Half a croissant, on a plate, with a sign in front of it saying '50c'
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Audio or digital relative time simulation

 Show how time is slower for someone riding away from you at the speed of sound
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Or simulate that with a digital radio delay.

Option 1. Audio time travel.

An audio device beeps every second. The beep is a note starting with Middle C and going up each time by one note. There's a powerful flashing light sending a flash every second through a cycle of White Red Green and Blue.

At time 0, when the device is close up we hear the first beep with the C note immediately, and see together with it the first flash of white light.

Time 0s summary:
Distance: 0.
Flash #0 White.
Beep #0 C.
See: Flash #0 Red.
Hear: 1st heard beep: Beep #0. C

Time 1s: Traveling away from us at the speed of sound, after one second it is about 343 meters away. We see the second flash in red, but it will take the sound 1 whole second to get to us, so we will hear the B note only after 2 seconds from when the vehicle left us.

Time 1s summary:
Distance: 1x343 meters.
Flash #1 Red.
Beep #1 D.
See: Flash #1 Red.
Hear: Nothing. (as expected)

Time 2s: Another second passes, we are now at time 2s. We see the third (green) flash, but hear the second D note. We know that the device is now beeping. It previously beeped at time 0s with note C, then at time 1s with note D, and now, at time 2s it is beeping for a third time with the note E. It will take this third beep two full seconds to reach us. So we will hear it only at time 4s.

Time 2s summary:
Distance: 2x343 meters.
Flash #2 Green.
Beep #2 E. Will be heard in 2 seconds at time 4s.
See: Flash #2 Green.
Hear: 2nd heard beep: Beep #1. D (We already heard beep #0 C)

Time 3s: The device has been travelling for 3 seconds now away from us at an approximately constant speed of 343 meters per second so it should be approximately 343x2 meters away from us.

Beep #3 (we started with beep #0) with note F is sent out along with a fourth flash, in Blue. We see this flash which in our minds is "almost immediately" but do not hear any beep at this moment, and don't expect to either. The F note beep that we sent is expected to reach us in another 3 seconds at time 6s.

Time 3s summary:
Distance: 3x343 meters.
Flash #3 Blue
Beep #3 F. Expected at time 6s.
See: Flash #3 Blue.
Hear: Nothing (as expected. Till now we heard C and D)

The device's black box has been recording all along the device's own beeps, timing them with it's own independent clock, according to which at device time d0s it emitted the C note, at device time d1s it emitted the D, at d2s the E, and at d3s the F.

Reversal: The vehicle now stops and immediately begins coming back towards us at the speed of sound. (No worries, there it is on a magnetic rail which is not in our direct path, and all safety precausions have been taken by an expert team. so what could go wrong?

Reversal summary: At time of reversal we are at time 3s.
Which we have just summarized.

Time 4s: Our distance has now decreased by 1 second of travel from 3s (3x343 meters) down to 2s (2x343 meters).

The device beeps a G note which is the 5th beep and flashes white (again), the 5th flash and first of the new four color cycle (starting with 0). This white flash is seen immediately, but the note G sound will take 2 seconds to reach us, expected at time 6s (along with the former F note emitted just 1 sec ago from a distance of 3 seconds away). But at this time we DO hear the beep from 2s with the E note. (So by now we have heard C, D and now E)

Time 4s summary:
Distance: 2x343 meters.
Flash #4 White (again).
Beep #4 G. Expected at time 6s (together with F.
See: Flash #4 White.
Hear: #2 E (after hearing C,D before)

Time 5s: We are now 1s away. The emitted sound (#5 beep, tone High A) will reach us within 1s at time 6s. The flash #5 is Red, seen immediately.

Time 5s summary:
Distance: 1x343 meters.
Flash #5 Red
Beep #5 High A. Expected at time 6s (together with former F.
See: Flash #5 Red.
Hear: Nothing. (Till now we have heard C,D and E)

Time 6s - We are back home. The device flashes Green, and beeps #6 tone High B.

We hear the sound from time 3s: #3 F.
We hear the sound from time 4s (emitted two seconds ago) #4 G.
We hear the sound from time 5s (emitted one second ago) #5 High A
We now hear the final beep, emitted just now, beep #6 High B.

All four come in together. If we would be traveling with only the audio records of time, a millisecond before the signals came in, we may think that the device has not aged and is still waiting to reach its 3rd second although we are already in the 6th.

This proves that time was slower for the audio time-counting device.

Option 2. Digital radio delay time travel simulation:

Same thing but this time its a computer animation creating a radio time delay, with music played in a zoom session, slowing down as we get further away and speeding back up all of a sudden at the last second we get back.

Option 3. Stupid reporter nodding head time travel simulation.

The reporter tells us the time every second and waits to hear us confirm before continuing, stupidly nodding until she or he hears us.

—pashute, Aug 29 2021

Artificial Doppler effect Could be used to generate the beep [pocmloc, Aug 29 2021]

[link]






       Beep would be doppler shifted unless you used conveyor-belt-mounted speakers. Because you and device are both immersed in air which is the carrying medium for the sound.
—pocmloc, Aug 29 2021
   

       I was actually hoping someone would explain why this isn't so with light, and how Einstein took the light experiment (or thought experiment?) to show that time in fact ran slower for the traveler.   

