SoL from inside the spacecraft, what happens?

I guess my real question goes back to when I first heard about the concept of inertial frames of reference;

I feel like I’m not in motion, but that’s because I’m stuck at the bottom of a gravity well. In fact I’m moving at about a thousand miles an hour in a circular course about the Earth’s center of rotation. The Earth is moving at IIRC 30,000 miles an hour in an elliptical course around the Sun. The Sun rotates along with the rest of the galaxy.
In short, I’m presently a space traveler. I’m moving.
Just as time slows with increased velocity, it speeds up as velocity decreases.
If I hopped in my handy-dandy spaceship and adjusted my angular momentum to zero and cancelled out all relative motion could I ever become truly stationary?
Perhaps in relation to the Universal average angular momentum or something like that?
How fast would time go relative to you poor saps still stuck on the moving Earth?
Could I witness the rest of the history of the Cosmos go by like a really fast-motion film?
Inquiring minds need to know.

[If I hopped in my handy-dandy spaceship and adjusted my angular momentum to zero and cancelled out all relative motion could I ever become truly stationary? ]

all you would have to do is get out of the gravity well or counteract it somehow and don’t accelerate in any direction and you are at 0 velocity, no matter how fast you are moving.

Back to my OP, time dialation is the only thing that can slow you down (did some reaseach last night while sleeping). by time changing for the spacecraft passanger, it appears that he is traveling faster because he is getting somewhere in one year instaed of the 20 years as seen by his twin. the ‘twin’ will see the craft’s mass increase as it approached the SoL and it will never get there. BUT the spacecraft itself will continue to travel faster and faster - but time will change.
Now I am not sure about this part, but it might explains why the mass increases or at least changes. as the outside observer sees it you are gaining mass, as the ship see it, everything is normal except their clocks are running slower then the observer, but time seems to continue normal for them as well. the mass of the ship to the outside observer is compressed through time and increases, basically the ship os in 2 or 3 or 1.4 or whatever places at the same time and the mass increases beacuse of that?

The above premise meens that a passenger on that ship will travel up to and past the SoL at he preceives it. and will get to his destination at that speed (mainly because of the time dialation effect). But people back on earth and mars will have to wait a very long time for him to return due to him moving .999c acording to their clocks.

The only thing I see as a problem is that the destination would appear to be moving twards them at the SoL which is a no-no. but the destination can’t simply gain mass since it’s not accelerating.

The Earth is revolving around the Sun at about 67,000 mph.
(whee! feel that wind in your hair!)

There ain’t no universal reference frame to adjust to. But you could throw yourself into a black hole & watch the universe behind you appear to accelerate (time wise) into the future. It would be a bit of a one-way trip though.

From the OP:

Your acceleration is constant in the reference frame of the ship. An observer on Earth watching you will see time slow down for you as you approach the speed of light. Since time is slowing down, even though you measure constant acceleration, the acceleration you have with respect to the observer on Earth will decrease towards zero as you approach the speed of light. Thus, you never get to the speed of light.

Okay, there’s where the problem is. There is no velocity. There is only velocity with respect to a given reference point. The same thing goes for time and distance. For a given observer (i.e. the reference point) time will slow down for you.

There is no “stationary” any more than there is an “up”.

Phobos;

No, but I feel the solar wind in my magnetotail!
Oops! There went another plasmoid!

Make that, “For a given observer (i.e. the reference point) time will slow down for you as your relative velocity increases.

Einstein never postulated what would happen at speeds FTL because an object with positive rest mass cannot possibly accelerate past C. Theories have been offered as to what would happen if an object with negative mass accelerated past C, and one of them includes backwards time travel, but I don’t know if it’s ever been proven. Makes great scifi, though.

It is true, however, that at relativistic speeds, time dilation does occur. If you are traveling at 90%C, time would be going slower for you than for someone at rest relative to you. If you compared clocks when you got back, you would notice a difference. The faster you go (relative to someone else) the slower time goes (relative to someone else.) This has been proven with atomic clocks, and is an important visual aide in understanding why C is always a constant. Time dilation occurs precisely because the speed of light is always the same!

What happens is all the photons collect on the wall at the far end of the spaceship. Later, when you stop accelerating, they all fall at once with a humorous “Thump!” noise.

