Travelling at the speed of light?

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It may be possible [project Starshot] to accelerate very tiny probes to about 20% the speed of light, allowing them to zip by the Centauri stars/exoplanets in about 21 years.

If we could reach speeds near the speed of light we can go great distances due to time dilation. But the energy needed for this is way beyond our abilities.

If we could travel at, say, 78% the speed of light, we would get to Proxima Centauri in 7.8 years, but this ignores a few years for accelaration/decceleration. The extra energy needed for this is about 2x the normal energy since the travelers/ship would have about double the relativistic mass.
I have never understood the relativistic mass thing. Does that mean you weigh twice as much as you did on a starship on a weight scale as you would on Earth? The whole thing is going faster but why does that mean it weighs more?
 

Catastrophe

"There never was a good war, or a bad peace."
MM, the faster you go, talking near light speeds, the more you weigh (the greater your mass. This is one reason that going at light speed is not possible. The faster you go the greater the mass of you and your spacecraft and thus the more fuel you need to move the extra mass. And the greater the mass of the fuel you have.

Nothing can travel faster than 300,000 kilometers per second (186,000 miles per second). Only massless particles, including photons, which make up light, can travel at that speed. It's impossible to accelerate any material object up to the speed of light because it would take an infinite amount of energy to do so.
Cosmic Speed Limit | AMNH
https://www.amnh.org › exhibitions › einstein › light › co...


The cosmic speed limit: Why can't we travel at light speed?
https://www.scienceworld.ca › stories › cosmic-speed-li...



8 Jul 2015 — According to the laws of physics, as we approach light speed, we have to provide more and more energy to make an object move. In order to reach ...

Cat :)
 
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I have never understood the relativistic mass thing. Does that mean you weigh twice as much as you did on a starship on a weight scale as you would on Earth? The whole thing is going faster but why does that mean it weighs more?
Cat has a great answer, but keep in mind that those on the ship would not notice any unusual weight change.

IMO, it really helps to understand that Einstein wanted to call his theory the Invariance theory because nothing changes for one's own frame of reference (inertial frame). Thus, thanks to him, the laws of physics don't have to get funky to address all the motions in the universe.

A tiny mass traveling near the speed of light will have far more KE than the simple Newtonian equation of KE = 1/2 (mv^2), but this becomes important only when it impacts something that is "standing still" or going "slow".
 
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Catastrophe

"There never was a good war, or a bad peace."
KE = kinetic energy. Something you don't want hitting you if it is large in number.

A bullet travelling at 1,000 mph is much more dangerous than the bullet falling from 2 feet.

Cat :)
 
KE = kinetic energy. Something you don't want hitting you if it is large in number.

A bullet travelling at 1,000 mph is much more dangerous than the bullet falling from 2 feet.
Those hypersonic missiles almost don't need explosives as they are traveling > Mach 5.

There are long range sport rifles where the bullets travel at almost Mach 5, allowing for hitting targets more than 1 mile distance, if it's not too windy. :)
 

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