The theoretical max. speed in deep space

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Discussion Overview

The discussion centers around the theoretical maximum speed of a spacecraft in deep space, particularly whether it can reach the speed of light. Participants explore concepts related to momentum, energy, and the effects of relativistic physics on acceleration.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that in deep space, the absence of friction allows for unlimited speed increase with added energy.
  • Others clarify that while momentum can be continuously added, the speed of light cannot be reached due to relativistic effects.
  • One participant questions the equivalence of accelerating from different speeds, suggesting that the change in momentum required is not the same at higher speeds.
  • Another participant emphasizes that as speed approaches the speed of light, the required force for further acceleration increases significantly.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between energy, momentum, and speed in deep space. There is no consensus on whether the theoretical maximum speed can be considered unlimited.

Contextual Notes

The discussion involves assumptions about the nature of momentum and energy in relativistic contexts, and the implications of these concepts on acceleration near the speed of light remain unresolved.

Faux Carnival
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Hello,

Isn't the theoretical max. speed in deep space unlimited? There is no friction. Therefore, any energy we add to the spacecraft will increase its speed. So can't the speed of light be reached?

Thanks.
 
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Hello Faux Carnival! :smile:
Faux Carnival said:
Isn't the theoretical max. speed in deep space unlimited? There is no friction. Therefore, any energy we add to the spacecraft will increase its speed. So can't the speed of light be reached?

(hmm … i thought pf had an faq on this, but i can't find it :confused:)

first, we add momentum, not energy (force times time = change in momentum) :wink:

second, yes we can keep adding momentum, and the speed will keep increasing :smile:, but it will never quite reach c :redface:

(momentum = mv/√(1 - v2/c2) -> ∞ as v -> c)
 
tiny-tim said:
Hello Faux Carnival! :smile:


(hmm … i thought pf had an faq on this, but i can't find it :confused:)

first, we add momentum, not energy (force times time = change in momentum) :wink:

second, yes we can keep adding momentum, and the speed will keep increasing :smile:, but it will never quite reach c :redface:

(momentum = mv/√(1 - v2/c2) -> ∞ as v -> c)


Thanks for your reply. I was thinking of kinetic energy. They seem to be the same thing anyway.

But my thinking is not flawed, right? In space, accelerating from 30,000 to 31,000 km/h is the same thing as accelerating from 50,000 to 51,000 km/h?
 
Faux Carnival said:
In space, accelerating from 30,000 to 31,000 km/h is the same thing as accelerating from 50,000 to 51,000 km/h?

Nope!

The latter involves slightly more change in momentum … mv/√(1 - v2/c2) … than the former.

And so the latter takes slightly more force (technically, impulse) than the former.

And the closer you get to the speed of light, the greater the difference! :smile:
 

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