10 ms·

I know this is true, but I never got my head around this, maybe someone can help. So if a photon is emitted from the sun, it's passing earth immediately? Then w

by yawaworht1978 5y ago

I know this is true, but I never got my head around this, maybe someone can help. So if a photon is emitted from the sun, it's passing earth immediately? Then why does sunlight need 7 or 8 minutes to get to earth? And let's say, i travel one light-year at the speed of light, that should be instantaneous, right? The odometer would show 1 light-year, my watch would should 0 seconds and some decimals. How much would I have aged by the end of the journey? If I travelled at one percent of speed of light, same distance, i suppose 100 years would elapse for me, how much would elapse on earth? Odometer would still show one light year? And what if I left earth at 50percent of light speed , traveled 1 light-year away and did a turn and came back to earth at same speed. For me, it would be 1 year, but if I had a twin brother who was waiting on earth, would i now be a year younger than him? And how is this possible?

nycdatasci 5y ago
Einstein can help: https://books.google.com/books/download/Relativity.pdf?id=3H46AAAAMAAJ&output=pdf https://books.google.com/books/download/Relativity.pdf?id=3H... His book was intended to help people understand these exact questions, without getting into any complex math. Regarding "how is this possible?": This was experimentally verified in the 70s in the Hafele–Keating Experiment. Read more here: https://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment https://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experim...
- hollander 5y ago
  That Google link doesn't work. https://www.gutenberg.org/ebooks/5001 https://www.gutenberg.org/ebooks/5001
  - nycdatasci 5y ago
    Thanks!
justusthane 5y ago
> So if a photon is emitted from the sun, it's passing earth immediately? Then why does sunlight need 7 or 8 minutes to get to earth? From the photon's perspective, it passes earth immediately. From our perspective, it takes 7 or 8 minutes. > And let's say, i travel one light-year at the speed of light, that should be instantaneous, right? The odometer would show 1 light-year, my watch would should 0 seconds and some decimals. How much would I have aged by the end of the journey? You would have aged as much as your watch says you would have aged. Zero seconds. >If I travelled at one percent of speed of light, same distance, i suppose 100 years would elapse for me, how much would elapse on earth? I don't know how to do the math, but a very, very long time would have passed on earth. > And what if I left earth at 50percent of light speed , traveled 1 light-year away and did a turn and came back to earth at same speed. For me, it would be 1 year, but if I had a twin brother who was waiting on earth, would i now be a year younger than him? And how is this possible? Yes, you would be younger than him, and it's possible because that's just how relativity and time dilation work. It's even practically measurable in "real" life: http://www.leapsecond.com/great2005/tour/ http://www.leapsecond.com/great2005/tour/
- throw_away 5y ago
  > > If I travelled at one percent of speed of light, same distance, i suppose 100 years would elapse for me, how much would elapse on earth? > I don't know how to do the math, but a very, very long time would have passed on earth. Eh, at .01c, not so much: https://www.omnicalculator.com/physics/time-dilation?c=USD&v=equation:0,t:100!yrs,v:3000!kmps https://www.omnicalculator.com/physics/time-dilation?c=USD&v... (=100.005y, not even two days extra)
  - wruza 5y ago
    Yeah, all interesting things only begin at roughly 0.5c and go crazy at 0.9c. Google images on “lorentz factor” to get the quick idea. https://www.google.ru/search?q=lorentz+factor&tbm=isch https://www.google.ru/search?q=lorentz+factor&tbm=isch
    - deleted 5y ago
      [deleted]
danielsju6 5y ago
If you were watching their lives out the window of your spaceship you’d see them in fast forward vv. they’d see you in slow motion. Everything is relative. The main ”paradox” found by experimention is that the speed of light is a constant, regardless of your velocity. The only way this could be true, if you do a thought experiment, is if time was dialating for you. As for the physical and mathematical “why is this happening”, that’s where Einstein comes in. It’s an exponential. At 0.5c 100 years to you would be 115 years elasped to an observer, 0.9c 229 years, 0.999c 2,236 years, etc. Here’s an online calculator for the dilation effect https://www.omnicalculator.com/physics/time-dilation https://www.omnicalculator.com/physics/time-dilation
- lurquer 5y ago
  > If you were watching their lives out the window of your spaceship you’d see them in fast forward vv. they’d see you in slow motion. Everything is relative. Both observers, looking at one another, would see the other moving near c. Neither would know who was ‘actually’ moving. Yet, you assume there would not be a symmetry in their respective views of the other’s passage of time. Explain why. In simpler terms, a twin in a c-speed rocket could very well assume he was still and the earth was moving away. He should expect to find a younger twin when the earth ‘returned.’ Yet the examples only have the earth twin age, so to speak, and not the rocket twin.
  - deleted 5y ago
    [deleted]
  - jeffwass 5y ago
    The symmetry is broken in your twin example because the travelling twin had to accelerate to depart, accelerate to turn around, and accelerate to stop again at earth.
    - platz 5y ago
      It has nothing to do with acceleration. You can play games with acceleration and start to get "wrong" answers with the twin paradox. What actually matters is who travels the longest World Line a.k.a. the longest path in 4-d spacetime https://en.wikipedia.org/wiki/World_line https://en.wikipedia.org/wiki/World_line . That is all. A person on a non-curved geodesic spacetime path ages more quickly than a person on a curved non-geodesic spacetime path
deleted 5y ago
[deleted]
chrischen 5y ago
> And let's say, i travel one light-year at the speed of light, that should be instantaneous, right? Time slows down for the faster moving particles. And by time slowing down we mean all the particles in your body equally all start to move slower and more sluggishly in sync. This is because it takes more energy to accelerate a particle as it approaches the speed of light. So if you had a pendulum clock moving almost at the speed of slight, that velocity of the pendulum at rest would be at X m/s, but if the whole system is already moving super fast the extra X m/s would take too much energy. So since the energy is constant the relative speed of the pendulum just becomes much slower.
- thoughtstheseus 5y ago
  This is a superb description.
asdfge4drg 5y ago
because light doesn't experience time, and the closer you get to the speed of light, the less time you experience. So what OP didn't say was that, while YOU can travel many lightyears in your lifetime, everyone you know will long be dead.

