Objects near the speed of light

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Discussion Overview

The discussion revolves around the relativistic effects experienced by an object moving at nearly the speed of light, particularly focusing on how observers on Earth perceive such an object and the implications of time dilation for both the observers and the occupants of the object.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that an object moving at nearly the speed of light would appear motionless to observers on Earth, prompting questions about the nature of this perception.
  • Another participant challenges this view, stating that the ship would be seen approaching at nearly the speed of light, not appearing motionless.
  • There is a discussion about time dilation, with some participants asserting that time would appear to slow down for the occupants of the ship while remaining normal for Earth observers.
  • A participant seeks clarification on the relationship between the time experienced by an observer on Earth and that experienced by someone inside the ship, referencing the time dilation formula from special relativity.
  • One participant provides an example involving a bouncing ball to illustrate the concept of proper time and how it relates to the time measured by an observer on Earth.
  • Confusion arises regarding the implications of time dilation on the perceived motion of the ship, with a participant expressing gratitude for the clarification provided by others.

Areas of Agreement / Disagreement

Participants express disagreement regarding the initial claim that the ship would appear motionless to Earth observers. Multiple competing views remain about how the ship's motion and time dilation are perceived by different observers.

Contextual Notes

Participants reference the time dilation formula and its implications, indicating a need for clarity on how relativistic effects manifest in different frames of reference. There is an acknowledgment of confusion surrounding these concepts.

really?
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Hi,

i'm new to this and maybe this has been covered but-

Imagine an object moving at almost the speed of light, is on a collision course with earth. To observers on Earth the ship seems to be motionless, due to it's speed being extremely close to c.

Eventually the ship is going to be very close to earth, let's say, that to an Earth observer it seems to be hovering about 1m from the Earth's surface.

What would happen to someone or something which touched this ship?
Would they be instantly propelled into the ships frame of reference or would they be able come and go as they please?

I hope that made some sort of sense... any thoughts would be much appreciated...

Thanks
 
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really? said:
To observers on Earth the ship seems to be motionless, due to it's speed being extremely close to c.
That is incorrect.
 
cesiumfrog said:
That is incorrect.

incorrect how? could you please direct me to something which will explain how an observer on Earth would see the ship.

i came to believe that it was a consequence of time dialation
 
Imagine a stopped clock being thrown at you: they won't see the occupants moving very quickly inside the ship, but they will see the entire ship (and everything inside) approaching at nearly the speed of light. It will hit the Earth very quickly (with little notice).
 
cesiumfrog said:
Imagine a stopped clock being thrown at you: they won't see the occupants moving very quickly inside the ship, but they will see the entire ship (and everything inside) approaching at nearly the speed of light. It will hit the Earth very quickly (with little notice).

i don't understand what your trying to say...
are you saying that the observers on Earth would see the ship approaching at nearly the speed of light and not time dialted to a point where it appears motionless?

i forgot to mention that the ship is moving at nearly the speed of light relative to the observers of the earth
 
really? said:
i don't understand what your trying to say...
are you saying that the observers on Earth would see the ship approaching at nearly the speed of light and not time dialted to a point where it appears motionless?
That is correct, it won't. As Cesium frog said, time will 'slow down' for the people inside the ship, but will be running at 'normal' time for you. Time will appear dilated for the crew but not for you.
 
Last edited:
Hootenanny said:
That is correct, it won't. As Cesium frog said, time will 'slow down' for the people inside the ship, but will be running at 'normal' time for you. Time will appear dilated for the crew but no for you.

okay, so what would be the relationship between my time and the time in the ship? in other words if i could see a clock in the ship at what speed is it running and vice versa?

i'm trying to make sense of the time dialtion formula in special relativity that i found on wikipedia, maybethat was my first mistake?
 
Okay, say someone on this ship (travelling towards you at v m/s) was bouncing a ball. Another crew member timed the interval between two bounces. This would be the proper time interval ([itex]\Delta t_{0}[/itex]). Now, if you timed the same interval on Earth you would measure the time interval as [itex]\Delta t[/itex], such that;

[tex]\Delta t = \gamma \Delta t_{0} = \frac{\Delta t_{0}}{\sqrt{1-\beta^2}}\hspace{1cm}\beta = \frac{v}{c}<1[/tex]
 
running very slowly, but nonetheless moving towards you very quickly.
 
  • #10
cesiumfrog said:
running very slowly, but nonetheless moving towards you very quickly.

i think that is where i was getting confused... i thought that since the clock was running slowly then the whole ship would seem to be moving slowly...

thank you both for clearing that up...

cheers
 

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