I’m not sure if i missed it somewhere in the thread or not, but I don’t think that some of the posters are appreciating the differentiation between acceleration and motion. Correct me if I’m wrong but the only waarping of the passing of time occurs during the acceleration process, once one has accelerated to .99c and sets the cruise control on said vessel, then time will relativistically be the the same as it is on a relatively slow vessel (say the earth).
of course now that I have typed this all out, it sounds kinda fishy to me, but rather than deleting it, i think I’ll throw it out there and maybe get schooled, cuz I actually have managed to confuse my self about the relationship between relative motion and an acceleration in relativity…
spank me…

It’s an important distinction. An object travelling at a contant velocity (no acceleraton) is exactly the same as an object not moving at all. Why? Well, suppose you’re in space travelling at 30mph. Another spaceship beside you is travelling 30mph. Since there is nothing else to act as a reference point, you might as well be standing perfectly still. Indeed, there is no such thing as “perfectly still” since there is no universal reference point. Everything standing still is simply moving with the exact same velocity vector as the thing you are comparing it to.

Acceleration, on the other hand, means your velocity is increading (or decreasing) with respect to the velocity of another object.

Acceleraion is the same thing as gravitation. If you accerate at 9.8m/s^2 in outer space, you have “artificial” gravity. This is where gravity and time get all mixed up together and your brain explodes.

E d’Mann:

I’m not a real PHd. I hope to be some day, but it won’t be in physics it will be in chemistry. I find relativity very interesting, and I am familiar with some of the common issues people have with it but I’m no expert. My post handle is a second hand reference to a cult-popular cable television puppet show.

kgriffey79:

I find that one should always be careful about calling others stupid before making a supposedly grand pronouncement on a particular topic. It can be very difficult to retract if you are wrong. First of all, Einstein never said this. If you can provide citations showing otherwise, I’ll gladly look a them. The equations for time dialation describe an asymptotically slowing of time of the traveler from the rest obsever’s reference frame. It makes no sense to describe a situation at or beyond the S.o.L. using these equations. Such descriptions lie beyond the scope of relativity.

k2dave:

You forget that it is all relative. From the spaceship’s reference frame his destination is traveling toward him at 0.999c. It will appear to the traveler that his desitination is experiencing time dialtion, Lorentz contraction, and increases in mass. These observations are due to the relative velocities of the reference frames. If the space craft decelerates to his destinations reference frame all the relativistic effects he observed will disappear.

Let’s assume two observers.

Observer A is on the spaceship

Observer B is ouside watching the spaceship

Let’s also assume the spaceship has an infinite amount of massless fuel (just go with me on this).

Also, through the magic of hypotheticals assume Observer B can clearly see the spaceship and Observer A throughout this whole process without violating any physics or ‘moving’ himself.
Ok…

Observer A, throughout his entire trip (even if it is forever), will never notice anthing change. His watch ticks like it always has, he’s still 6 feet tall, the ship is accelerating at a constant 0.0064 mi/sec/sec and he measures the speed of light at 186,000 miles per second. He will observe all of this to be true from day 1 of the trip till the end of his life 70 years from now. To help you buy this imagine Observer A has no windows in his spaceship. Indeed, if we want to say he was born there then as far as he knows the inside of the ship is the entire universe. As far as he is concerned he is standing still in a gravity well (acceleration and the effects of gravity are indistinguishable from each other…this is called the Equivalence Principle).

Now, Observer B knows different. He put the baby on the ship and has watched it race away. Observer A gets closer and closer to light speed but never quite reaches it. Observer B also notices that while the spaceship is spewing out the same amount of fuel it always has it is accelerating slower and slower. Instead of 0.0064 mi/sec/sec we’ll say it’s now down to 0.000064 mi/sec/sec. Again through the magic of examples Observer A measures the spaceship and Observer A’s mass as increasing. No wonder it’s slowing down.

Question: Why does Observer A notice no difference? Why doesn’t he notice a slowing of acceleration?

Because time is slower AND distance is smaller…his rulers are shortening compared to Observer B’s rulers.

So, he is now only accelerating at 0.000064 mi/sec/sec but since his ruler has shortened one mile to Observer A seems like 1/1000[sup]th[/sup] (or whatever it really is…I’m not up to the math) of a mile to Observer B. Since time also slows down when Observer A starts his stopwatch it will run slower than Observer B’s stopwatch. When measuring the speed of light Observer A’s photon has less distance to travel from Observer B’s perspective and Observer A’s watch will slow (compared to Observer B) in a combined manner to give him exactly the same measurment for the speed of light as Observer B.

