PDA

View Full Version : Accelerating to light speed



Githyanki
2012-Jan-08, 12:48 AM
Accelerating to light speed.


How many light years are needed to accelerate towards near light speed in a space-craft that has humans on board?


You just can't instantly go light-speed like in Star Wars, with a human crew; the acceleration-forces would turn them into mush.

Say if we had the ability to travel at 99.9999% that of the speed of light and we wanted to go to Alpha Centauri. We have to spend a time period accelerating to the limits of human withstanding of G forces and then an equal time decelerating within the limits of human resistance to G-forces. I'm thinking we can't travel to AC3 going light speed because the distances are too short?

schlaugh
2012-Jan-08, 04:41 AM
I think this site will be useful:

http://www.ajdesigner.com/constantacceleration/cavelocity.php

Know that 1G = 10m/s so enter a starting veolcity of 0 and an acceleration of 10 meters per second for 365 days and you'll see you're moving faster than light at >315,000 kilometers per second. (The calculator does not care about relativisitic effects or E=MC^2).

Tensor
2012-Jan-08, 05:11 AM
Accelerating to light speed.


How many light years are needed to accelerate towards near light speed in a space-craft that has humans on board?

the answer is going to depend on exactly what you mean by near light speed. You specify below, but.....


You just can't instantly go light-speed like in Star Wars, with a human crew; the acceleration-forces would turn them into mush.

Say if we had the ability to travel at 99.9999% that of the speed of light and we wanted to go to Alpha Centauri. We have to spend a time period accelerating to the limits of human withstanding of G forces and then an equal time decelerating within the limits of human resistance to G-forces. I'm thinking we can't travel to AC3 going light speed because the distances are too short?

You're thinking correctly. The problem comes from relativity. Schlaugh give a site that will calculate for you. However, it does not take relativity into account. This site (http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html) by originally by Phillip Gibbs and hosted on John Baez's home site, gives the exact equations for the Time within the ship, the time for observers outside the ship, the distance traveled(as seen by outside observers), the velocity(by percentage of c), and the gamma factor(at any point). In the case of 99.9999%, at 1g, it would take ~1,839 years and a distance of ~1840 light years. So, getting to that speed is pretty much out if you're thinking of going to Alpha Centauri. That site has the equations, so you can figure out what would happen if you increased the acceleration to something like 2 or 3 g's. Which may be pushing the limits for human endurance over an extended time. Unfortunately, that site doesn't do an automatic calculation.

Githyanki
2012-Jan-08, 09:21 PM
That's what I figured. I guess we won't be having any express-flights to any of the local stars.

Now I'm assuming that a space probe can handle a lot more Gees than a human can. But there is still a limit of how much acceleration you can use before you damage your instruments.