Author Topic: a thought on FTL  (Read 5907 times)

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Offline Bobboau

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I just considered something, as an object approaches the speed of light it's mass increases to infinite, strong moving masses cause frame dragging, objects in a dragged frame can appear to move faster than the speed of light (particles within the ergosphere of a black hole), wouldn't this mean that as a ships approached the speed of light it would drag spacetime with it and thus be able to appear to move faster than the speed of light?
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Offline Scotty

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Big problems are 1) getting that fast takes a huge amout of energy, because the object is gaining mass, which takes more energy, etc. and 2) all inertial reference frames must be equally valid or relativity gets thrown out the window, and we can't have that.

Also, I'm not certain that causing a dragged frame and being in a dragged frame are necessarily the same thing.

 

Offline Davros

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what type of mass does an object gain ?

 

Offline watsisname

I think this may be a confusion of rest mass vs. relativistic "apparent" mass.  The latter doesn't actually cause an increase in gravitational field from the frame of the object (I think?).  From an external frame, I wouldn't know.

edit -- I'm really drunk, not really trying to think this through right now.  inb4 herra
« Last Edit: September 11, 2011, 03:02:47 am by watsisname »
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Offline Kosh

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Nah, it will appear a certain way based on this.
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Offline Firstdragon34

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I wouldn't imagine a space ship would be gaining mass when activating the FTL. Why would it gain mass when space is moving around it?
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Offline Bobboau

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because that is how relativity works. time moves slower, distance gets shorter in the direction of motion and mass goes up.
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Offline watsisname

Relative to an observer in a different inertial frame of reference.

Relativistic mass follows the expression m=γmo, where gamma is 1 over the square root of (1-v2/c2).

The key term here is v, which is the relative velocity between the object and the observer.  An observer on a fast-moving spaceship sees no such increase in mass.

So I'm mostly sure that there isn't actually any increase in gravitational field strength for an object accelerated to high velocities.  Also my understanding is that it's not even the mass that should be discussed in this aspect of relativity, but rather the momentum.  Apparently a number of physicists seem to prefer to avoid the concept of relativistic mass altogether.  Unfortunately I'm not well versed enough on this subject to be comfortable going much further into it.
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Offline Bobboau

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yes, well the hypothetical space ship would be moving relative to the two end points of it's journey, and what we are interested in is what everything looks like from the three perspectives. if mass increases as velocity increases, then shouldn't the reference frame appear to drag space along with it more? and then shouldn't the apparent speed of light go up in that region? I don't know, it seems sort of like a contradiction. I posted it here because I know there are a few people who know their physics and would be able to tell me why not.
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Offline Firstdragon34

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In truth, I don't know my Relativistic Physics so my understand that space is a fabric and it can be warped. My in-depth understand of how the FTL works is very little. I understand subspace from Freespace that is about it. ;p
A small voice in my head tells me they are have followed us here in the Milky Way. They follow us until we are dead at their feet. We are nomands of the stars, no longer the race that was loved by the Great Elders. My name is Kyral and this is my story of survival.

There is no sanctuary for us, in this Universe. We will fight the Terror for one last time on this Shining World. May the Transcendent judge us kindly in the Life Stream.

 

Offline Mika

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and then shouldn't the apparent speed of light go up in that region?

This particular comment motivated me to write something on this thread. The interesting result of the nature related research is that no matter the state of movement of the observer or the source, when measuring the speed of light, one will always find it to be c. This is confirmed by multitude of experiments, and no-one has ever been able to detect any difference. Note that I have to add that this is according to current understanding, this addition is meant for those people who might happen to read this 500 years later in the future and laugh about the stupid beliefs of 2000s and so that I don't look completely silly. Seriously though, particles going faster than c have been sought in multitude of experiments, but no-one has ever been able to find one. If you can, Nobel prize is awaiting for you!

"Speed of light is a constant." What this means is surprisingly hard to understand, since it contradicts common sense.

