goes directly to just skimming the horizon, the region of greatest refraction. The yellow line in the video

This misleads because they think the center beam should not be visible because not only is the laser hidden by the hidden value, the center of the beam is the "drop" above the surface - which is even more.

The Brighton test folk say:

Since their laser is at 1.5 m and "level", they (seemingly) are not considering the air below 0.5m. However, the beam WILL spread down to that region, and their temperature reading show a quite significant temperature gradient, with the air above the water 0.5°C cooler than the air at 1.0m.

Of course this effect is less if you have a less divergent beam. But the Brighton tests use a standard $15 green laser, like mine, which has a 1.0 mrad divergence.

Having LESS divergence will not make it impossible to see the laser, it just makes it more dependant on the angle.

For example, here I've reduced the divergence to 0.05 mrad. The beam still diverges, but now I have to tilt it down from level by 0.026° to make it visible. Notice it's a lot brighter too, as it diverges less.

(I accidentally put the boat with the laser at 7 miles here, but still no problem seeing it)

 

[Bryan Olson]

Did the Brighton testers claim to precisely level the laser? I thought they were testing solely for visibility over the curve, and were free to play with the aim.

Having LESS divergence will not make it impossible to see the laser, it just makes it more dependant on the angle.​

O.K. From how the video named beam divergence along with refraction I had thought you were suggesting that divergence helps get around a curve as refraction does.

 

[Mick West]

Did the Brighton testers claim to precisely level the laser?

Not directly, but note they say: "between 0.5m and 1.5m there was no density gradient measurably", so they are not considering the air below 0.5m, which would indicate they don't think the beam goes into that air. They had the lasers and cameras at 1.0m.

 

[JohnP]

With reference to the second video:
Why should what happens in the troposphere have any effect on a horizontal laser beam (particularly in a Flat-Earth model)? Many of the sources (e.g. Wikipedia) that tell you about the temperature rising in the troposphere will also tell you what is happening to the density of the air. (Hint: it is the air density that is mostly reponsible for changes in refractive index.)

 

[Landru]

Hey Mr. West!

I've found two objections to your explanation.

mod Deirdre edit: first ex removed. unclear and impolite.

And secondly, it has been claimed that at night, the air is usually colder than the water which means that the laser should bend in an upward direction. Many flatearthers claim that there is no footage of laser beams bending downwards.

Cf.
Source: https://www.youtube.com/watch?v=VPlCnbOhBRg
time stamp: 10:28

I'm going to give you a chance to fix this. You state:

And secondly, it has been claimed that at night, the air is usually colder than the water which means that the laser should bend in an upward direction. Many flatearthers claim that there is no footage of laser beams bending downwards.

Do not paraphrase. Where is it claimed?

 

[Hepper]

I'm going to give you a chance to fix this. You state:

And secondly, it has been claimed that at night, the air is usually colder than the water which means that the laser should bend in an upward direction. Many flatearthers claim that there is no footage of laser beams bending downwards.

Do not paraphrase. Where is it claimed?

It is claimed at 10:28 in the second video that I posted. It states:

[...] the air above the sea will be warmed and be less dense than the air above it. So, under everyday "normal" conditions, in the evening and at night the air above the sea will be denser the higher up it is.

What we need in order for West's idea to work is the opposite: Dense air immediately above the body of water.

And at 6:44, the maker of the video states:

No luck finding pictures and videos of downward refraction on google and Youtube? That's odd!

Of course, this last sentence is sarcastic.

 

[Laser]

@Hepper - There are a couple problems with Dr.JohnD's claims about the air above the water. One is that, although it is true that all else being equal, colder air is denser, for air of increasing altitude above the water, all else is not equal. The altitude is increasing and therefore the pressure is dropping. The density decrease due to pressure drop usually dominates the density increase due to temperature drop. This is obvious when you consider the very low densities and very cold temperatures at very high altitudes, and how the warmer air at sea level is more dense. But that's probably not the main problem with Dr.JohnD's theory. He fails to establish that the water is actually warmer than the air over his entire laser or observation path. Indeed just the opposite. Mick West showed that some of Dr.JohnD's own videos showed height compression of the lower floors of the distant sky scrapers, betraying the downward bending of light. Dr.JohnD made a rebuttal video but failed to produce a valid refutation.

As for the lack of pictures of downward bending lasers, that is due in part to the many miles of distance needed to show noticeable laser bending, and the spreading out and dimming over long distance of even very well columnated lasers. Also, remember that not only will the laser be bent down, but the light scattered from the beam that allows you to see the beam, will also be bent down on its way to the eye/camera, and therefore the distant parts of the beam will appear higher than they really are, instead of you seeing the true shape of the beam curvature.

