Effects of time dilation for near-speed-of-light travel

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Discussion Overview

The discussion revolves around the effects of time dilation as described by special relativity, particularly in the context of near-speed-of-light travel at a velocity of .6c. Participants explore the implications of time dilation on the perception of time for travelers in a spaceship compared to observers on Earth, including calculations related to travel time to distant galaxies and the reception of signals.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that at .6c, a traveler experiences time at a rate that is 20 percent slower than people on Earth, leading to claims about the relationship between spaceship and Earth seconds.
  • One participant questions whether a traveler would reach a galaxy 10 light years away in 8 spaceship years, while others argue that the travel time should be calculated as distance divided by speed, leading to a different conclusion.
  • There is a proposal that the first signal from the spaceship would be received on Earth after 18 years, based on the travel time and the time taken for light to return, although this is contested.
  • Another participant recalculates the travel time to be approximately 16.66 Earth years, resulting in a perceived journey of about 13.328 spaceship years due to time dilation.
  • Some participants emphasize the importance of understanding the perspective of each observer, noting that each sees the other's time as slowed down, which complicates the analysis of time experienced during travel.
  • There are inquiries about how to determine which observer's time is actually slowed and how kinetic energy relates to the perception of time passage.
  • Clarifications are made regarding the proper time experienced by each observer, with some asserting that both experience time at one second per second in their respective frames of reference.

Areas of Agreement / Disagreement

Participants do not reach a consensus on several points, particularly regarding the calculations of travel time and the implications of time dilation. Disagreements persist about the interpretation of time experienced by the traveler versus the observer on Earth.

Contextual Notes

Participants express uncertainty regarding the calculations and the implications of time dilation, highlighting the complexity of the topic and the need for careful consideration of different frames of reference.

Who May Find This Useful

This discussion may be of interest to those studying special relativity, time dilation, and the implications of high-speed travel in physics, as well as individuals curious about the mathematical relationships involved in these concepts.

  • #61
malawi_glenn said:
Why not just pick up a book about relativity and study it? I can recommend the book by Morin "Special Relativity: For the Enthusiastic Beginner" which is quite cheap.
Thanks for the reference, I'll check it out!
 
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  • #62
Ibix said:
Light speed is also approximately one foot per nanosecond.
Grace Hopper used to hand out nanoseconds at her lectures. (one foot wire segments). The one time I heard her speak, wire was too expensive and I picked up a salt packet of picoseconds instead. (Google says pepper. I remember salt. Go figure).
 
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  • #63
jbriggs444 said:
Grace Hopper used to hand out nanoseconds at her lectures. (one foot wire segments). The one time I heard her speak, wire was too expensive and I picked up a salt packet of picoseconds instead. (Google says pepper. I remember salt. Go figure).
Go to t=46m00s [for milliseconds... start at t=45m07s]



About Adm Hopper


https://en.wikipedia.org/wiki/Grace_Hopper
 
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  • #64
Chenkel said:
Why do some people write c = 1?
Because they're using units called "natural units" in which ##c = 1##.

Chenkel said:
Why do some people write c = 299792458 meters per second?
Because they're using SI units, in which ##c# is defined to have that value.

I'm not sure what the issue is with this. Surely the existence of multiple different systems of units is no mystery.

Chenkel said:
Does the 1 in the expression "c = 1" represent one light second per second?
It can. Or it can mean one meter per light-meter (meter of light travel time). Or it can mean one light year per year. The point is that the unit of distance and the unit of time are related by the time it takes light to travel the distance. That makes things much simpler mathematically (you don't have stray factors of ##c## all over the place and have to worry about whether you've gotten them all right) and makes spacetime diagrams easier (because the worldlines of light rays are 45 degree lines and the units on both the space and time axes are the same).
 
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  • #65
Chenkel said:
My last reply just talked about treating Lorentz factor as an infinite hyperreal, not sure if this can be done
No, it can't. There is no such thing as an inertial frame in which a photon is at rest.
 
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  • #66
malawi_glenn said:
Why not just pick up a book about relativity and study it? I can recommend the book by Morin "Special Relativity: For the Enthusiastic Beginner" which is quite cheap.

It is hard (impossible) to learn a new subject on a forum.
I got the book recently and I've been studying it, it's interesting so far and I think I'll learn a lot from it.

Thank you for the suggestion 🙂
 
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