Post by: jeffreyH on 18/04/2021 13:11:01
Post by: Halc on 18/04/2021 13:21:04
Does that count?
There were clocks at both ends (the experiment was done shortly after the invention of a clock more accurate than a sundial), but the clocks were not 'in sync'.
Post by: Bored chemist on 18/04/2021 15:10:46
Well, maybe it can or not- I guess it depends on your definitions.
But there's a streetlight at the end of the road and it's not been replaced by LED yet, so it is a sodium lamp.
And I can put a sodium lamp in a car and drive towards the streetlight.
And, in principle, i can allow light from both curses to fall on a photodiode and I will get a voltage from that diode corresponding to the difference in frequencies - one of my local sodium lamp and the other of the doppler shifted streetlight.
Since I know my speed and the beat frequency and the wavelength of the light, I think that's enough to let me calculare teh speed of light.
Equivalently, I can use a radar "speed gun" and a vehicle with a known speed to measure the speed of light.
Does that count as "one way"?
Post by: alancalverd on 18/04/2021 22:54:54
Post by: CliffordK on 19/04/2021 06:36:11
Here's how I would do it.
SpeedOfLight.gif (9.32 kB . 669x311 - viewed 45038 times)Light (strong laser) passes through two shaft connected spinning discs, hits a cylindrical (conical) mirror, and is projected onto a wall to record. Mostly interested in the trailing edge of the light spot.
Light speed is: 299,792,458 m/s.
So, say the two discs are spaced 10 meters apart, then it will have traversed the gap in about 1/(29,979,245) s
Say the discs are 2 meters in diameter, and spinning at 60,000 RPM (1,000 RPS). With a circumference of πD, or 6.28 m.
So, your discs are spinning at 6,280 m/s.
Multiply the two, and one gets about 1/4774 m, or .0002094 m (2x10-4)
Multiply by 1000, and one is 0.2094 mm
That is well within the range one can discern.
The problem is the accuracy of the reading. If one uses UV light, one might be able to get down to 100nm accuracy, or about 1x10-7 m.
So that gives one about 3 digits of accuracy. One may be able to add a 4th digit, or even 5th digit by going with a faster shaft speed, longer shaft, larger discs, etc. Perhaps using X-Rays if they could be reflected on the cylindrical mirror (or mirror pair).
So, the question is would say 3 or 4 digits of accuracy matter?
Now, let's consider some kind of unknown aether or fabric of space(time).
What is the fastest object known to man? well, Earth is a good candidate.
The equator is rotating at about 460m/s. And, even doubling it for the difference of forward rotation vs reverse rotation with respect to the fabric of space during the 24 hour day, and it still isn't fast enough.
Earth's orbital velocity around the sun is about 29,780,000 m/s, or about 1/10,000 the speed of light. And, still not fast enough to pick up. Earth's orbital speed around the Milky Way is about 220,000 m/s, and getting close to 1/1000 the speed of light. And, the Milky Way is moving at about 600,000 m/s.
Now, if our aether or fabric of space is not distorted by gravity, electrical fields, matter, etc, then one can choose a place to orient one's device East/West with respect to the galactic rotation or motion, or North/South with respect to the motion. This should give comparative velocities, but one is just barely on the cusp of being able to pick it up.
(oops, I got a conversion factor to mm off... but it means it is easier to snag the first digit of the speed of light with the theoretical machine, but still a difficult task to get multiple digits of accuracy).
Ok, thinking about this more, there are issues with the leading edge of the light from the first slot illuminating the trailing edge from the second slot making timing difficult.
One would likely fix that by either adding an adjustible flat mirror to the inbound light, or slightly changing the direction of the source. Adjust to both maximize the intensity of the output beam as well as maximizing the beam width coming off of the cylindrical mirror.
A concave mirror rather than a convex mirror would also work, but would flip the image. Parabolic?
Post by: evan_au on 19/04/2021 23:13:25
Quote from: Halc
Roemer was the first to measure the speed of light, and he did it using a 1-way method.He used the fact that the Earth's orbit takes it backwards and forwards over (part of) the distance to Jupiter's moons.
Does that make it partially 2-way?
See: https://en.wikipedia.org/wiki/R%C3%B8mer%27s_determination_of_the_speed_of_light
Quote from: bored chemist
I can use a radar "speed gun" and a vehicle with a known speedRadar/laser speed guns use the signal reflected from a moving object, and compare it with the source. So it's 2-way.
- But the Doppler method with a Sodium streetlight could be done moving away from the streetlight, so that would qualify. (Even though measuring the beat frequency of non-coherent light sources at optical wavelengths is a real challenge!)
See: https://en.wikipedia.org/wiki/Radar_speed_gun
Quote from: alancalverd
Generate a radio signal at a convenient frequency and measure the wavelength at any point, by any means you wish (diffraction, quarter-wave dipole...- Diffraction is measuring the difference between light taking two different paths; not back to the source, but it is 2 different paths. Maybe 1.5 directions?
- Measuring the wavelength by transmission-line effects in a line or a diploe (or in a laser cavity) depends on reflection from the ends of the transmission line producing nodes, so it is a 2-way method. It also produces the speed of light in a transmission line, not the speed in free space, which is what I think the OP was seeking.
Quote from: CliffordK
SpeedOfLight.gifThe diagram shows light passing in both directions (but not reflected back to the source as in the Fizeau/Foucault experiment).
- But the description does not seem to make use of this two-way transmission...
See: https://en.wikipedia.org/wiki/Fizeau%E2%80%93Foucault_apparatus
My conclusion - measuring the speed of light using light and motion in one direction only is tricky.
Post by: CliffordK on 20/04/2021 00:08:57
Right, two independent light sources, and essentially two independent experiments as independent controls. One only needs one light source.Quote from: CliffordK(https://www.thenakedscientists.com/forum/index.php?action=dlattach;topic=82170.0;attach=31761;image)The diagram shows light passing in both directions (but not reflected back to the source as in the Fizeau/Foucault experiment).
If the slits are statically aligned, the lasers and mirrors for the reverse direction experiment would be independent, but the same slits would be used.
