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Take three light valves. They need to be very fast. Put them in a stack. Sequence them so that they open and close
one after each other, timed such that each one opens and closes a certain amount of time after the previous one,
where that amount of time is the time it takes light to travel from one
valve to the next.
This is analogous to the three-solenoid peristaltic pump for fluids described in [1], except that it doesn't pump the
light along—it just allows it through in one direction but not the other, by timing the valves to match the
propagation of the light. It does, however, result in a reduction in effective brightness of the light it allows through
in that direction, by only allowing 1/3 of it through, and produces a very fast (invisible to humans) flickering.
49/343 [2018-05-17]
[1] Three-solenoid peristaltic pump [PDF]
https://abcm.org.br...ORS/SSM4_VII_07.pdf
[notexactly, May 19 2018]
One-way Glass
The idea that inspired this one. [notexactly, May 19 2018]
scissors that are not faster than light
http://math.ucr.edu...ty/SR/scissors.html
[beanangel, May 19 2018]
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How fast? How close together? |
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One light-nanosecond is about one foot. A rapatronic
camera's shutter can open for as short a time as 10 ns
according to Wikipedia. I don't know at the moment how the
three valves' timings will affect the math, but this gives an
order-of-magnitude estimate of ten or twenty feet. Of
course, faster light valves might have been developed since
then. |
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This is quite a cool idea, at least as a thought experiment. |
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Well... that's conceivably nuts. |
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I'ma posit that given perfect reflectors, light will still make its way out (though even then you'd be talking a 20ft input path and (at least) a 40 ft exit path which is still really weird) |
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A Kerr cell shutter can open and close in nanoseconds, and has the
secondary benefit of involving interesting chemicals with "nitro" in their
names. |
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One issue is that the timings will be different for off-axis light. If the timings are too tight, you would only be able to see a single spot of light through the window. |
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// One issue is that the timings will be different for off-axis
light. // |
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That's why I didn't put it in home:window:privacy like the
inspiring idea. I thought this would be more useful in
scientific and engineering applications, where you can
guarantee on-axis light. |
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How is this different (in its effects) from a single light valve that's
open one third of the time? |
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How do you synchronise their opening and shutting? Seeing as how there will be a time lag from the open and shut signal travelling down the wire? Do you need each one connected to its own atomic clock? Or can you offset the synchronisation signal to accomodate the predicted time delay? Or could the pulse of light itself be used to synchronise in one direction? |
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It's not beyond the wit of man to model the delay of pulses
propagating down transmission lines. |
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So, you basically just cut a few bits of coax to the correct lengths, and
connect them all to the same pulse generator. |
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Obviously, the coax length needs to be a bit longer than the speed-of-
light distance from the pulse generator to the shutters! |
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I am reminded of the faster than light big scissors, the tips of which travel faster than light [link] Just make one, or three, of these and see what it does. Oh, oops, the scissors thing has been refuted... |
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There is another scheme that might be called marquee lights... |
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It's not the tips that travel faster than light (if they
approached the speed of light, they'd become infinitely
massive, and you couldn't move them). It's the contact point
between the blades that travels faster than light. And the
contact point can indeed travel at any speed, including faster
than light. |
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Interesting idea. There are a few simple refinements
that might push this towards practical usefulness. |
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First, you don't need 3 shutters, just 2, and you can make
it work with a theoretical best case attenuation of only
50%. |
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Assuming a perfect 10ns shutter open time, have shutter
1 and shutter 2 separated by 5 light nanoseconds. open
shutter 1 from time 0 to time 10ns. Open shutter 2 open
from time 5ns to time 15ns. Repeat the cycle every 20ns.
Light passing through shutter 1 from 0 - 10ns, will arrive
during the shutter 2 open time of 5 - 15ns. Light passing
through shutter 2 at 5ns to 15ns will arrive at shutter 1
when it is closed between 10ns and 20ns. |
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Another optimization is to put a material with high
refractive index between the shutters. This would have
two benefits. First, the light will travel slower, requiring
less distance. Second, the refraction would somewhat
straighten off-axis light. Using polycarbonate with a
refractive index of 1.6, slows light down to 188,000 km/s,
reducing the 5 light ns distance from 1.5m to 0.94m.
