Originally posted by sonhouseAccording to the theory the same. In your instantaneous inertial frame you are stationary, everything else is moving towards you at 0.9c (on average).
Can anyone here answer a question in relativistic acceleration? My question is this: You have a space craft, from zero relative velocity, it starts accelerating at 1 standard g, 9.8 meters per second per second, and so forth.
If relativity was not a factor, it would reach the speed of light in about one year of such acceleration.
My question is, if at ...[text shortened]... ad a scale, would you still weigh 100 Kg like you did at the start or would it be different now?
Originally posted by DeepThoughtNot sure where you get the heating up thing, but if you had a thruster that put out 1 g of thrust at low velocities, wouldn't the given thrust at .9c mean that the actual g force would be less than half what it was at non relativistic velocity and therefore your weight would be noticeably less, 2.3X less, where now I weigh 43 Kg instead of 100 which is what my scale showed me when first we started the engines? Wouldn't that mean the actual g force would approach zero as the ship gets closer to c? Given a constant thrust of X newtons?
According to the theory the same. In your instantaneous inertial frame you are stationary, everything else is moving towards you at 0.9c (on average).
The problem is the interstellar medium is length contracted so it appears more dense on board, at 0.9c the gamma factor is 2.3 (you have to multiply this by the density in your initial frame, there is ...[text shortened]... t would create drag, causing your acceleration to drop and your rockets hull to heat up (a lot).
Originally posted by sonhouseNo, you've missed the point. Say you start out with zero speed relative to the sun, then by time you are moving at 0.9c in your own instantaneous reference frame you are stationary and the sun is moving away from you at 0.9c. So you will still be accelerating at 1g. An observer stationary w.r.t. the sun will think your acceleration has reduced, but they are in a different reference frame.
Not sure where you get the heating up thing, but if you had a thruster that put out 1 g of thrust at low velocities, wouldn't the given thrust at .9c mean that the actual g force would be less than half what it was at non relativistic velocity and therefore your weight would be noticeably less, 2.3X less, where now I weigh 43 Kg instead of 100 which is what ...[text shortened]... g force would approach zero as the ship gets closer to c? Given a constant thrust of X newtons?
Originally posted by DeepThoughtBut the effect of that acceleration is to not increase velocity at the same rate, right? If I am producing, say 1000 tons of thrust at zero velocity and 1000 tons of thrust at 0.9c, then that thrust is pushing against 2+ times the mass, wouldn't that result in a slower increase in velocity?
No, you've missed the point. Say you start out with zero speed relative to the sun, then by time you are moving at 0.9c in your own instantaneous reference frame you are stationary and the sun is moving away from you at 0.9c. So you will still be accelerating at 1g. An observer stationary w.r.t. the sun will think your acceleration has reduced, but they are in a different reference frame.
Originally posted by sonhouseThis is frame dependent. We need three observers, You in the spaceship, me in a space station which we'll assume is stationary, and one other moving away from me at a constant 0.9 c. Initially you and I are stationary with respect to each other. You switch on your boosters and accelerate away at 1 g. I stay put. As you get to 0.9 c relative to me you will for an instant be stationary with respect to the Third Man. At that moment you and the third man will agree that your acceleration is 1 g. I will think it is less - relative to me you cannot accelerate past the speed of light.
But the effect of that acceleration is to not increase velocity at the same rate, right? If I am producing, say 1000 tons of thrust at zero velocity and 1000 tons of thrust at 0.9c, then that thrust is pushing against 2+ times the mass, wouldn't that result in a slower increase in velocity?
Originally posted by sonhouseI think what you are missing, is that this is relativity we are talking about. So the question is: velocity with respect to whom?
But the effect of that acceleration is to not increase velocity at the same rate, right? If I am producing, say 1000 tons of thrust at zero velocity and 1000 tons of thrust at 0.9c, then that thrust is pushing against 2+ times the mass, wouldn't that result in a slower increase in velocity?
Originally posted by sonhouseOk, you are sitting in your spacecraft having accelerated to 0.9c.
Can anyone here answer a question in relativistic acceleration? My question is this: You have a space craft, from zero relative velocity, it starts accelerating at 1 standard g, 9.8 meters per second per second, and so forth.
If relativity was not a factor, it would reach the speed of light in about one year of such acceleration.
My question is, if at ...[text shortened]... ad a scale, would you still weigh 100 Kg like you did at the start or would it be different now?