However, the reason to study the one-way speed of light is to prove or disprove that it is the same as the two way speed of light. Thus, the interesting thing would be if one found discrepancies between the right to left speed of light vs the left to right speed of light.
One would likely mount the system on some kind of a circular rail or turntable, probably also reversible motor/gearing. So, one could point it in different directions, and completely reverse it. So, if it was calibrated at East/West, then rotate it to West/East and see if it gives the same results. And compare to North/South or South/North.
And, of course, run the experiment at least once a month for a year to see if there is an annual effect.
The thing would have to be run at a pretty high vacuum both because the speed of light is impacted by the atmosphere, and rotation speeds would be mighty high. I was hoping the edge of the discs would get up to about mach 20 if not greater. Magnetic bearings would be nice, but most are active systems which may or may not be as useful at high speeds. One would likely have a mechanical gearbox, although a magnetic gearbox (or partly magnetic gearbox) might be possible.
The design is very similar to the single slitted wheel or mirror experiments, but has a mechanical connection between the two wheels rather than depending on a reflection back. Thus, the reflection experiments use a much simpler apparatus and can cover large distances, but only get a 2-way result.
Post by: Bored chemist on 20/04/2021 08:52:55
Radar/laser speed guns use the signal reflected from a moving object, and compare it with the source. So it's 2-way.OK, So, you point a radar gun at me and walk away.
I hook up a receiver to a frequency counter and observe the doppler shift. From that I can calculate your speed or, if I know your speed, I can calculate C.
But does that mean that the oscillators in the two instruments constitute "synchronised" clocks?
Post by: evan_au on 20/04/2021 10:43:25
Quote from: boredchemist
does that mean that the oscillators in the two instruments constitute "synchronised" clocks?I would thaht this assumes synchronised clocks.
- The frequency synthesiser has to be locked to the frequency when it is not moving, so it can measure the change in frequency when the source is moving.
- Einstein had some criteria that to truly synchronise two clocks, they needed to be colocated and at rest, relative to each other. As soon as you accelerate one, or put it at a different gravitational potential, they are no longer synchronised.
- We can relax some of those constraints if you don't want to synchronise the absolute time, but only the rate of the clocks.
- And you can "cheat" by using a clock like the yellow sodium vapour lamp wavelengths, where the synchronisation is done for you by the wavefunction of a sodium atom (provided they are at the same gravitational potential, if you want to be picky!).
Post by: wolfekeeper on 20/04/2021 16:52:16
Is there any method that you can think of that could achieve this? Have a stab at it.No. There isn't any way to do this. All methods involve something having to go in two directions, either before, during or after the experiment and so are inherently subject to a delay due to the speed of light in both directions. If you even measure a distance light has to go in both directions.
Post by: alancalverd on 20/04/2021 18:16:24
All methods involve something having to go in two directionsApart from reply #3, above.
Post by: CliffordK on 20/04/2021 20:00:17
Well, in #4, I show light going in both directions, but it is only being measured in one direction at a time. The reverse direction is part of an internal control, and allowing measuring and comparing two independent directions at a time.All methods involve something having to go in two directionsApart from reply #3, above.
Generate a radio signal at a convenient frequency and measure the wavelength at any point, by any means you wish (diffraction, quarter-wave dipole, whatever) . v = fλ by definition.Interesting concept. Of course that requires v, f, & λ to all be measured independently. Frequency does require some type of a clock, but not necessarily synchronized with the first clock.
Say one has a light bulb releasing light in all directions. Is it guaranteed that the frequency and wavelength will be constant in all directions? Relativity would seem to indicate that it is not constant. Of course, any relativity distortion of matter could also be problematic even with a physical attachment device.
Astronomy has already taught us a few things. Identical "Clocks" on other stars send us light at different wavelength/frequencies. I.E. red shift/blue shift.
I wonder if one could measure redshift/blueshift right here on Earth. So you have your oscillator creating a coherent light source projected against a fixed mirror, say a few miles away. If synchronized right, it should cancel it out perfectly along all locations along the path. I.E. near the mirror, as well as near the source.
Any discrepancy in frequency/wavelength would indicate Earth being red-shifted/blue-shifted in relation to aether/fabric of space.
Post by: Bored chemist on 20/04/2021 20:23:06
Astronomy has already taught us a few things. Identical "Clocks" on other stars send us light at different wavelength/frequencies. I.E. red shift/blue shift.Interesting point.
If you could measure the speed of those stars with a ruler and a stopwatch then you could use the blue or red shift to calculate the speed of light.
Ordinarily, we do it the other way round.
It's the same maths as my suggestion of looking at two sodium lamps.
Post by: alancalverd on 20/04/2021 23:12:39
On the one hand, who cares? The question was whether you could measure speed in one direction, to which the answer is obviously yes.
Say one has a light bulb releasing light in all directions. Is it guaranteed that the frequency and wavelength will be constant in all directions?
Using my method, you can measure speed in any direction because the dipole and frequency meter aren't associated with the source in any unique orientation. And has been pointed out, the earth is rotating and orbiting, so however you define direction, it is varying all the time. So the fact that you get the same answer twice is proof that speed is not direction-dependent.
Post by: wolfekeeper on 21/04/2021 02:03:04
Nope. There are no exceptions. How are you going to measure the distance? You can't. If you have a ruler, the molecular interactions along the ruler are affected by the speed of light in both directions; because they're electromagnetic. Hence the shape of the ruler is changed by any velocity the ruler has.All methods involve something having to go in two directionsApart from reply #3, above.
In fact because you can do a velocity boost in any direction, you can easily see that it doesn't matter if the speed of light is different in different directions; it can't affect the result.
You always measure the one-way velocity to be 'c', even if it isn't, because everything changes around it, in just the right way to make it 'c'.
And it's a good thing. If it wasn't like that, objects would probably fall apart if they started to move.
Post by: CliffordK on 21/04/2021 02:36:52
Nope. There are no exceptions. How are you going to measure the distance? You can't. If you have a ruler, the molecular interactions along the ruler are affected by the speed of light in both directions; because they're electromagnetic. Hence the shape of the ruler is changed by any velocity the ruler has.