Depending on your budget, you might try a more exotic
materiel with an even higher index. |
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If 1 meter is still too thick, you can't find any better
shutters, and you're willing to have more attenuation, you
can play with the shutter timing to make it work. For
example, say we can have only 2 light ns between the
shutters. In that case, if shutter 1 is open between 0 and
10ns, and shutter 2 is open from 8ns to 18ns (still
repeating every 20ns), light will get through for 4 ns
every 20ns, so there will be 80% attenuation. |
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Off axis light isn't too big of an issue. Let's say we want
to deal with light at up to a 45 degree angle not using a
refractive material. at a 45 degree angle, it will take
7.07ns instead of 5ns to go between shutters. In order to
prevent light going backwards we'd need to increase the
time when both shutters are closed by 2.07ns (from 20ns
to 22.07ns). This will of course slightly increase the
attenuation of light passing in the desired direction. For
the first timing example 10/22.07 = 45% of on axis light
will be transmitted. Off axis light at a 45 degree angle
will have (10-2.07)/22.07 = 36% transmitted. |
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Hmm, split zer old photon, send one bit down the old
Peristaltic one-way light valve and see what happens. |
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//scissors that are not faster than light |
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Well if they were, we wouldn't be able to see 'em. Tieing
bits of string on them would aid retention. |
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Are there relativistic issues to do with synchronising time to this accurately in different places? |
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Thank you, [scad mientist], for doing a bunch of math in support of
the idea. I didn't feel up for doing it. Also, I had thought of the two-
shutter version, but I didn't feel like doing even the mental simulation
to decide whether it was viable, and I forgot to include any mention of
it in the idea. (I'm just glad I remembered as much as I did; I forgot
most of the points I wanted to include right before I typed it up, and
had to struggle to remember them.) So thanks for bringing that back
up and showing its viability. I think all of that qualifies you to be a co-
inventor on the patent (lol). |
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// Are there relativistic issues to do with synchronising time to this
accurately in different places? // |
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No. Well, you might have to consider relativity in designing the
system, but it would not be a fundamental obstacle to the possibility
of doing so. |
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Could you do this with a simple mechanical device? |
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Imagine a thick disc of opaque, light-absorbing material,
fixed on an axle. Now drill holes through the disc. The
holes are angled, relative to the direction of rotation. Now
we shine light at just one part of the disc (say, a sector
from "2 o'clock" to "4 o'clock"). |
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If the disc is stationary, and light hits the disc face-on, no
light will pass through because it will hit the (angled) walls
of the holes. However, if the disc is spinning at the right
speed, light *will* pass through the holes in one direction,
because the angled hole will be constantly moving into
alignment with the photon as it passes through. But light
should not pass in the other direction, because the angled
hole will be moving out of alignment. |
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The only problem will be that the disc has to be very thick,
or it has to spin very very fast, or has to have very narrow
holes (probably limited by the wavelength of light,
otherwise diffraction and stuff will kick in). |
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That's analogous to how the speed of light was measured by
a few historical scientists, so I expect it'd work. |
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//Imagine a thick disc of opaque, light-absorbing
material, fixed on an axle. Now drill holes through the
disc.// |
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I immediately thought of the dual discs in a spinning disc
confocal microscope, or rather the two-way path through
the lower Nipkow disc. I remember a conversation with a
chap from Zeiss who said they had to take into account
the delay in the emission light relative to the excitation.
Pretty snazzy at the ~10-20 cm light path distances they
deal with. However, I expect MOST of that delay is the
kinetics of fluorescence emission lifetime I expect. We
have lasers that will happily control light pulses down to
femtoseconds, dividing by 10^-15 gives satisfying power
numbers. |
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//MOST of that delay is the kinetics of fluorescence emission
lifetime I expect. // Fluorescence lifetimes are typically oto
a nanosecond, which is one light-foot. So that's significant
but not huge compared to the light path. |
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