nycdatasci 5y ago

Einstein can help: https://books.google.com/books/download/Relativity.pdf?id=3H46AAAAMAAJ&output=pdf https://books.google.com/books/download/Relativity.pdf?id=3H... His book was intended to help people understand these exact questions, without getting into any complex math. Regarding "how is this possible?": This was experimentally verified in the 70s in the Hafele–Keating Experiment. Read more here: https://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment https://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experim...

hollander 5y ago
That Google link doesn't work. https://www.gutenberg.org/ebooks/5001 https://www.gutenberg.org/ebooks/5001
- nycdatasci 5y ago
  Thanks!

justusthane 5y ago

> So if a photon is emitted from the sun, it's passing earth immediately? Then why does sunlight need 7 or 8 minutes to get to earth? From the photon's perspective, it passes earth immediately. From our perspective, it takes 7 or 8 minutes. > And let's say, i travel one light-year at the speed of light, that should be instantaneous, right? The odometer would show 1 light-year, my watch would should 0 seconds and some decimals. How much would I have aged by the end of the journey? You would have aged as much as your watch says you would have aged. Zero seconds. >If I travelled at one percent of speed of light, same distance, i suppose 100 years would elapse for me, how much would elapse on earth? I don't know how to do the math, but a very, very long time would have passed on earth. > And what if I left earth at 50percent of light speed , traveled 1 light-year away and did a turn and came back to earth at same speed. For me, it would be 1 year, but if I had a twin brother who was waiting on earth, would i now be a year younger than him? And how is this possible? Yes, you would be younger than him, and it's possible because that's just how relativity and time dilation work. It's even practically measurable in "real" life: http://www.leapsecond.com/great2005/tour/ http://www.leapsecond.com/great2005/tour/

throw_away 5y ago
> > If I travelled at one percent of speed of light, same distance, i suppose 100 years would elapse for me, how much would elapse on earth? > I don't know how to do the math, but a very, very long time would have passed on earth. Eh, at .01c, not so much: https://www.omnicalculator.com/physics/time-dilation?c=USD&v=equation:0,t:100!yrs,v:3000!kmps https://www.omnicalculator.com/physics/time-dilation?c=USD&v... (=100.005y, not even two days extra)
- wruza 5y ago
  Yeah, all interesting things only begin at roughly 0.5c and go crazy at 0.9c. Google images on “lorentz factor” to get the quick idea. https://www.google.ru/search?q=lorentz+factor&tbm=isch https://www.google.ru/search?q=lorentz+factor&tbm=isch
  - deleted 5y ago
    [deleted]

danielsju6 5y ago

If you were watching their lives out the window of your spaceship you’d see them in fast forward vv. they’d see you in slow motion. Everything is relative. The main ”paradox” found by experimention is that the speed of light is a constant, regardless of your velocity. The only way this could be true, if you do a thought experiment, is if time was dialating for you. As for the physical and mathematical “why is this happening”, that’s where Einstein comes in. It’s an exponential. At 0.5c 100 years to you would be 115 years elasped to an observer, 0.9c 229 years, 0.999c 2,236 years, etc. Here’s an online calculator for the dilation effect https://www.omnicalculator.com/physics/time-dilation https://www.omnicalculator.com/physics/time-dilation

lurquer 5y ago
> If you were watching their lives out the window of your spaceship you’d see them in fast forward vv. they’d see you in slow motion. Everything is relative. Both observers, looking at one another, would see the other moving near c. Neither would know who was ‘actually’ moving. Yet, you assume there would not be a symmetry in their respective views of the other’s passage of time. Explain why. In simpler terms, a twin in a c-speed rocket could very well assume he was still and the earth was moving away. He should expect to find a younger twin when the earth ‘returned.’ Yet the examples only have the earth twin age, so to speak, and not the rocket twin.
- deleted 5y ago
  [deleted]
- jeffwass 5y ago
  The symmetry is broken in your twin example because the travelling twin had to accelerate to depart, accelerate to turn around, and accelerate to stop again at earth.
  - platz 5y ago
    It has nothing to do with acceleration. You can play games with acceleration and start to get "wrong" answers with the twin paradox. What actually matters is who travels the longest World Line a.k.a. the longest path in 4-d spacetime https://en.wikipedia.org/wiki/World_line https://en.wikipedia.org/wiki/World_line . That is all. A person on a non-curved geodesic spacetime path ages more quickly than a person on a curved non-geodesic spacetime path

deleted 5y ago

[deleted]

chrischen 5y ago

> And let's say, i travel one light-year at the speed of light, that should be instantaneous, right? Time slows down for the faster moving particles. And by time slowing down we mean all the particles in your body equally all start to move slower and more sluggishly in sync. This is because it takes more energy to accelerate a particle as it approaches the speed of light. So if you had a pendulum clock moving almost at the speed of slight, that velocity of the pendulum at rest would be at X m/s, but if the whole system is already moving super fast the extra X m/s would take too much energy. So since the energy is constant the relative speed of the pendulum just becomes much slower.

thoughtstheseus 5y ago
This is a superb description.

asdfge4drg 5y ago

because light doesn't experience time, and the closer you get to the speed of light, the less time you experience. So what OP didn't say was that, while YOU can travel many lightyears in your lifetime, everyone you know will long be dead.