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That FTL means time travel meme by Pierre-Simon Laplace - Sat, 16 Dec 2017 22:22:45 EST ID:hGyQlc1t No.57130 Ignore Report Quick Reply
File: 1513480965587.gif -(117244B / 114.50KB, 323x402) Thumbnail displayed, click image for full size. 117244
I have a question regarding this:
If you look at this gif it shows you "backwards" travel:
The first "jump" after the first acceleration points into the direction that corresponds to the lower left quadrant of the previous reference frame leading to backwards time travel.
However: Drawing it into the upper right quadrant should be equally legal which would imply forward time travel. This would imply that direction you are moving in space would dictate the direction of the "time travel" which seems entirely non-sensical to me.
I guess this is also the point but I still get the feeling I'm missing something here.
>>
Starfox !!S9+xB2BS - Sat, 17 Mar 2018 10:48:06 EST ID:NY7j51D6 No.57242 Ignore Report Quick Reply
>>57130
You (and pretty much everbody else) are forgetting that relativity treats space and time as one, and how it does so... the gif is also completely wrong in how to describe it.

For starters: You are always moving through spacetime at the speed of light,as expressed by a simple formula:

v(time) + v(space) = c

As "c", the speed of light, is known to be a constant, as v(space) increases, you have to reduce v(time) and vice versa.
v(time) is the "velocity" you move through time with.
v(space) is what you would regularily know as velocity. This variable cannot be negative, as simply reversing your ship still implies a positive velocity, just in another direction.

if v(space) > c, time would only go backwards locally on your ship (since c is constant, and v(time) would nescessarily need to be negative), not to external observers, as their v(time) and v(space) remains normal.

However with this normal, "unprotected" FTL travel in our spacetime frame, would also dangerously violate local and universal causality:

Imagine you are the pilot, and you lauched the ship when you were 20 years old (for simplicity, on your 20th birthday)... you engage your "normal spacetime frame" FTL drive after travelling a few years (say on your 25th birthday.). This will quickly hit a wall, as the time frame inside the ship quickly moves to the point where you pressed the button for your FTL drive and the ship hit light speed... with the end effect being that when you press the FTL button, nothing will happen, short of you accelerating to c and never passing the barrier.

IF it WAS to work, you would end up at a point where the local timeframe of your ship would be at the point where you launched the ship... There would NOT be 2 of you, as time for everybody else passes normally, and outside it's still the day of your 25th birthday. But local (ship) causality dictates that you and the ship should be on the launchpad... That travel would end up with you ripping causality apart when you leave FTL, as you have created your own time frame and causality that is completely disjointed from the rest of the universe and any consequences thereof.... or with pre-fetal you and a bunch of rocks travelling at FTL speeds, yet with everything else progressing as normal... until those bits hit the local causal and temporal point of the Big Bang :-O

In order to travel at FTL speeds in the first place, you will have to do one of the following:
>change "c" by moving into another domain where "c" is different
this is the core concept of most fictional hyperspace mechanics, especially Babylon 5 hyperspace or Star Control hyperspace/metaspace
>change v(time) by moving into another domain where v(time) is also rendered negative or 0 for the rest of the universe
you WILL need to have a positive v(time) inside the ship or you will violate local causality or never be able to leave (because if v(time) = 0 you will be frozen in time and never be able to leave the domain
>disjoint space and time
which cannot happen in our spacetime frame,as you cannot exist without space to inhabit your body, or time to enable your travel
>teleport (essentially ignoring the space part)
theoretically teleporting can solve the problem, however it's very hard and energy expensive to do so... plus, you would logically die while your "copy" reached its target due to the rules of quantum teleportation.
>exploit space itself
by moving space around your ship instead of moving the ship itself... the core concept of the Alcubierre/warp drive, so far the only viable method of FTL travel. It does not violate any of the above. Space in itself is nothing and contains nothing.. it does not have a definable "age" and it does not perform any actions on itself or surrounding matter, in essence. even if space is a part of spacetime it is not affected by time, just as time does not affect space itself (only its contents).
As space itself is also not an "object", by creating a pocket of spacetime to store the ship in (and moving the pocket itself), you can exploit a very important property of space, that it can EXPAND and CONTRACT at FTL speeds (as it provably did during the Big Bang).

Another way of exploiting space would be to punch a hole through its very fabric (a wormhole) and create a shortcut through spacetime... however whether this is possible is still unknown, as we don't have any idea yet of what or where this shortcut should pass through.

this should put a suffieciently large nail in that coffin... either nothing happens or you (very unlikely) destroy the Universe by creating a new Big Bang, take your pick...
>>
Karl von Weizsacker - Sat, 17 Mar 2018 11:58:33 EST ID:xNrGsoxl No.57243 Ignore Report Quick Reply
>>57242

im not disputing you here, simply seeking more information. where did the formula v(time) + v(space) = c come from? this is the first ive ever seen or heard of it
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Starfox !!S9+xB2BS - Sat, 17 Mar 2018 14:29:00 EST ID:NY7j51D6 No.57244 Ignore Report Quick Reply
>>57243
the formula is a very boiled down version derived from Lorentz transformation without fancy greek letters, which explains many of the concepts and limitations of Lorenzian/Einsteinian relativity and of the speed of light, electromagnetism and causality (all of which are the same).

there has also been written a huuuuge number of papers in the last 100 years trying to explain why backwards time travel is impossible,at least in this manner...