To screw your minds more, when photon starts from the vicinity of a large mass and travels towards space, it undergoes a red-shift, i.e. it loses energy. When it goes towards a large mass, it experiences blue-shift, and thus gains energy. Even though speed of light remains at c, its energy content doesn't! Makes you kind of feel that at least something is conserved, doesn't it? The way I explain this to myself is that either time unit or distance metric (which are basically the same thing) screws us since they don't behave in a linear sense close to the relativistic speeds or large masses.
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Offline Bobboau

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ok, the thing that got me thinking about this was this, if the space is moving at the speed of light, such that if you moved against at the speed of light it you would appear to remain constant, then what would happen if you moved with it?
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Offline Firstdragon34

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Well, if you are constant with light then it would appear that you are not moving right? I think I'll go with Frank Herbert's Folding Space for now.
A small voice in my head tells me they are have followed us here in the Milky Way. They follow us until we are dead at their feet. We are nomands of the stars, no longer the race that was loved by the Great Elders. My name is Kyral and this is my story of survival.

There is no sanctuary for us, in this Universe. We will fight the Terror for one last time on this Shining World. May the Transcendent judge us kindly in the Life Stream.

 

Offline Nuke

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dune never really attempted to explain how their ftl worked as far as i can remember (maybe there was something in heretics/chapterhouse, but its been years since ive read those). it did require that the navigators had some degree of prescience for reliable navigation, hince why spice was so important for space travel. if you accept the brian herbert/kja books as cannon (i do not), space travel was not impossible before the holtzman engines were invented, but this form travel took months. they really did not explain it in depth but for that kinda travel in that amount of time i think you would still need a form of ftl. i think dune just assumes einsteins theories were wrong, or at least did not accurately model relativistic travel.
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Offline watsisname

@bobboau

Heh, well moving against the motion of the ergosphere completely (ie, maintaining a fixed radial position relative to the center of the black hole) is impossible, because that requires moving at the speed of light. ;)

In practice though I don't think the situation would be any fundamentally different than considering your maintaining a fixed position exactly on the event horizon -- in both cases you're precisely countering the "motion of space".  In both cases you appear infinitely red-shifted and time-dilated for an external observer, because the photons lose all energy trying to escape the horizon.

Edit:  Though I stress that for the example of the ergosphere, that's for the observer being behind your current direction of motion.  The ergosphere rotates around the hole, so photons leaving you on different vectors (eg, tangentially outward to your path of motion, or forward along with it) certainly do escape with energy to spare.  This means that parts of your path around the hole are visible, with varying degrees of red or blue-shift and time dilation.  You'd appear slowed down and red-shifted while moving away, sped up and blue-shifted while moving towards.
« Last Edit: September 14, 2011, 11:29:27 am by watsisname »
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Offline Dragon

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I think that folding space in "Dune" is just that, some device used to compress ("fold") space between two points and travel through it as sub-light speeds. Energy requirements are atrocious, but it doesn't contradict laws of physics (according to one theory, at least). While matter nor energy cannot exceed speed of light, space can (and does so when expanding).

 

Offline Bobboau

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sped up and blue-shifted while moving towards.

this is that part that interests me, how sped up?
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Offline jr2

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So, I have a question:

A laser fired in the direction of travel from a spacecraft travelling at 0.25c, would an outside observer be able to measure the light travelling at 1.25c or would it end up being 1.00c??

 

Offline Bobboau

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DEUTERONOMY 22:11
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Offline watsisname

Indeed, 1c, regardless of the velocity of the observer.  The speed of light in vacuum is constant and independent of the frame of reference of the observer or the motion of the source.

jr2:  Your example is based on a principle that sounds really weird and contrary to common sense, yet is demonstrably true.  Velocities are not linearly additive, which means you can't simply add the numbers together as you'd expect.  If I'm driving down the road at 60mph, and I throw a baseball out the window at 40mph (relative to me in the car), and I throw the ball in the same direction that I'm driving, then you'd expect to be able to say that the speed of the baseball relative to the ground is 60mph + 40mph = 100mph.  But this would be wrong!  It's actually 100mph minus a tiny little bit, that little bit is because of relativity.

If you examine the math behind this, the effect ends up being insignificant at small, every-day speeds that we're used to, but very significant at speeds close to that of light.


Bob:  I'm really not sure how to answer that exactly -- it would depend on your speed and trajectory around the black hole, the black hole's mass and angular momentum, as well as the position of the observer.  It's mathematically too involved for me to be willing to try to go through, sorry. :P

I suppose what I can do is recommend looking at this website that Astronomiya provided for me a while back during a similar discussion on black holes and relativistic effects.  It's a really nice one and might help provide further insight. :)
In my world of sleepers, everything will be erased.
I'll be your religion, your only endless ideal.
Slowly we crawl in the dark.
Swallowed by the seductive night.