On my apparatus above one measures the right/left and left/right speed of light simultaneously but independently on the same fixed apparatus. So anything affecting one would affect both.
If one twists it from East/West to North/South, or looks at diurnal drift, then you might be able to argue matter is expanding or contracting (not counting temperature which would need to be controlled, but a vacuum might aid with temperature control).
Post by: wolfekeeper on 21/04/2021 05:01:20
Post by: alancalverd on 21/04/2021 09:08:03
How are you going to measure the distance?You don't have to in #3. You can measure wavelength two ways - dispersion angle from a diffraction grating or peak amplitude of a dipole aerial - with the two instruments effectively at right angles, simultaneously.
Post by: evan_au on 21/04/2021 10:39:33
Quote from: alancalverd
dispersion angle from a diffraction gratingDiffraction gratings work by the fact that light takes many paths from the light source to the diffraction grating, and many paths from the diffraction grating to the screen/meter where the pattern is observed.
- Not exactly a 2-way measurement
- But not exactly 1-way, either!
You could do a similar thing with light echoes from a planetary nebula puffed off by a star which subsequently goes supernova: Observe the supernova via the direct light path, and then look for the delayed light echoes from the planetary nebula (which is not on the direct path).
- By looking at the delay between the direct path and the indirect path, you could calculate the speed of light
- But this is still using multiple paths for the light, and not just 1-way travel
- And this assumes that you know the straight-line distance to the star, which is hard to calculate by 1-way means (even parallax uses 2 light paths to determine a stellar distance)
Post by: Bored chemist on 21/04/2021 11:53:15
peak amplitude of a dipole aerialOnly works because you set up standing waves which require a reflection.
Post by: alancalverd on 21/04/2021 14:13:34
Post by: Bored chemist on 21/04/2021 14:55:37
No, a simple dipole aerial does not use standing waves.The signal strength is maximal when the dipole is a quarter wave long.Why?
Post by: alancalverd on 21/04/2021 17:37:57
Post by: Bored chemist on 21/04/2021 18:16:55
Because the potential difference between the poles is maximised.I didn't ask you to restate it, I asked you to explain it.
Post by: wolfekeeper on 21/04/2021 18:22:39
Uh huh. How you going to measure the pitch of the diffraction grating or the size of the aerial, using a one-way measurement?How are you going to measure the distance?You don't have to in #3. You can measure wavelength two ways - dispersion angle from a diffraction grating or peak amplitude of a dipole aerial - with the two instruments effectively at right angles, simultaneously.
There isn't actually any way to measure one-way speed of light. If you could do that, then the speed of light would not be 'c' and you'd be able to establish a universal rest frame. It's always 'c' in any measurement and you can't establish that.
Post by: Bored chemist on 21/04/2021 18:53:45
Uh huh. How you going to measure the pitch of the diffraction grating or the size of the aerial, using a one-way measurement?Hang on.
If you take that view then you can't measure the one way speed flight, but you also can't measure the one way speed of a Ford Fiesta, or anything else.
You can't even measure its length.
So "measuring the speed of..." or even "measuring..." becomes meaningless.
It turns out that you can't measure anything except the speed of light, and you don't need to do that because it's c.
Post by: wolfekeeper on 21/04/2021 20:05:18
Obviously that doesn't count for Ford Fiestas, because they go so much slower than the speed of light, although there is a fun puzzle which is somewhat related which goes:
"I drove a lap of a circuit in my Ford Fiesta at 60 mph, how fast do I have to go in the second lap to double my speed?"
Post by: Bored chemist on 21/04/2021 20:09:59
Obviously that doesn't count for Ford Fiestas, because they go so much slower than the speed of lightSo does Alan with his tape measure and dipole.
Post by: Bored chemist on 21/04/2021 20:12:11
"I drove a lap of a circuit in my Ford Fiesta at 60 mph, how fast do I have to go in the second lap to double my speed?"
If you can do it, you can do it by staying still.
Post by: evan_au on 21/04/2021 22:09:54
Quote from: alancalverd
a simple dipole aerial does not use standing waves.The signal strength is maximal when the dipole is a quarter wave long.The dipole radiated output is maximised when there is a resonance between the incoming frequency and the length of the dipole*
- At resonance (a standing wave effect), the voltage on the dipole is maximised, and the far-field (radiated) electromagnetic field is the strongest (for a given input voltage).
- At the end of the dipole conductor, there is an abrupt change in impedance, which reflects electrical energy back towards the feed point (and back down the feed wire to the transmitter)
- Amateur radio enthusiasts use a Standing Wave Ratio meter to tell when the impedances are best matched between the transmitter and the antenna, with minimum reflected power from the antenna.
See: https://en.wikipedia.org/wiki/SWR_meter
*In calculating the size required for the dipole elements, you don't use c=299,792,458 m/s, but you apply an "end effect" factor of around 96%, as electromagnetic signals travel slower in conductors.
See: https://www.electronics-notes.com/articles/antennas-propagation/dipole-antenna/length-calculations-equation-formula.php
- This article also has a nice graph of current and voltage in a dipole, which reveals a snapshot of the standing wave...
Post by: Bored chemist on 21/04/2021 22:24:15
Spoilsport, ;-)Quote from: alancalverda simple dipole aerial does not use standing waves.The signal strength is maximal when the dipole is a quarter wave long.The dipole radiated output is maximised when there is a resonance between the incoming frequency and the length of the dipole*
- At resonance (a standing wave effect), the voltage on the dipole is maximised, and the far-field (radiated) electromagnetic field is the strongest (for a given input voltage).
- At the end of the dipole conductor, there is an abrupt change in impedance, which reflects electrical energy back towards the feed point (and back down the feed wire to the transmitter)
- Amateur radio enthusiasts use a Standing Wave Ratio meter to tell when the impedances are best matched between the transmitter and the antenna, with minimum reflected power from the antenna.