Originally posted by googlefudgeThanks for that analysis. I knew the contraction formula, have it programmed into my old TI 84, but with what you said, I understand the implications a bit better, thanks everyone!
Ok, you are sitting in your spacecraft having accelerated to 0.9c.
The Lorentz factor [given by 1/((1/((1-((0.9C^2)/(C^2)))^(1/2)) ] is ~ 2.294
[or the inverse ~0.4359]
So you go to measure your weight. Your relativistic mass is 2.294 times your initial
mass, so your mass is now 229.4 kg.
BUT.
Weight is a measure of force, not mass. Your s ...[text shortened]... r. So you thus never measure your speed [relative to objects around you]
to be greater than C.
Originally posted by sonhouseNo, as you fly away from the Earth you observe events happening on the
I was thinking about the clock situation and it occurred to me that a time hack signal sent from Earth to your ship, say you were on your way to Alpha Centauri, a really great first interstellar stop since you get three stars for the price of one, but besides that, if you lasered or RF'd a time hack signal from Earth, even though you would have to frequency ...[text shortened]... you were hooked on since Earth clock would be going a couple times faster than ship clock time!
Originally posted by googlefudgeYes, but one of my jobs in the ancient past was in 1970 at Goddard Space Flight Center, working on Apollo Tracking and Timing. The tracking part was a transponder onboard the Apollo, and a radio link between Earth and Apollo as it was going to the moon.
No, as you fly away from the Earth you observe events happening on the
Earth as being slower than for you.
And that's even without relativistic effects.
Lets say you are travelling at 10% C, below the threshold of significant relativistic
effects, away from the Earth.
We start with you 1 light day away from the Earth at t=0 [18:00 UTC] which ...[text shortened]... ay you get, it takes longer and longer for each
program to reach you the farther away you get.
Originally posted by sonhouse
Yes, but one of my jobs in the ancient past was in 1970 at Goddard Space Flight Center, working on Apollo Tracking and Timing. The tracking part was a transponder onboard the Apollo, and a radio link between Earth and Apollo as it was going to the moon.
The transmitter on Earth sends a signal with a time hack code that when it reaches Apollo, the transp ...[text shortened]... d time shifts, maybe that would mess up the perceived frequency shift. Have to think about that.
That alone can tell you how fast you are going I think.In the theory of special relativity you are always stationary the rest of the universe is what is moving as far as you are concerned.
you get definite information about how close you are to c by the frequency you have to shift to to listen to the time hacksIf you measure the speed of light it always comes out at 299,792,458 m/s no matter what your speed is relative to any other given observer. It doesn't matter if you are accelerating or not. You can measure the rate your starting point, let's say the sun, is receding from you but you are always stationary. The sun is moving relative to the black hole at the centre of the galaxy, I copied and pasted this from Wikipedia to illustrate the point.
The Sun follows the solar circle (eccentricity e < 0.1 ) at a speed of about 255 km/s in a clockwise direction when viewed from the galactic north pole at a radius of ~8.34 kpc about the center of the galaxy near Sagitarius A*.We don't get two different figures for the speed of light if we measure it in the direction of the sun's movement or against it. So as far as we can tell the sun is stationary.
Originally posted by DeepThoughtYes, you should be able to look at spectrographic lines of the sun to check out Doppler shift but if you had a strong enough transmitter or laser it could be done also. There are schemes afoot that would use the sun as a giant lens to focus energy to drive a ship where all you need on board is fuel, you don't need to spend energy to speed up the fuel or you could use the collected energy to power a particle accelerator to get the exhaust close to c also which I think should increase your thrust since each particle would be 2.3 times its rest mass so getting the particles to 0.9 c should not be a problem as long as you have gigawatts of energy from whatever source you can use.That alone can tell you how fast you are going I think.In the theory of special relativity [b]you are always stationary the rest of the universe is what is moving as far as you are concerned.you get definite information about how close you are to c by the frequency you have to shift to to listen to the time hacksIf you m ...[text shortened]... is that by the time you are a light year away the signal isn't going to be very easily detected.[/b]
Originally posted by sonhouseI think you would be better off simply focusing the laser beams conventionally
Yes, you should be able to look at spectrographic lines of the sun to check out Doppler shift but if you had a strong enough transmitter or laser it could be done also. There are schemes afoot that would use the sun as a giant lens to focus energy to drive a ship where all you need on board is fuel, you don't need to spend energy to speed up the fuel or you ...[text shortened]... uri which is where I would put my money for a first interstellar voyage.
A three for one deal!