Finally, another way to look at what would happen to you if you reached the speed of light –

An infinite mass may be hard to swallow so take it from another angle. Distance shortens for you as you approach light speed. This will have the effect of making the universe appear smaller (to you). At light speed the universe will be the size of a point to you. You are now effectively (from your perspective) everywhere in the universe at once. Neat huh! Unfortunately, from your perspective, if you decided to hit light speed for just the briefest moment, say as fast as you could hit the button to start and then stop (i.e. hitting a button twice), the universe would come to an end before you could turn your engines off. Not so neat…

thats the missing piece of the puzzle
[Lorentz contraction]

as the traveler approaches c, the perceived distance would increase. you could accelerate more but doing so would only ‘push’ your destination further away. So much for my 3 year trip to Alpha Centuri.
so due to Lonentz contraction is it worth accelerating any more or just cruse at 0.99c.

Here’s more of my oversimplification that I don’t know if it is true or not, but it seem to fit:
I have read that for photons, anything is infinite distance from them and they are not moving through time, the Lorentz contraction and time dialtion fits here. for a photon everything is ‘pushed’ further away - very very far away, but since time doesn’t exist, it can travel through space.

Actually, the opposite happens. To an observer watching the ship, it takes the ship four years to get there going 0.99c. In the traveler’s eyes, the distance to Alpha Centauri contracts as they accelerate, and the trip takes about 15 weeks.

I have no idea what you are talking about. As far as photons and time, by our equations, anything moving at the speed of light does not experience time as we know it; no time elapses for them from the beginning of their journey to its end.

[Actually, the opposite happens. To an observer watching the ship, it takes the ship four years to get there going 0.99c. In the traveler’s eyes, the distance to Alpha Centauri contracts as they accelerate, and the trip takes about 15 weeks.
]

so how fast can one get from point A to point B using distance from an observer not on a ship and using time as observed on the ship?
According to the above post it is possible to effectivally travel FTL IF you are willing to also travel into the future.

We are always traveling into the future. Moving between two positions cannot be done without moving through time as well. Space and time are inextricably linked. Asking to measure the distance in one frame of reference and the time in a different one makes as much sense as measuring the x & y distance between point A and B in one frame of reference, and the z distance between them in a different one.

You are never going FTL. By accelerating, you alter your frame of reference to one where the distance is shorter, and then by decelerating, you return to your previous frame of reference. The journey still took 4 years, even though you experienced less time.

If I have a very good (but not theoretically impossible) drive that lets me travel arbitrarily close to the speed of light, then I can get anywhere I want in an arbitrary short amount of time. If I go .99999999 times the speed of light, I can cross the observable Universe in my lifetime (ok, I fudged the math… Fridays are my day off. The point is, it’s possible to cross he Universe.) From anyone else’s viewpoint, time has almost stopped for me, so it just takes me a heckuva long time to die of old age. From my viewpoint, the Universe has flattened out to the extent that my destination is now just a hop, skip, and jump away. Regardless of whose viewpoint, I still reach there before dying.

It’s not clear if it’s possible to actually “move” faster than the speed of light (it’d take imaginary mass, not just negative… Even weirder), but there may (or may not) be a few ways to get the same effect, using wormholes or warp bubbles or whatever. To produce one of these, you do need negative mass. The thing is, that any method which can give you effective FTL travel (meaning you arrive there before light could), can also be used to give you time travel into the past, even if you do use one of those funky backdoor methods like wormholes.

[You are never going FTL. By accelerating, you alter your frame of reference to one where the distance is shorter, and then by decelerating, you return to your previous frame of reference. ]

ok let me rephrase, it is possible to travel 4.5 light years (here to alpha centuri) in lets say 3 year as measured by time on the ship? I’m not concerned about how old or dead people are on earth.

No, you won’t travel 4.5 light years in 3 years. I tried to express why in my previous post:

Maybe this will help show why. Start out with two points, a & b:


    a

    b

Next, map two frames of reference on top of them, Q & R, each of which have their x & y directions swapped with the other.


       Q                R
 ^                 ^
 |  a              |  a
 |                 |
x|                y|
 |                 |
 |  b              |  b
 +- - - ->         +- - - ->
     y                 x

Now, the distance of two points from each other, in two dimensions, x & y, is sqrt(x[sup]2[/sup] + y[sup]2[/sup]). Let’s take the x distance from frame R, and the y distance from frame Q.

Well, the x distance in R happens to be zero, as does the y distance in Q, and sqrt(0[sup]2[/sup] + 0[sup]2[/sup]) = 0, so the total distance is zero. Therefore, a & b are the same point!

Except they’re not. You can’t use measurements from different frames of reference without transforming them into a single frame of reference. Otherwise, the calculations you get are gibberish.