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k.steven washington
consider this: a person traveling in a spaceship at .99 light speed would experience 1 day for for every year that passed on earth. Conversely, 1 year would pass for every day aboard the ship. If the destination of the ship is 4 light years away and the ship travels for 4 years, earth time, It would arrive at it's destination. On board the ship, only 4 days have passed, due to time dilation. This has to be true because the ship can only affect its passengers, relative to time...not time on earth. time remains "normal" here, a year still roughly equals 8760 hours. Therefore astronauts would only need minimal food and water, for a journey of that distance. they could literally go and return in a couple of weeks.
Robittybob1
It would be interesting to see if living things could be accelerated to this sort of velocity. What sort of G force can a human body take without killing the person? At that max G force how long would it take to get to .99 of light speed?
So you might find you'll need a month's supply of food just to get to terminal velocity. And another month's supply for slowing down again.
Robittybob1
From Wiki Answers "Assuming that it is indeed possible for a sole entity apart from light to travel at the speed of light, it would require an acceleration no greater then the maximum g-force a human can withstand. That being said, the average human can withstand safely a g-force of about 3g's. A trained human can withstand a g-force of about 6g's per say. So assuming this particular human is to travel at light speed, they would still need to maintain regular cycles such as eating, drinking and so on. That being said no more then 3g's is realistic. After doing calculations, using t= (v2-v1)/a, plugging "c" in for v2, 0 in for v1, and "3g" in for a, we find the time required to reach light speed is approximately 31 years. So to now answer the question, a human could travel at light speed by spending 31 years at an acceleration of "3g". Take into account however, that time will slow down for the person approaching the speed of light. If he was able to reach the speed of light it is theorized that time would stop all together. "

Read more: http://wiki.answers.com/Q/How_can_a_human_...t#ixzz1czzIFiyU
Robittybob1
One other site didn't seem to think it would take nearly as long:
View Full Version : How long would it take to accelerate a person to the speed of light without dying?
http://boards.straightdope.com/sdmb/archiv...p/t-203257.html
"Going by classical physics

Velocity = g * time where g is the acceleration constant.

In "weightless" space, a person would be continuously subjected to a force of one 'g' if the person were accelerated at 32 ft/sec2. Since this is equaivalent to Earth's gravity, the person would be subjected to no undue stress.

The speed of light is about 300,000 kilometers per second which equals 984,000,000 feet per second.

Since v=g*t then
t = v/g
t= 984.000.000/32
t= 30,700,000 which is roughly speaking one year ( 1 year is about 31.5 million seconds).

As someone else mentioned, it isn't as straightforward as this because as we approach light speed, relativistic changes occur.
Here is a website for calculating relativistic changes:
http://www.1728.com/reltivty.htm

So, uniformly accelerating a spaceship cannot be done with the same amount of force. At 50% the speed of light, the mass of the ship increases by 15%. At 90 % the speed of light, the ship's mass has increased by 229%. So, you would need to expend 2.29 times the amount of fuel to continue the accelleration at 32 fett/sec2. Eventually this would be very impractical because at 99% light speed, the ship's mass has increased seven-fold.

So, let's suppose we have a ship that has enough fuel to account for the relativistic changes in mass, then the answer would be about a year IF you wanted to go at 99% light speed (your mileage may vary).

To tell you the truth that surprises me. I thought it might take a century or more so it is practical in terms of a person's lifetime. However, constructing a spaceship that could accelerate at 32 feet/sec2 would be impossible by today's technology. Among other things it would require enough fuel to burn continuously to maintain a one 'g' acceleration for one full year.

One more thing how far would you have travelled by the time you reach 99% light speed? IF you headed in a straight line, you would be 2.8 TRILLION MILES from where you started. This is roughly one half of a light year so this seems about right."
boit
The mass of the spaceship increases, the mass of fuel too increases. Doesn't that solve the fuel problem? It doesn't. Do you know why? I was told. Find the answer in this forum.
Robittybob1
QUOTE (boit+Nov 7 2011, 04:08 PM)
The mass of the spaceship increases, the mass of fuel too increases. Doesn't that solve the fuel problem? It doesn't. Do you know why? I was told. Find the answer in this forum.

