To Saturn at (nearly) the speed of light

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SUMMARY

This discussion centers on the implications of traveling to Saturn at near-light speed, specifically addressing the effects of relativity on time perception for both the traveler and observers on Earth. When a rocket travels at approximately 186,000 miles per second, it takes about an hour for the rocket to reach Saturn, as perceived from Earth. The concept of time dilation is clarified, indicating that while the onboard clock may register significantly less time, it does not imply that the rocket travels faster than light. The conversation also touches on the twin paradox, emphasizing that both time and distance are perceived differently by moving observers compared to stationary ones.

PREREQUISITES
  • Understanding of special relativity principles
  • Familiarity with time dilation and length contraction
  • Basic knowledge of the twin paradox scenario
  • Awareness of astronomical distances, specifically between Earth and Saturn
NEXT STEPS
  • Research the twin paradox in detail to understand its implications on time perception
  • Explore the concept of time dilation as described by Einstein's theory of relativity
  • Investigate the effects of traveling at relativistic speeds on physical objects
  • Learn about the practical challenges of achieving near-light-speed travel
USEFUL FOR

Astronomy enthusiasts, physics students, and anyone interested in the implications of relativity on space travel and time perception.

  • #61
.Scott said:
There may be parts of the universe that are either behind an event horizon or would move behind that horizon before you reached them.

Moving behind an event horizon doesn't make them unreachable to us; it just makes us unreachable to them. The accelerating expansion of the universe (assuming that our current model of that is correct) makes things unreachable both ways, so to speak.
 
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  • #62
PeterDonis said:
Moving behind an event horizon doesn't make them unreachable to us; it just makes us unreachable to them. The accelerating expansion of the universe (assuming that our current model of that is correct) makes things unreachable both ways, so to speak.
Right. It works both ways. Our event horizon (as seen from them) keeps us from getting to them and their event horizon (as seen by us) keeps them from getting to us.
 
  • #63
.Scott said:
Right. It works both ways. Our event horizon (as seen from them) keeps us from getting to them and their event horizon (as seen by us) keeps them from getting to us.

This amounts to saying that we and they are each inside a black hole with respect to the other. That's not correct. The cosmological horizon involved here is not the same as a black hole's event horizon. For one thing, its location in space changes with time. For another, its location in spacetime (i.e., which surface in spacetime it is) is different for different observers. Neither of those things are true for a black hole's event horizon.
 
  • #64
PeterDonis said:
This amounts to saying that we and they are each inside a black hole with respect to the other. That's not correct. The cosmological horizon involved here is not the same as a black hole's event horizon. For one thing, its location in space changes with time. For another, its location in spacetime (i.e., which surface in spacetime it is) is different for different observers. Neither of those things are true for a black hole's event horizon.
There are several ways to create an event horizon. One is with a black hole. Another is with simple continuous acceleration. Another is with expansion of space.
They all have the same characteristics - extreme time dilation, Hawking radiation.

I wasn't saying anything about black holes.
 
  • #65
I think that any null surface can be considered an event horizon. Once you cross it you cannot send signals back to the other side.
 

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