See: https://en.wikipedia.org/wiki/SWR_meter
*In calculating the size required for the dipole elements, you don't use c=299,792,458 m/s, but you apply an "end effect" factor of around 96%, as electromagnetic signals travel slower in conductors.
See: https://www.electronics-notes.com/articles/antennas-propagation/dipole-antenna/length-calculations-equation-formula.php
- This article also has a nice graph of current and voltage in a dipole, which reveals a snapshot of the standing wave...
I was waiting for Alan to try to answer in a way that didn't use the word "resonance" (even though the page he cited mentions it a lot.).
It's pretty obvious that the only way the signal "knows" what the antenna impedance might be is that it goes to the end + bounces back.
Without that there's no way to build up the voltage to a maximum.
Post by: wolfekeeper on 25/04/2021 01:30:39
Post by: CliffordK on 25/04/2021 18:56:09
FWIW Veritasium has a video about this exact topic:Just because something hasn't been done doesn't mean it can't be done.
It's Impossible
When I was growing up there was a discussion about the limits of light microscopy, at around the wavelength of light (1/2?).
Today there are multiple methods that break that limit. Or, perhaps it is not as much breaking the limit, as finding ways around the limit.
Post by: wolfekeeper on 27/04/2021 05:04:07
You can't do it. In order to double your average speed, you'd have to go infinitely fast on the second lap."I drove a lap of a circuit in my Ford Fiesta at 60 mph, how fast do I have to go in the second lap to double my speed?"
If you can do it, you can do it by staying still.
Post by: Bored chemist on 27/04/2021 18:54:28
OK, so that's what the first clause of my answerYou can't do it. In order to double your average speed, you'd have to go infinitely fast on the second lap."I drove a lap of a circuit in my Ford Fiesta at 60 mph, how fast do I have to go in the second lap to double my speed?"
If you can do it, you can do it by staying still.
If you can do it, you can do it by staying still.
refers to.
But there's a cop-out.
What about if you can do it?
Is there a way it might not be a trick question requiring infinite speed?
And the answer is yes, sort of.
If the question was set by someone unsure of the difference between speed and velocity.
It's a lap of the track, so the net distance traveled is zero (you end up in the same place as the start).
So the average velocity of the car is zero. (Whatever the speed might be).
And you can double that by standing still.
So, if the person who asks can be talked into muddling velocity and speed, then you can do it.
BTW, did you really think I couldn't do basic arithmetic?
Post by: wolfekeeper on 27/04/2021 19:02:11
Post by: gem on 29/04/2021 00:41:21
Is there any method that you can think of that could achieve this? Have a stab at it.Similar to the sodium lamp, I believe it would be possible to derive the speed of light using the red/blue shift due to interaction of light with a gravitational field, for example
https://en.wikipedia.org/wiki/Pound%E2%80%93Rebka_experimenthttp://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/gratim.html
Post by: Bored chemist on 29/04/2021 10:07:33
Hi allIs there any method that you can think of that could achieve this? Have a stab at it.Similar to the sodium lamp, I believe it would be possible to derive the speed of light using the red/blue shift due to interaction of light with a gravitational field, for example
https://en.wikipedia.org/wiki/Pound%E2%80%93Rebka_experiment
http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/gratim.html
Post by: gem on 29/04/2021 19:35:25
Thank you BC
Post by: jeffreyH on 16/05/2021 22:47:25
Post by: alancalverd on 16/05/2021 23:28:42
"I drove a lap of a circuit in my Ford Fiesta at 60 mph, how fast do I have to go in the second lap to double my speed?"
Second lap speed = x.
Average speed = (60 + x)/2 = 120
x = 180. So I wouldn't use a Fiesta, but no problem with a F1 car or a small plane.
I suspect you have not formulated the question quite as you intended.
Post by: Halc on 17/05/2021 01:30:53
The Fiesta then completes the first lap in time t and the second lap in t/3 for a total of 4/3t for 2 laps, or 2/3 t average per lap, when you'd need 1/2 t average to have the speed double."I drove a lap of a circuit in my Ford Fiesta at 60 mph, how fast do I have to go in the second lap to double my speed?"
Second lap speed = x.
Average speed = (60 + x)/2 = 120
x = 180.
You are one of many who don't know how to compute average speed. Average speed is total distance/total time.
You are spending only a fourth of your time going the fast speed, and yet you are averaging it equally with the time spent going 60, a classic mistake.
Post by: Bored chemist on 17/05/2021 08:58:14
"I drove a lap of a circuit in my Ford Fiesta at 60 mph, how fast do I have to go in the second lap to double my speed?"
I did something.
How fast do I have to do it to double my speed?
Well, obviously, twice as fast. That's what doubling your speed means.
The "puzzle" doesn't say anything about averages, does it?
You are one of many who don't know how to compute average speed.Nobody was asked to.
So Alan's comment, and yours don't make sense.
I think this
I suspect you have not formulated the question quite as you intended.may be the salient point.
Post by: Bored chemist on 17/05/2021 09:04:10
Construct a device in the shape of an equilateral triangle. Place two lasers at corner A and targets at corners B and C. Have a second laser at corner B and a clock at corner C. Fire the two lasers at corner A simultaneously. One at corner B and the other at corner C. When the light is detected at corner C start the clock. When the light is detected at corner B fire the laser at corner B towards corner C. When the light from corner B is detected at corner C stop the clock. This device will work in any orientation to measure any discrepancy in the expected value for the speed of light.You might want to draw a diagram.
It won't stop you being wrong, but it might help us explain why you are.
Post by: alancalverd on 17/05/2021 10:34:10
You are one of many who don't know how to compute average speed. Average speed is total distance/total time.No, that's speed averaged over a fixed distance. Average speed is the average of all speeds.
Post by: Eternal Student on 17/05/2021 15:23:06
Construct a device in the shape of an equilateral triangle......I loved that as an idea and it seemed for a while that it could even work. Well done jeffreyH.
This seems to be the diagram as requested by Bored_Chemist:
A - - - - - - B
\ /
\ /
\ /
C
But equilateral and done with a graphics package that I can't be bothered with. Twin lasers at A and clock and C.