       I don't get it. In any case time "catches up with me" when I finally make it back. When I'm 1 sec away whatever signal it is will catch up in the next sec. When I was 2 seconds away it will get there in 2 seconds. So when I travel back, the stationary guy always perceives all the signals coming in at the same final moment! But we know that's just the signal reaching us now, and when the man was "looking at time locally" it was at the "first person"'s pace.
—pashute, Aug 30 2021
   

       I suppose the explanation is is something like, light travels at the speed of light, and if you travel away from me through spacetime at a speed a and emit light, then the light leaves you at the speed of light c and travels through spacetime at speed c and hits me at speed c.   

       Sound doesn't work like that - if you travel away from me through the air at speed a and emit sound, then the sound leaves you at speed L-a and travels through the air at speed L and hits me at speed L   

       So in summary time is slower for you if you travel away from me at a significant fraction of the speed of light, because time has to adjust to make the speed of light a constant c no matter how fast you are going. But there is no such constraint on the speed of sound, it is fixed relative to the medium and can change relative to the emitter or receiver through simple arithmetic (speed of sound in air plus speed of emitter or receiver through air).   

       This is not a very good or probably even a very correct explanation, but I;'m spinning it off the tp of my head. You'd be better off finding someone who knows what they are talking about rather than asking whack-heads on a stupid ideas website
—pocmloc, Aug 30 2021
   

       You could also look at info on aeroplanes flying faster than the speed of sound. The sonic boom is a feature of the speed of sound being relative to the medium (air) and not relative to the moving aeroplane. Light does not behave like this, there is no medium and it is constant relative to the source and to the observer and to everyone and everything else inbetween.
—pocmloc, Aug 30 2021
   

       //Light does not behave like this, there is no medium and it is constant relative to the source and to the observer and to everyone and everything else inbetween//   

       Light changes in frequency by the time difference for two entities moving together or apart. Same as sound does. It's when you bring in a third observer that my brain breaks.
—Voice, Aug 31 2021
   

       [pashute] - in your example, you have the pitch changing with the time/distance travelled. In fact the pitch would be proportional to the velocity, so if this remains constant, the pitch of sound heard by the stationary observer would remain constant. Pitch-shifting in sound, like time-dilation, is proportional to acceleration, not speed. As for time dilation, this is real, and doesn't "catch up" when you get back, as confirmed by synchronising very accurate clocks, putting one in an aeroplane and flying around with it for a bit, and then comparing the two clocks.
—hippo, Aug 31 2021
   

       Are we getting confused between speed of propogation, and frequency? I know I am!
—pocmloc, Aug 31 2021
   

       Light is quantum message object. Seeing something is different to the actual experience. The observer sees the message, the rocketeer experiences time like treacle because of acceleration causing a compressed/bunched up block of spacetime. Well that's how I imagine the situation.
—wjt, Sep 04 2021
   

       I have experienced some treacle that was quite time-like, in the sense that there was never as much of it as I wanted.
—pertinax, Sep 05 2021
   

       OK my pitch example was not a good one. I should have said there's a short bell ringing several times according to the point it reached. At the first initial second it sounds off one ring, after one second it rings off two rings, and after two seconds it sounds off three rings etc.   

       I'm talking at a constant speed of sound rate in a consistent and constant temperature and pressure of air.   

       And I'm waiting to hear the experts. I know two of them passed away, and I miss them very much, but there are still others here who could explain. Light travels at a constant speed which means it reaches a certain distance at a certain time. So there should be no reason why coming back at the speed of light the sound should not reach me at the designated times I have spoken about.   

       Better yet: Let's have a stationary transmitter at each point. It emits the signal and compares the local clock with that of the clock on the ship. At point 3s the ship's clock is at 3. It will take 3 seconds for the signal to reach us. It took the ship 3 seconds to reach it, so the time on the ship's watch is 3. So we will hear the 3s signal after 6 seconds. On the way back at point 2s it took 4 seconds to reach it. 3 seconds to reach point 3s, and another 1 second to reach back to 2s. The ship's time is 4. We will receive the 2s station's signal in 2 seconds, which by us will be time 6s. So when it gets back to us the audio clock did not change its time. In what way is this different from light?
—pashute, Sep 10 2021
   

       OK my pitch example was not a good one. I should have said there's a short bell ringing several times according to the point it reached. At the first initial second it sounds off one ring, after one second it rings off two rings, and after two seconds it sounds off three rings etc.   

       I'm talking at a constant speed of sound rate in a consistent and constant temperature and pressure of air.   

       And I'm waiting to hear the experts. I know two of them passed away, and I miss them very much, but there are still others here who could explain. Light travels at a constant speed which means it reaches a certain distance at a certain time. So there should be no reason why coming back at the speed of light the sound should not reach me at the designated times I have spoken about.   

       Better yet: Let's have a stationary transmitter at each point. It emits the signal and compares the local clock with that of the clock on the ship. At point 3s the ship's clock is at 3. It will take 3 seconds for the signal to reach us. It took the ship 3 seconds to reach it, so the time on the ship's watch is 3. So we will hear the 3s signal after 6 seconds. On the way back at point 2s it took 4 seconds to reach it. 3 seconds to reach point 3s, and another 1 second to reach back to 2s. The ship's time is 4. We will receive the 2s station's signal in 2 seconds, which by us will be time 6s. So when it gets back to us the audio clock did not change its time. In what way is this different from light?
—pashute, Sep 10 2021
   
      
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