 

[Hepper]

@Hepper - There are a couple problems with Dr.JohnD's claims about the air above the water. One is that, although it is true that all else being equal, colder air is denser, for air of increasing altitude above the water, all else is not equal. The altitude is increasing and therefore the pressure is dropping. The density decrease due to pressure drop usually dominates the density increase due to temperature drop. This is obvious when you consider the very low densities and very cold temperatures at very high altitudes, and how the warmer air at sea level is more dense. But that's probably not the main problem with Dr.JohnD's theory. He fails to establish that the water is actually warmer than the air over his entire laser or observation path. Indeed just the opposite. Mick West showed that some of Dr.JohnD's own videos showed height compression of the lower floors of the distant sky scrapers, betraying the downward bending of light. Dr.JohnD made a rebuttal video but failed to produce a valid refutation.

As for the lack of pictures of downward bending lasers, that is due in part to the many miles of distance needed to show noticeable laser bending, and the spreading out and dimming over long distance of even very well columnated lasers. Also, remember that not only will the laser be bent down, but the light scattered from the beam that allows you to see the beam, will also be bent down on its way to the eye/camera, and therefore the distant parts of the beam will appear higher than they really are, instead of you seeing the true shape of the beam curvature.

Do you have a link to the corresponding videos? Another criticism that I think is worth mentioning is the brightness of the laser. It decreases over long distances. According to Mr West, what we see when we observe the green/blue flashes of light is actually the edge of the bottom radius of the laser beam, not the intense central axis. However, this portion of the laser should be barely visible due to the decrease in brightness (at least according to the critics). But most flat earthers clearly observe a very intense and bright flash of light as soon as they spot the laser.

moderator deirdre

mod edit: video example removed due to impolite thumbnail and it isn't a video example just a photo, which is here:

So how could this be? Is it because the diverging beam directly enters the eye of the observer?

 

[Mick West]

According to Mr West, what we see when we observe the green/blue flashes of light is actually the edge of the bottom radius of the laser beam, not the intense central axis.

That's not what I'm saying at all. The spread of the beam simply makes it a bit easier to aim. Any part of the beam can be visible based on what angle the laser is initially at.

 

[Hepper]

Thanks for the clarification. Something that I (and many flat earthers) still don't understand about refraction is the following: Why does refraction only affect distant objects? Why does the laser appear to be elevated (due to the change in the angle of the incoming laser beam) but not the bulge of water behind which the source of the laser is located?

 

[Mick West]

Why does refraction only affect distant objects?

The longer the distance, the more refraction. This is because the refraction is very gradual, caused by the slight vertical gradient in the air. This is very different from the sudden transition between air and water. So nearby objects are affected, just not enough to see. Kind of like how haze is in all the air, but nearby objects don't look hazy, because you are not looking through much air.

Why does the laser appear to be elevated (due to the change in the angle of the incoming laser beam) but not the bulge of water behind which the source of the laser is located?

Both are elevated. But since the laser is further away than the horizon, it is elevated more than the horizon.

 

[Hepper]

And I also don't fully understand how a vertical gradient can affect the path of the laser. This is much more easy to imagine when considering atmospheric refraction of sun light (which makes the sun itself appear elevated), because in this case, the light rays from the sun are moving through all the air layers of the atmosphere. But how is a horizontal laser beam affected by a vertical gradient?

 

[Mick West]

But how is a horizontal laser beam affected by a vertical gradient?

The horizontal beam is still made up of vertically oriented waves of light. The bottom of each wave is in denser air than the top (even over 1mm), so it travels slower, turning the direction of travel of the wave downwards.

 

[FatPhil]

The horizontal beam is still made up of vertically oriented waves of light. The bottom of each wave is in denser air than the top (even over 1mm), so it travels slower, turning the direction of travel of the wave downwards.

This is one of those cases where simplifications help make the effect make sense to those unfamiliar with the concept, but alas is more an "as if" than a "because". The "light travels slower in denser air" part is accurate, and fortunately that's all you need to explain refraction (as long as you accept Maxwell's equations). It's best to keep the "tops" and "bottoms" of the waves out of the explanation. As soon as you start introducing concepts such as polarisation, that explanation breaks down.

Dr. Don Lincoln at Fermilab did a couple of explanatory youtube videos that cover why bending of light happens at an air/glass interface, and the same principles apply to smoothly changing densities:
CUjt36SD3h8 Why does light slow down in water?
NLmpNM0sgYk Why does light bend when it enters glass?
(Yes, that is how I interface with youtube, with raw ids and youtube-dl, their website doesn't work in my browser at all nowadays.)