The problem seems to involve firing the twin lasers from A. You can't assume that light has reached all the way to B just because it has reached C and caused the clock to start. It may be that the light hasn't reached B yet (if light travels slower in the AB direction) or alternatively that B has already fired its laser and light is half-way up the line BC before the clock starts (if light travelled faster along the AB direction).
So it seems that what you're measuring with the time interval on the clock at C isn't how long it takes light to travel along BC but instead how long it takes light to travel an unknown distance and along what could be two different directions.
You'd have to write out the maths and tell us more about exactly what you were hoping to measure, JeffreyH, before I can be certain what you had hoped to do with that apparatus.
Post by: jeffreyH on 17/05/2021 19:40:33
Post by: jeffreyH on 17/05/2021 19:43:07
Post by: Bored chemist on 17/05/2021 21:12:15
we know the speed of light.No we don't.
Post by: jeffreyH on 18/05/2021 08:18:06
we know the speed of light.No we don't.
OK but now you are being pedantic. We know what the speed of light in a vacuum should be.
Post by: David Cooper on 22/05/2021 06:23:28
It should be fairly easy to calculate the one-way speed of light. The problem is doing so with any reasonable amount of accuracy.
Here's how I would do it.
Light (strong laser) passes through two shaft connected spinning discs, hits a cylindrical (conical) mirror, and is projected onto a wall to record. Mostly interested in the trailing edge of the light spot.
The shaft will twist if it's aligned with its direction of travel, so the slits won't both be at the top or bottom at the same time as each other. If you imagine two clocks at either end of the shaft with their dials aligned with the discs and with a nanosecond hand going round, the alignment of the apparatus and its speed of travel will affect the synchronisation of the two clocks, so the hands, just like the slits in the discs, will not always both be at the top or bottom at the same time, even if they are when the apparatus is at rest. Move it to the right and the clock (and disc) to the right will lag in its timing compared to the clock (and disc) to the left. This, in combination with length contraction, will always completely mask the differences you're trying to measure.
Post by: yor_on on 09/06/2021 18:00:44
And then you have that possibility in where it all becomes a sham. No 'propagation' at all, just a ideal expression, to us defined as a 'speed' inside our four dimensional SpaceTime.
spelling
=
Thinking of it, you might even be able to join those two into one. As that 'quantum dot' representing a ideal local 'tick' or 'clock' should be equal to all other, locally defined, 'ticks' or clocks. Assuming it's scalable into a macroscopic universe. you would then have a 'absolute time' scaling down, and a 'relative time' scaling up. Crazy, isn't it :)
Post by: Halc on 10/06/2021 11:31:10
Excellent analysis of the rotating cylinder thingy. Yes, per RoS, a rigid rotating cylinder will be twisted relative to a frame in which it has linear motion along its axis of rotation, which is not immediately intuitive.
Meanwhile, the line of clocks to measure expansion thing contradicts established science and has been split off here:
https://www.thenakedscientists.com/forum/index.php?topic=82441.0
Post by: David Cooper on 11/06/2021 00:30:53
Construct a device in the shape of an equilateral triangle. Place two lasers at corner A and targets at corners B and C. Have a second laser at corner B and a clock at corner C. Fire the two lasers at corner A simultaneously. One at corner B and the other at corner C. When the light is detected at corner C start the clock. When the light is detected at corner B fire the laser at corner B towards corner C. When the light from corner B is detected at corner C stop the clock. This device will work in any orientation to measure any discrepancy in the expected value for the speed of light.
Let me add a point D half way along the line BC. I'm doing this so that I can describe the direction AD. If the apparatus is stationary or moving in either direction along the line AD, the light from A will reach C to B simultaneously. If they both send a pulse at each other, they will meet at D while passing each other and reach their target corner simultaneously too.
What happens though if the apparatus is moving in the direction BC instead? Well, the light from A will reach C before it reaches B, so C will start its clock before B sends out its signal and, when you combine this with the length contraction acting on the equilateral triangle (which is now contracted in the BC direction), the timing difference that you're trying to detect will be completely masked.
All experiments of this kind are rendered useless by the masking that is bound up in the phenomenon of relativity, apart from the type that's been described at the link in reply #52 where established science conflicts with itself.
Post by: Just thinking on 18/06/2021 00:00:39
one way speed of light ..PNG (34.18 kB . 896x849 - viewed 3901 times)Yes by using the earth and the moon to view a distant moving object. If we were to place a telescope with a camera on the moon with a transmitting device that can detect and tracked Jupiter and register the very moment that one of the moons of Jupiter has just alined its edge with the edge of Jupiter sending a registration tone back to earth at that very moment we would no the one way speed of light. How, well here on earth using simple mathematics we would no the very moment that this alignment would take place on the moon without being there. So we could say the alignment is taking place now and see if the message from the transmitter arrives at the expected time. The time would be expected to be according to the distance of our moon from the earth at that moment in time. The experiment could be carried out by a maned or unmanned mission.
Post by: Just thinking on 06/07/2021 06:26:08
No we don't.Can I challenge you Bored chemist to see if you are able to pick apart my method of measuring the one way speed of light? Good luck.
Post by: Kris Kuitkowski on 06/07/2021 07:32:24
we need to redefine simultaneity. My proposition is as follows:
if a rigid body AB of length l perpendicular to X axis is moving without any acceleration parallel to X axis and at time t0 its point A is at location (x,0) then simultaneously its point B is at location (x,x+l)
Let's now design the experiment to synchronize distant clocks and measure one way speed of light:
Imagine four spaceships flying as perfect square EFGH towards (or away from) not moving (at least relative to each other) points ABCD, where AD is parallel to EF and distance EF equals AD. Points EG should be collinear with points AB and points FH collinear with CD. Making sure that ABCD (and EFGH) is a square is relatively easy, since 2-way speed of light is constant:
we can measure (and correct, if necessary) distances BD and CA by sending light signals from B to D (and from C to A) and back
Now at certain time (clocks at A and D can be pre-synchronized using Einstein convention, but it is not absolutely necessary) we can measure distance from A to G (L) and from D to H (L’) using light (laser) signal send from A to G (and reflected back to A) as well as distance from D to H. If the distance AG (L) equals DH (L’) signals from A and D had been sent simultaneously; if not, it would be easy to adjust the clocks so they are synchronized.
