Timeline for In the twin paradox does the returning twin also come back permanently length contracted flatter than the twin on Earth?
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23 events
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| Mar 5, 2021 at 18:35 | comment | added | ralfcis | What about using two metronomes with two very long periods of swing. If time really does slow for the travelling twin, wouldn't the two metronomes be out of phase when they re-unite after a round trip? | |
| Feb 28, 2020 at 3:41 | comment | added | ralfcis | I assume you don't tutor. So I'll have to figure out how to make it work here. | |
| Feb 28, 2020 at 3:30 | comment | added | ralfcis | Dale, years ago I was permanently banned from there on my 1st question when I was even more ignorant. In order to avoid the personal theory stank, I'd have to know the correct answers before I asked the questions. I don't even have the terminology so I wouldn't last long. When my ban lifts here in 5 months, I will be re-banned in short order because no one wants to look at my math which shouldn't be looked upon as a personal theory because it's just math. | |
| Feb 28, 2020 at 3:20 | comment | added | Dale | @ralfcis yes, I am also quite active at physicsforums.com (actually more there than here). You will have to be careful there, we are fairly helpful for people trying to learn relatively but not tolerant of personal theories at all (explicitly against the rules). A lot of your posts feel like personal theories, so you would need to watch that carefully. | |
| Feb 28, 2020 at 2:57 | comment | added | ralfcis | @Dale I've re-read your answer and have realised you're the man. You understand my questions (it takes me longer to understand your answers). Since the PSX is not a discussion forum and since I'm silenced here, I'm wondering if you're on another forum where I can access your immense knowledge and open minded understanding. | |
| Oct 10, 2019 at 19:30 | comment | added | Dale | Yes, that is correct. The clock maintains a historical record, and so does an odometer (a difference, once accumulated, will never go away). A metronome does not have a record and neither does a ruler. | |
| Oct 10, 2019 at 18:10 | comment | added | ralfcis | Someone on another forum explained to me what you're saying. When a frame jump occurs, time and space effects are no longer reciprocal. Only one participant ages less but the space imbalance is in the distance travelled, not in a permanent flattening of the returning ship. Hence if your odometer could be made, it would record the ship has travelled a contracted distance. | |
| Oct 9, 2019 at 14:25 | comment | added | ralfcis | If you look at this video at 11:30 youtube.com/… , you will see relativity does not use a ruler to measure the moving length from a stationary perspective. It uses the relative simultaneity of clocks and does not measure the length of the pole but where its two endpoints are separated by perspective time. So if time keeps a permanent record then there is a permanent record of length. No need for metronomes or odometers to preserve the symmetry between time and space. | |
| Oct 9, 2019 at 2:53 | history | edited | Dale | CC BY-SA 4.0 |
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| Oct 8, 2019 at 19:02 | comment | added | Žarko Tomičić | Time dilation does not effect a thing that is moving. Because there is no absolute movement. | |
| Oct 8, 2019 at 17:35 | comment | added | Dale | @Albert a metronome is a frequency standard. It measures temporal intervals, $\Delta t$. A clock is a metronome plus a counter. It measures elapsed time $t=n \Delta t$. Similarly a ruler or rod measures spatial intervals, $\Delta x$. An odometer is a ruler plus a counter. It measures elapsed distance $x=n\Delta x$. Hence the similarity. Time dilation affects metronomes the same way that length contraction affects rulers. Time dilation affects clocks the same way that length contraction affects odometers. | |
| Oct 8, 2019 at 17:15 | comment | added | user139020 | „There is no permanent time dilation for a metronome “ Somehow it doesn't sound very good. Still, up to now I was 100% sure that time dilation affects everything, including metronomes. That lead me astray. It probably means, that if no one counts metronome's swings (does not maintain the record), or there is no counter attached, time dilation will not affect it. | |
| Oct 8, 2019 at 15:32 | comment | added | MCon | The relevant difference is metronome gives the tick, while a clock counts the ticks. In the paradox less ticks were counted because there have been a stretch of time when the "tick" was slower, but ticking resumes at the normal pace, but this doesn't change the (lower) count. Same difference between a meter and an odometer. | |
| Oct 8, 2019 at 14:46 | comment | added | user139020 | It is rather a ruler, he he he. | |
| Oct 8, 2019 at 14:39 | comment | added | user139020 | You (and the author) are 100% right. Of course, if the hands fell off the clock, generally speaking, it’s not quite a clock, It is not possible to know how much time dilation it has accumulated, it is impossible to measure time interval. Mentally, I could not get rid of the dial. | |
| Oct 8, 2019 at 14:16 | comment | added | OrangeDog | @Albert a metronome is not a clock. If you put a counter on it then it becomes a clock and is no longer a metronome. | |
| Oct 8, 2019 at 13:19 | comment | added | user139020 | The clocks maintain a permanent record of their dilation. Metronomes have no capacity for this. Sure, somehow I unintentionally have attached counter to metronome and stuck on it. | |
| Oct 8, 2019 at 13:10 | comment | added | Dast | The point is that the twin who travelled and then came back does not spend the rest of their life moving in slow motion, or any flatter. They now move at ordinary speed (although are younger than they should be). In a similar way they are ordinary in shape (no space compression) but the total distance they have travelled (according to a machine they brought with them on their space voyage) is a lot less than the total distance that you would have thought it was to their destination and back. | |
| Oct 8, 2019 at 13:09 | comment | added | HTNW | @Albert Because the clock tells you the time. If you took two clocks that both read 12:00 and sent one on a relativistic trip before bringing it back to rest, you could end up with, say, 12:05 and 12:10. This 5 minute difference will never vanish. The clocks maintain a permanent record of their dilation. Metronomes have no capacity for this. | |
| Oct 8, 2019 at 13:01 | comment | added | user139020 | Hmm... If you set off a metronome at one tick per second and then move it at close to C then the ticking with slow down .... But when you bring it back to relative resting it will still be ticking at 1 tick per second. This is perfectly correct also for Big Ben. Whereas the clock in the paradox is measuring the time interval from leaving to returning I believe, this is also correct for metronome. How are metronome clicks different from ticking of any other clock? There is no permanent time dilation for a metronome What does it mean,for a metronome? | |
| Oct 8, 2019 at 12:12 | comment | added | Fogmeister | @Albert I believe what is being said is that the ruler measures the distance between two points in space just as the metronome measures the “distance” between points in time. If you set off a metronome at one tick per second and then move it at close to C then the ticking with slow down. Just as the ruler will contract. But when you bring it back to relative resting it will still be ticking at 1 tick per second. Whereas the clock in the paradox is measuring the time interval from leaving to returning. Just as the odometer is measuring the perceived distance travelled from leaving to returning. | |
| Oct 8, 2019 at 12:00 | comment | added | user139020 | "The device that most closely resembles a ruler for time is not a clock but rather a metronome. There is no permanent time dilation for a metronome, in this way it is symmetric with the impermanence of length contraction." Could you please to clarify: why metronomes rise above other clocks? Do you mean, that metronome (and attached to him counter) would not accumulate time dilation, if moved to a distant point and back? | |
| Oct 8, 2019 at 2:12 | history | answered | Dale | CC BY-SA 4.0 |