A good starting point is Lorentz' papers on the subject and Appendix I of the original paper on special relativity from 1916: http://www.archive.org/stream/cu31924011804774#page/n159/mode/2up
it contains Einstein's derivation of Lorentz transformation.
>>
Karl von Weizsacker - Sat, 17 Mar 2018 16:47:17 EST ID:xNrGsoxl No.57245 Ignore Report Quick Reply
>>57244

would you mind hopping on /chem/ and replying to my thread about atoms

>>>/chem/79012
>>
George Gamow - Fri, 23 Mar 2018 02:51:59 EST ID:HiPCHEgP No.57271 Ignore Report Quick Reply
>>57244
I'm a bit confused as it simply characterizes the dialation of time relative to the observer. I'm a bit lost how we make the leap to backwards time travel. We know despite relative motions of any direction, c is constant. Does this imply a specific orientation of spacetime? A perceivable "against the grain"? So backwards time travel can be more comparable to a sort if "temporal redshift"?
>>
Friedrich von Struve - Tue, 03 Apr 2018 00:01:33 EST ID:o31eHyLZ No.57274 Ignore Report Quick Reply
>>57242
>>
James Elliott - Wed, 16 May 2018 13:48:13 EST ID:+G8ef2Iy No.57279 Ignore Report Quick Reply
>>57271
you're pretty much correct in your basic understanding of how the speed of light works, but where things are confusing you is that what you've stated only applies to things that aren't capable of reaching and traveling the speed of light. once you move faster than light, causality is necessarily reversed by our understanding of the laws of relativity.

you see, the speed of light has fundamentally less to do with light than it does causality. the speed of light is more accurately the speed of causality, and photons just happen to have their velocity restricted by that boundary. so while light travels that speed, it's light itself is secondary to the more essential nature underlying reality that is causality.

knowing this, to travel faster than light means to travel faster than causality. to move faster than that any slower than light observer that could measure the properties of your spaceship or whatever would witness your actions occurring in reverse and vice versa.

interestingly enough, all that matters when it comes to the speed of light/causality is reaching it and breaking through it... that is to say, to do so isn't possible. if something were to simply exist moving faster than the speed of light or FTL travel becomes available somehow, moving faster than it doesn't negate the particles moving faster than it from experiencing relativistic effects of their own with regards to the speed of light, they just simply travel through time in reverse with respect to everybody/everything traveling below the speed of light.
>>
James Elliott - Wed, 16 May 2018 14:00:10 EST ID:+G8ef2Iy No.57280 Ignore Report Quick Reply
1526493610393.jpg -(69378B / 67.75KB, 877x500) Thumbnail displayed, click image for full size.
>>57279
this graph of a function where you try dividing by zero is a good, visually intuitive way of understanding the concept. the asymptote represents the speed of light and causality, and the curves on either side represent the velocity of any given particles traveling along on either side of that barrier. they are never capable of reaching the asymptote and, as my pic states, the curves will continue without bounds out towards infinity.

velocities traveled faster than the speed of light presumably behave symmetrically in terms of relativistic effects with velocities traveled slower than the speed of ligh, only with the direction/flow of time being reversed.
>>
James Elliott - Wed, 16 May 2018 14:01:43 EST ID:+G8ef2Iy No.57281 Ignore Report Quick Reply
>>57280
behave symmetrically in terms of relativistic effects with respect to velocities traveled slower than the speed of light***
>>
Arno Penzias - Mon, 21 May 2018 13:08:09 EST ID:457vC2+I No.57282 Ignore Report Quick Reply
>>57280
WADR, the mathematical consequences of attempting to reach the speed of light is because we define the speed of light as the maximum speed. The function of the relation between the speed of a photon and a tachyonic neutrino wouldn't be asymptotic but would simply be a ratio.

So I think it's misleading to say that the speed of light is the "speed" of causality. Tachyons would still obey causality in respect to other tachyons, just in a flow that is apparently opposite to events as ordered from our perspective. A hyper tachyon that traveled twice the rate of a normal tachyon would travel further into the past than it from our perspective, but from the perspective of the tachyon it is merely going further faster in the same direction as the slow tachyon, so they would experience retrocausality rather than acausality. So it makes more sense to me to think of the speed of light as a 180-degree 'fold' in causality, rather than a limit beyond which causality doesn't extend.


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