Please let me know if I made any wrong assumption
Of course, theoretically it would be sufficient to have only the lines AD parallel to GH, but practically it could be difficult to make sure they are parallel to each other
Post by: Bored chemist on 06/07/2021 10:14:03
Can I challenge you Bored chemist to see if you are able to pick apart my method of measuring the one way speed of light?Are you sure you want to?
Post by: Eternal Student on 06/07/2021 10:44:11
we need to redefine simultaneity. My proposition is as follows:
if a rigid body AB of length l
I'll re-read your article later when I have more time. Straight off the bat my first concern is that you are using Rigid Bodies in the context of Special Relativity. They just don't behave (or exist) in the way you may have hoped.
See, for example: https://einstein.stanford.edu/content/relativity/q2018.html for a short explanation of the problem.
Or the Wikipedia entry about "Born Rigidity", although this is a bit more involved or complicated.
None the less, you've got some good ideas and thank you for spending some time here. It doesn't seem as if you are asking the rigid bodies to accelerate so you may not run into too many problems, I'll have to re-read what you've written later.
Best wishes to you.
LATE UPDATE: I've had a bit more time to read and look at the diagram. The distance L' does not seem to be the distance DH as you have written but instead it is the distance DH' . I can't follow the diagram, sorry.
Post by: Just thinking on 06/07/2021 13:23:33
Quote from: Just thinking on Today at 15:26:08Yes please it would be all my pleasure.
Can I challenge you Bored chemist to see if you are able to pick apart my method of measuring the one way speed of light?
Are you sure you want to?
Post by: Just thinking on 06/07/2021 14:06:41
Yes please it would be all my pleasure.I forgot to mention it is just up a little at reply # 54.
Post by: Bored chemist on 06/07/2021 16:49:33
Is there anything special about "the very moment that one of the moons of Jupiter has just alined its edge with the edge of Jupiter", or are you just using it as an event which we can see from Earth or the Moon?
Would it make any difference if we replaced it by a bright flash on the surface of Jupiter?
Post by: Just thinking on 06/07/2021 17:16:11
Is there anything special about "the very moment that one of the moons of Jupiter has just alined its edge with the edge of Jupiter", or are you just using it as an event which we can see from Earth or the Moon?The alinement is very important as seen from our moon as it will act as a timed moment that we on earth can use to coincide with the time delay eg. the moon telescope sees this event and sends to earth a registration of the event as it takes place we will see if the message arrives back on earth about 1-second later as this is the distance of our moon 1 second from the earth if the signal arrived let's say in 0.5 seconds that would mean that light would take 1.5 seconds to reach the moon from earth.
Post by: Just thinking on 06/07/2021 17:20:24
Would it make any difference if we replaced it by a bright flash on the surface of Jupiter?Yes, that would not work as it would require a double journey and that would defeat the purpose of the experiment. One way speed of light.
Post by: Bored chemist on 06/07/2021 17:24:01
it would require a double journeyWhy?
We could just send a big firecracker to Jupiter .
It would flash and the light would come to us (and the moon) there's no two way journey made by the light, is there?
Post by: Just thinking on 06/07/2021 17:39:44
Quote from: Just thinking on Today at 02:20:24No that still won't work as the firecracker on Jupiter would be delivered by a rocket that has a so-called synchronised time that would be relied on to detonate the flash and that time synchronised system is the very thing that we are trying to avoid as it can not be relied on due to the time dilation and distance in space.
it would require a double journey
Why?
We could just sens a big firecracker to Jupiter .
It would flash and the light would come to us (and the moon) there's no two way journey made by the light, is there?
Post by: Bored chemist on 06/07/2021 17:48:12
We don't know when and where it happens without bouncing light off Jupiter.
But say we just use the sort of fuse they have on fireworks; you know that it will fire about 15 seconds after you light the fuse.
Isn't that good enough?
As long as we keep a watch for it for a while after we send the signal to light the fuse we will see the flash here, and the camera etc on the moon will see the flash there.
We can still time the interval between when the signals get to us.
Post by: Bored chemist on 06/07/2021 17:49:29
is that it depends where you are, so it isn't a good thing to choose as a timing point.
Post by: Just thinking on 06/07/2021 18:14:51
The trouble with "the very moment that one of the moons of Jupiter has just alined its edge with the edge of Jupiter"Earth and our moon see Jupiter at the same moment in time as long as Jupiter and our moon are at a 90-degree position as seen from earth and we hear on earth can no what the moon can see at any given time by simple mathematical equations when the moon of Jupiter comes in perfect alignment as seen from our moon at that same very moment we would see the moon of Jupiter in a slightly different position but we still would no when it has reached alignment seen from our moon. When our moon sees that alignment and we would know that moment without the use of light or a synchronised time pice the telescope and system on the moon can send that moment back to us and we can determine the delay of that signal from our moon.
is that it depends where you are, so it isn't a good thing to choose as a timing point.
Post by: Just thinking on 06/07/2021 18:22:29
There is the same problem with "the very moment that one of the moons of Jupiter has just alined its edge with the edge of Jupiter"We don't need to bounce light off Jupiter the reflected sunlight is coming from Jupiter and arriving on earth and our moon at the same time provided that Jupiter and our moon are at 90 degrees as seen from earth.
We don't know when and where it happens without bouncing light off Jupiter.
Post by: Just thinking on 06/07/2021 18:32:53
But say we just use the sort of fuse they have on fireworks; you know that it will fire about 15 seconds after you light the fuse.I think I see what you saying and that is a very good way to go about it. That is if you are suggesting that the telescope on our moon sends the mesage at the very moment of the flash yes we could time that.
Isn't that good enough?
As long as we keep a watch for it for a while after we send the signal to light the fuse we will see the flash here, and the camera etc on the moon will see the flash there.
We can still time the interval between when the signals get to us.