Yep, you can solve the fuel problem but what about the Astronauts, how much food do they need to take on the 2 week round trip, that will take years????
k.steven washington
to boit, no i don't think that the increased fuel mass of the fuel solves the problem because remember everything on the ship increases mass.. including the engines and all of its parts...whatever ingests and processes the fuel, its appetite has also increased by whatever the mass ratio is , that affects everything else. So, the engines will run no longer than they would have run, prior to the increase in mass. Does that make sense to you?
k.steven washington
suppose you could accelerate to .99 light in about an hour, Earth time. Forget about the inertial effects...maybe we could "shift" the inertia away from the ship by compressing space ahead of the craft and extending it behind the craft. Somehow we nullify inertia. Now just dealing with time dilation, at .99 light speed, 1 day on board ship= 1 year, Earth time. If so, then, if the ship travels for 4 Earth years, then 4 days have passed on the ship. After traveling at that velocity for 4 Earth years the ship would be approaching Alpha Centauri. Only 4 days have elapsed on board ship. I guess the question I have is : does the motion of the occupants slow down relative to themselves.. are they moving in slow motion? To them, are they moving around at normal speed? If 1 day to them= 1 year on Earth, just walking across the cabin of the ship might take a month, Earth time. If time on board ship is perceived by those on board, to be moving at normal speed, and all their physical actions are perceived to be occuring at normal speed, Then they would not need much , in the way of provisions, to last during the journey because the trip would only last about 4 days, assuming their destination was roughly 4 light years away(Alpha).
k.steven washington
to robittybob1, you brought up an interesting notion about time stopping, if you achieved light speed. I wonder, would time run backward, if you moved past light speed?
Robittybob1
QUOTE (k.steven washington+Nov 8 2011, 05:52 AM)
to robittybob1, you brought up an interesting notion about time stopping, if you achieved light speed. I wonder, would time run backward, if you moved past light speed?

Maybe you could look back at yourself and see yourself getting younger but you would not be able to see yourself as you are.
Yet on reflection your past may not catch up with you.
Robittybob1
QUOTE (k.steven washington+Nov 8 2011, 05:38 AM)
suppose you could accelerate to .99 light in about an hour, Earth time. Forget about the inertial effects...maybe we could "shift" the inertia away from the ship by compressing space ahead of the craft and extending it behind the craft. Somehow we nullify inertia. Now just dealing with time dilation, at .99 light speed, 1 day on board ship= 1 year, Earth time. If so, then, if the ship travels for 4 Earth years, then 4 days have passed on the ship. After traveling at that velocity for 4 Earth years the ship would be approaching Alpha Centauri. Only 4 days have elapsed on board ship. I guess the question I have is : does the motion of the occupants slow down relative to themselves.. are they moving in slow motion? To them, are they moving around at normal speed? If 1 day to them= 1 year on Earth, just walking across the cabin of the ship might take a month, Earth time. If time on board ship is perceived by those on board, to be moving at normal speed, and all their physical actions are perceived to be occurring at normal speed, Then they would not need much , in the way of provisions, to last during the journey because the trip would only last about 4 days, assuming their destination was roughly 4 light years away(Alpha).

Most people could go without food for a couple of days, so don't worry about the food. Reaction time could be a real issue. Even at normal living the slowness of reaction time causes accidents to be unavoidable. So imagine if it takes a moth to walk across the cabin to flick a switch to put out the landing gear, and you're a little slow you find you have gone a million miles past your destination.
gocrew
QUOTE (k.steven washington+Nov 7 2011, 06:46 AM)
consider this: a person traveling in a spaceship at .99 light speed would experience 1 day for for every year that passed on earth.

The time dilation factor for something moving at .99c relative to another frame of reference is available at wikipedia, and probably a lot of other places on the web. It's about 7. Which means you are way off.
brucep
QUOTE (gocrew+Nov 10 2011, 10:50 PM)
The time dilation factor for something moving at .99c relative to another frame of reference is available at wikipedia, and probably a lot of other places on the web. It's about 7. Which means you are way off.


dTau_rocket = 1 day

dt_earth = ~ 7 day

v = .99

dTau_rocket/dt_earth = (1-v^2)^1/2 = (1-.99^2)^1/2 = .1410674

For every 1 tick in the earth coordinate frame there is 7.08881 ticks in the rocket proper frame.

