# Monorail In Space

Discussion in 'Science and Technology' started by Into Darkness, May 25, 2014.

1. ### Into DarknessCaptainCaptain

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Mar 27, 2013
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Imagine we built a railway line in space, ok let's think more along the lines of a magnetic monorail. You have a start point and an end point. The start point and end point are 5 lightyears in distance.
You sit on a rail carriage on the mono-spacerail and it's powered by let's say a huge fusion reactor or maybe a solar dyson sphere around a star. Power is not a problem.
How fast theoretically could that carriage reach on that rail? would there even be a limit? would a point come as it got faster where it's mass increase would make it impossible to go any faster?

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Jul 2, 2009
Speed of light?

3. ### MetryqFleet CaptainFleet Captain

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Jan 23, 2013
I'm assuming the point of this hypothetical monorail (maglev?) is to remove the limitation of carrying fuel and paying its penalty mass. That is the point behind beamed energy starships, such as laser sails, and the Bussard ramjet.

Building a lightyears-long rail is absurd, but we'll take it in the spirit in which it was suggested. That makes the rail our new "medium." If we let the train ignore Einstein for now (gasp!) that makes the speed limit of the train the wave speed of the medium. Off hand, I do not know the speed of the impulse in a maglev rail, but it must be under the speed of light. (Electrons in a wire move at mere meters per hour, but the electric field outside the wire travels at close to the speed of light.)

Imagine that the train is a prop-driven plane in level flight. It can approach the speed of sound, but never exceed it. The plane's "mass" is not increasing, but the effect is the same as that described by Special Relativity for a starship approaching the speed of light. The plane is limited by the wave speed of the medium (the air). Now, if the plane had a jet engine...

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Very.

Yes.

No.

These answers are exactly as specific as the scenario. I could be more specific if I knew what the rail was made of and/or what the engine is.

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Assume the rail is made of pasta and the power source is hot marinara sauce.

6. ### MetryqFleet CaptainFleet Captain

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Jan 23, 2013
In that case, the speed approaching the table is much faster than the waddle away from the table (Urp!) due to increased mass.

7. ### Into DarknessCaptainCaptain

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Use whatever statistics for it you want. The rail can be made of adamantium for all I care, I just want to determine if there is a speed limit in space for a magnetically accelerated carriage (maglev).

You see with rockets you have the problem of carrying fuel and I imagine there's a limit to the amount of thrust can be produced because the engine would need to continually be made bigger.

So what I'm doing is trying to make the power source and propelling force external leaving just the carriage to travel to light speed.

So I want to know, if the power source could use as much juice as it needs and the maglev rail could generate a field as powerful as it needs to, does that carriage have a limit to how fast it can travel?

Could a carriage in space be propelled on a maglev style rail to the speed of light or nowhere near it?

8. ### Alidar JarokEverything in moderation but moderationModerator

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Norfolk, VA
This seems a good question for: What if XKCD

It seems, no matter what, there would be friction and energy costs (and costs to transport the energy over large distances). But it does at least deal with the problem of needing fuel to cover the cost of the fuel you're carrying. It just has other practical problems instead.

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Yes, the speed limit in space for magnetic railcars is 299,792,457 m/s. I don't know when the law was passed.

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10. ### RobertVAFleet CaptainFleet Captain

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Nearly 14 Billion years ago would be my guess

11. ### MetryqFleet CaptainFleet Captain

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Jan 23, 2013
Right. The universal speed of light limit was passed with the Big Bang miracle, conveniently suspended for Guth's inflation (a brief burst of dark energy no doubt), then immediately reinstated.

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I'm thinking that by the time your interstellar rail line is extended to a nearby star, your construction crew is already there so why bother sending a train down the line?

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