Post by: Bored chemist on 06/07/2021 18:34:13
Earth and our moon see Jupiter at the same moment in timeNo, they don't.
Here's a picture.
As they are lined up, the camera on the moon can't see the moon of Jupiter, but the observer on Earth can see it.
That's why it's a good idea to have a time signal like a flash.
Also, the distance from (Jupiter's moon moon or Jupiter) to either the Earth or the Moon is different.
So your method doesn't even make sense,
https://en.wikipedia.org/wiki/Not_even_wrong
Post by: Bored chemist on 06/07/2021 18:36:41
OK, better late than never.But say we just use the sort of fuse they have on fireworks; you know that it will fire about 15 seconds after you light the fuse.I think I see what you saying and that is a very good way to go about it. That is if you are suggesting that the telescope on our moon sends the mesage at the very moment of the flash yes we could time that.
Isn't that good enough?
As long as we keep a watch for it for a while after we send the signal to light the fuse we will see the flash here, and the camera etc on the moon will see the flash there.
We can still time the interval between when the signals get to us.
Now, there's another clever trick to simplify things.
Rather than a camera and a signal sent to earth, why not just use a big mirror on the Moon?
If we set it up so that you can see the reflection of Jupiter (using another telescope on Earth) then we don't need to worry about how long the image processing takes.
Post by: Just thinking on 06/07/2021 18:48:14
* Moony.png (5.13 kB . 615x345 - viewed 2 times)Jupiter is over 2000 seconds away our moon is only 1 second away and that 1 second can be accounted for or if our moon and Jupiter is at 90 degrees seen from earth it can be cancelled out of the equation. And there are times when the earths moon is in a position that can see jupiter from the same angle.
Quote from: Just thinking on Today at 03:14:51
Earth and our moon see Jupiter at the same moment in time
No, they don't.
Here's a picture.
As they are lined up, the camera on the moon can't see the moon of Jupiter, but the observer on Earth can see it.
That's why it's a good idea to have a time signal like a flash.
Also, the distance from (Jupiter's moon moon or Jupiter) to either the Earth or the Moon is different.
So your method doesn't even make sense,
Post by: Bored chemist on 06/07/2021 19:01:28
The moon, the Earth and Jupitar are all moving, and two of them are rather awkward to get to.
This is the 21st century. It's easy to get a clock that will measure time intervals to better than a picosecond. That's time for light to travel about a third of a millimetre.
So, we can set up a "scale model" of your system.
In the lab we have a detector and a mirror a foot apart and (we have a really big lab) 2000 feet away we have a flash light
Post by: Just thinking on 06/07/2021 19:03:17
OK, better late than never.Well, the image processing time would be known and can be accounted for the amount of time would be very little as an 8-inch telescope will see the image and the camera will handle that light in a fraction of a second. The mirror idea is rather fanciful for a number of reasons such as it would have to be very large as the telescopes on earth or even the Hubble telescope can only see structures on the moon that are of a size far beyond many 10's of meters and that is with very pore clarity.
Now, there's another clever trick to simplify things.
Rather than a camera and a signal sent to earth, why not just use a big mirror on the Moon?
If we set it up so that you can see the reflection of Jupiter (using another telescope on Earth) then we don't need to worry about how long the image processing takes.
Post by: Bored chemist on 06/07/2021 19:05:41
So the detector will give two signals separated in time by some interval corresponding to how long it takes light to travel from the mirror to the detector (compared to taking the direct path).
And with modern electronics we can measure that accurately.
Post by: Bored chemist on 06/07/2021 19:06:24
The nice thing about a thought experiment is the budget is infinite.OK, better late than never.Well, the image processing time would be known and can be accounted for the amount of time would be very little as an 8-inch telescope will see the image and the camera will handle that light in a fraction of a second. The mirror idea is rather fanciful for a number of reasons such as it would have to be very large as the telescopes on earth or even the Hubble telescope can only see structures on the moon that are of a size far beyond many 10's of meters and that is with very pore clarity.
Now, there's another clever trick to simplify things.
Rather than a camera and a signal sent to earth, why not just use a big mirror on the Moon?
If we set it up so that you can see the reflection of Jupiter (using another telescope on Earth) then we don't need to worry about how long the image processing takes.
Post by: Just thinking on 06/07/2021 19:18:39
* Moony2.png (9.41 kB . 837x583 - viewed 6 times)i have another suggestion to make everything easier.This would seem to be a miniature version of my suggestion but in fact it is not the same concept as the smaller version is still reliant on a beam of light and it is the same beam of light that is reflected of the mirror this is one way light travel but we don't know the true time that it left its source. It still is reliant on synchronisation and that is the problem with this type of test.
The moon, the Earth and Jupitar are all moving, and two of them are rather awkward to get to.
This is the 21st century. It's easy to get a clock that will measure time intervals to better than a picosecond. That's time for light to travel about a third of a millimetre.
So, we can set up a "scale model" of your system.
In the lab we have a detector and a mirror a foot apart and (we have a really big lab) 2000 feet away we have a flash light
Post by: Just thinking on 06/07/2021 19:26:45
The nice thing about a thought experiment is the budget is infinite.That is very true I do believe that the mirror on the moon would work if the mirror and the telescope were large but it would be a lot of bad luck if that mirror was to break. Might leave that experiment to china.
Post by: Bored chemist on 06/07/2021 19:32:17
Because the distance from the flash to the mirror is exactly the same as the distance to the detector, the light reaches the detector and the mirror simultaneously.* Moony2.png (9.41 kB . 837x583 - viewed 6 times)i have another suggestion to make everything easier.This would seem to be a miniature version of my suggestion but in fact it is not the same concept as the smaller version is still reliant on a beam of light and it is the same beam of light that is reflected of the mirror this is one way light travel but we don't know the true time that it left its source. It still is reliant on synchronisation and that is the problem with this type of test.
The moon, the Earth and Jupitar are all moving, and two of them are rather awkward to get to.
This is the 21st century. It's easy to get a clock that will measure time intervals to better than a picosecond. That's time for light to travel about a third of a millimetre.
So, we can set up a "scale model" of your system.