For every day that passes in the rocket frame 7.08881 days pass in the earth [laboratory] frame.

brucep
QUOTE (brucep+Nov 11 2011, 09:05 PM)

dTau_rocket = 1 day

dt_earth = ~ 7 day

v = .99

dTau_rocket/dt_earth = (1-v^2)^1/2 = (1-.99^2)^1/2 = .1410674

For every 1 tick in the earth coordinate frame there is 7.08881 ticks in the rocket proper frame.

For every day that passes in the rocket frame 7.08881 days pass in the earth [laboratory] frame.

That was messed up. It should read

For every one tick in the rocket proper frame there is 7.0881 ticks in the earth coordinate frame [laboratory frame].
Robittybob1
QUOTE (brucep+Nov 12 2011, 07:36 AM)
That was messed up. It should read

For every one tick in the rocket proper frame there is 7.0881 ticks in the earth coordinate frame [laboratory frame].

Thanks for that.
boit
QUOTE (k.steven washington+Nov 8 2011, 07:52 AM)
to boit, no i don't think that the increased fuel mass of the fuel solves the problem because remember everything on the ship increases mass.. including the engines and all of its parts...whatever ingests and processes the fuel, its appetite has also increased by whatever the mass ratio is , that affects everything else. So, the engines will run no longer than they would have run, prior to the increase in mass. Does that make sense to you?

Yes. It makes perfect sense to me. To elaborate it is the measured (relativistic) mass that increases, not the actual mass. As in the spaceship won't suddenly develop high gravitational energy to pull objects it passes by when it is moving at say 99.9999999999% light speed. See?
boit
QUOTE (k.steven washington+Nov 8 2011, 08:38 AM)
suppose you could accelerate to .99 light in about an hour, Earth time. Forget about the inertial effects...maybe we could "shift" the inertia away from the ship by compressing space ahead of the craft and extending it behind the craft. Somehow we nullify inertia. Now just dealing with time dilation, at .99 light speed, 1 day on board ship= 1 year, Earth time. If so, then, if the ship travels for 4 Earth years, then 4 days have passed on the ship. After traveling at that velocity for 4 Earth years the ship would be approaching Alpha Centauri. Only 4 days have elapsed on board ship. I guess the question I have is : does the motion of the occupants slow down relative to themselves.. are they moving in slow motion? To them, are they moving around at normal speed? If 1 day to them= 1 year on Earth, just walking across the cabin of the ship might take a month, Earth time. If time on board ship is perceived by those on board, to be moving at normal speed, and all their physical actions are perceived to be occuring at normal speed, Then they would not need much , in the way of provisions, to last during the journey because the trip would only last about 4 days, assuming their destination was roughly 4 light years away(Alpha).

This shifting of space 'fore and aft, is it the idea behind SpaceDrive (the theoretical means of reactionless propulsion).
Robittybob1
QUOTE (boit+Nov 12 2011, 12:03 PM)
Yes. It makes perfect sense to me. To elaborate it is the measured (relativistic) mass that increases, not the actual mass. As in the spaceship won't suddenly develop high gravitational energy to pull objects it passes by when it is moving at say 99.9999999999% light speed. See?

There are so many statements made that light is affected by gravity due to it's relativistic mass, so why not the rocket? Can you give me a reference to justify your statement please?
Guest
I just bumped into this thread looking for a g-force question.
I think people missed the concept of time dilation. It is relative to frame of reference. For people on ship earth is moving at speed of light so 1 year on ship will be one day on earth. Similarly for a observer in middle both are moving at c/2 and showing sign of partial time dilation.
Thanks
Fridge2108
Just read about Alcubierre's Warp Drive. In the initial seconds of the universes existence it is thought that it expanded faster than the speed of light. I believe Alcubierre's Warp Drive is a bubble of negative energy (very tricky to find a supplier) that does the same thing. Essentially surround a ship with this bubble of negative energy and have it expand at the front and contract at the back faster than the speed of light, just like the early universe.
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