In the lab we have a detector and a mirror a foot apart and (we have a really big lab) 2000 feet away we have a flash light
(I used a 2000 foot string to measure the distances when I set up the experiment)
Post by: Just thinking on 06/07/2021 19:42:25
Because the distance from the flash to the mirror is exactly the same as the distance to the detector, the light reaches the detector and the mirror simultaneously.Yes, now I see we just see the time difference from the mirror to the detector. That is the one-way speed of light mirror to the detector. Ok, I can see that so why do the scientists and professors question this method as it does seem to be the same consept that I have put forward only on a very larg scale.
(I used a 2000 foot string to measure the distances when I set up the experiment)
Post by: Bored chemist on 06/07/2021 19:44:35
Post by: Just thinking on 06/07/2021 20:19:51
OK, now watch the video; at least, watch the bit from about 4:15 to 4:45.I watched the full video it is very interesting and it is the age old argument referring to the two way speed of light. But the method that you used and the method that I suggest is the one way speed of light. Your method is a beam of light travelling from only one direction arriving at the detector and the mirror at the same time in space with the added distance of the mirror to the detector I cant see the problem with that. The only thing you need to do is now the added time from the mirror to the detector.
Post by: Bored chemist on 06/07/2021 20:42:48
Now imagine you are "God" sitting behind the detector, and you watch the flash of light.
You see some light come straight towards you and hit the detector.
And you see some light coming not quite straight towards you, it goes a bit off to the right, and it hits the mirror, and then it travels back to the left and hits the detector.
That's the bit where it's a 2 way experiment,.
If the L-R speed isn't the same as the R-L speed then you can't be sure (even though I measured the distances with a bit of string, that the light reaches the mirror at exactly the same time as it reaches the detector.
It may have got there a little early, or a little late.
So you don't actually know how long it too to cover the extra foot.
Essentially, because the light goes to the right and then to the left, it's not a one-way speed.
Can I challenge you Bored chemist to see if you are able to pick apart my method of measuring the one way speed of light? Good luck.I don't need luck; I have science.
Post by: Just thinking on 06/07/2021 20:43:42
Because the distance from the flash to the mirror is exactly the same as the distance to the detector, the light reaches the detector and the mirror simultaneously.You only need one timer for your experiment the timer registers the first strike of light and the second strike of light and the second strike of light will take the time of light to travel the distance of one foot. It is that time delay that is the one way speed of light. Ore am I missing something.
(I used a 2000 foot string to measure the distances when I set up the experiment)
Post by: Bored chemist on 06/07/2021 20:50:48
Ore am I missing something.You missed the entire point.
But yes, the timer starts counting when the first flash reaches the detector (directly) and stops when the second flash hits it (having bounced off the mirror en route).
The point is that the light goes off to one side, and then comes back.
So it's not a "one way" measurement.
Post by: Just thinking on 06/07/2021 21:01:51
OK the point he makes is that it impossible to tell if light travels right to left at the same speed that it travels left to right.Ok so there even fussy if the original light source travels a small amount out of alignment then what if your experiment was shifted from north to north west a 45 degree shift then would that hot yield different results if there was a change in light speed if light travels at different speeds in different directions a rotating light experiment of your type should reveal that.
Now imagine you are "God" sitting behind the detector, and you watch the flash of light.
You see some light come straight towards you and hit the detector.
And you see some light coming not quite straight towards you, it goes a bit off to the right, and it hits the mirror, and then it travels back to the left and hits the detector.
That's the bit where it's a 2 way experiment,.
If the L-R speed isn't the same as the R-L speed then you can't be sure (even though I measured the distances with a bit of string, that the light reaches the mirror at exactly the same time as it reaches the detector.
It may have got there a little early, or a little late.
So you don't actually know how long it too to cover the extra foot.
Essentially, because the light goes to the right and then to the left, it's not a one-way speed.
Post by: Just thinking on 06/07/2021 21:04:38
So it's not a "one way" measurement.That is true but it is not in opposite directions only a slite angle.
Post by: Bored chemist on 06/07/2021 21:34:01
Left is the opposite of right.So it's not a "one way" measurement.That is true but it is not in opposite directions only a slite angle.
It goes one way, then it goes the other.
So it is not a one-way measurement.
Post by: Just thinking on 06/07/2021 21:53:29
Left is the opposite of right.Why should your experiment fail if you change the angular position of the mirror and you find that the light reaches the detector at the expected time then how is it possible for light to be travelling at different speeds in different directions changes of angle and direction couldn't always cancel out to the same result? I think my plane is in the bin if you have debunked your own testing and slite angles matter what hope is there for finding the answer as it is I don't personly believe that light travels at different speeds in different directions anyway but it would be nice to be able to test it.
It goes one way, then it goes the other.
So it is not a one-way measurement.
Post by: Bored chemist on 06/07/2021 22:26:37
it would be nice to be able to test it.You can't.
At best you can show that a round trip along two lines gives a consistent speed.
Post by: Just thinking on 06/07/2021 23:15:16
You can't.I do believe that if the light speed is measured in Compleat opposite directions that the result will be the same even if the speed is faster one way than the other as one will cancel out the other. But on an angle a change in speed direction should be revealed as the balance of cancellation will be uneven. So my thought is that if light speed always balances out in opposite directions and it is of different speeds then an angle of attack should reveal this as it is no longer in opposite directions. This is why I feel the speed is the same in all directions otherwise the angle approach would have revealed the difference. Anyway, at the end of the day, we still get the same results all of the time. Thanks for your time Bored chemist going over this I will look at this from a different perspective now and see if I can come up with something else That's not a catch 22.
At best you can show that a round trip along two lines gives a consistent speed.
Post by: Just thinking on 06/07/2021 23:58:19
light speed circle.PNG (23.33 kB . 915x835 - viewed 2037 times)You can't.I just added this diagram of my light circle all speeds balance out in opposite directions to give 6 but out of alignment we get varying answers this is why I thought your experiment would work I think the reason for this is that the real circle has the number 3 in all directions.
At best you can show that a round trip along two lines gives a consistent speed.