I wish to understand the theoretical concept of time travel whilst going FTL

Exactly. Even if relativistic time travel into the past were possible, there'd still be no way to do logic breaking shit like killing your grandfather.

I'm not interested in subjective time though.
I want to know whether warp ship arrives the same day as 0.2c colony ship that launched 500 years ago, or 100 years afterwards.
I want to know whether going back almost instantaneously will result in arriving 2 seconds after I left or 200 years later.
Is it true that a flight attendant at landing pad on that planet 100 light years away would first see a ship pop into existence then see its afterimage hurl backwards at 300,000km/s?

You asked for a picture. This is called a Minkowski Diagram.
We can’t draw in 4 dimensions, so all 3 dimensions of ordinary space are reduced to the X-axis of the left diagram. Motion to the left or right corresponds to movement in space. You’re sitting somewhere right now. You’re not moving. So there’s no motion left or right. But you ARE moving into the future at the rate of 1 second per second. The T axis represents motion in time. With every passing second, you move towards the top of the diagram. Any point in space or time can be shown on this diagram. Motion through space and time is, therefore, a line showing how you got there. This is called your “world line”.

Light travels 300,000 km/sec. A light ray is shown in red and marked C. The diagram has been scaled such that 300,000 km is 10 cm along the X axis and 1 second is 10 cm along the T axis. So the C line is halfway between X and T at 45 degrees. With me so far?

A ship leaves Earth and heads out into space. It travels along the cyan line T’. It is moving slower than light, so at all times light ray which left Earth when it did is further from Earth than the ship is. Slower than light motion is called Time-like.

The pilot of the ship regards himself as “not moving” once the engines are turned off. He’s just sitting there and it’s the Earth that’s rushing away. That’s a perfectly valid viewpoint and it’s why his path is labeled T’. He’s going straight up HIS time axis.

But ALL observers measure the speed of light to be the same. Light always moves halfway between the T and X axes. If the pilot has a different T axis than you do, he must also have a different X axis. Only way he can measure light to have the same velocity as always. His space-axis is X’ (continued)

Attached: Ansible 1.jpg (561x607, 28K)

Now, we’ll imagine an ansible has been invented. An ansible is faster-than-light radio. In fact, it’s instantaneous regardless of the distance between transmitter and receiver. Instantaneous is not really necessary. Any faster than light signaling will do, but it makes the diagrams easier to draw.

At 1, you broadcast an important message over the ansible. What does “instantaneous” mean? It means it takes no time to travel any distance in space. So the dashed gray line is horizontal. No motion in time at all. It is received by the space ship at 2.

The pilot sends a reply. How does it travel? Back to 1? No! That’s silly. Why should it retrace the path along your X axis. There’s nothing special about Earth’s motion. To be consistent, it has to go parallel to the ship’s X axis, the one we called X’. So it reaches Earth at 3. This is BEFORE you sent the original message at 1.

If the message sent at 1 was “planes hijacked to crash in New York”, then the police can take action at 3 to foil the plot. So the planes were never hijacked and you never sent the message at 1. We have a paradox!

Yes, if FTL was possible, the ship would arrive before its image, just as a supersonic jet leaves it sound in its wake.

Attached: Ansible 2.jpg (547x581, 29K)

>I wish to understand the theoretical concept of time travel whilst going FTL.
before you try to understand, try to understand the concept of simply going "as fast as light"
if you do understand it, you'll understand you could never go that fast, that therefore going FTL is not something that is realizably understandable

Attached: bounce762.png (600x241, 21K)

I imagine she would see some kind of "light boom" if she's standing close enough to the path of the ship, since the ship's movement would disrupt the light it's emitting in the direction of travel.
An observer on a planet midway between Earth and the destination system and a ways off to the side would first see the ship appear suddenly at the point where it was closest to him, and then see two images of the ship traveling in opposite directions away from the first point at the speed of light.

>I'm not interested in subjective time though.
There's no "objective time".

If you're just interested in the round trip, then read this wiki page: en.wikipedia.org/wiki/Twin_paradox

So it IS time travel.

Exactly.
Being able to travel faster-than-light (by ANY means, including hyperspace, warp drive, etc.) is equivalent to being able to go backwards is time.
Since the latter is considered impossible (paradoxes, causality violations), so is the former.

We can travel very close to lightspeed (and tour the galaxy thanks to time dilation) if we could solve some "minor" engineering problems -- such as the insane amount of energy required to move macroscopic objects at such speeds.

>There's no "objective time".
I'm struggling to formulate the question in manner that will actually get a satisfactory answer.
this guy meticulously explained how faster than light communication would clearly arrive into the past
while
This guy affirmed me in the assumption that instantaneous travel would indeed be instantaneous, and I could do a round trip to a planet 100 light years away in seconds for both me and whoever stayed behind on earth to measure it.

So, what now?

That's a good explanation of FTL communication between inertial reference frames, but what about OPs example in ? Let's assume that the destination planet is not moving relative to Earth, and also that the warp drive is instantaneous like the ansible. So when OP arrives at his destination, his Minkowski diagram looks the same as Earth's, only translated 100 light years along the x axis.
Now if OP uses the ansible to communicate with Earth, there's no way to violate causality, and he'll just be talking with the people that were there when he left.
Is that correct or am I missing something?
And what happens if the warp drive isn't instantaneous, but has a speed of 100 light years per second - does that change anything in the above example?

Because added a caveat.
"Even if relativistic time travel into the past were possible..."
In fiction, time travelers attempting to kill Hitler or their own grandfathers are always foiled by circumstances. The gun jams or something improbable intervenes.
Authors can be very ingenious. Either something prevents history from changing or the universe branches and a new time-track is formed. Shooting your grandfather doesn't erase you because you were born on the "old" track -- which you have no way to returning to now.

Since there's no evidence of either forces which keep the universe consistent or of alternate tracks, physicists usually prefer the simpler explanation that backwards travel (and FTL) just can't be done.

>Because added a caveat.
but he did reaffirm me when I said we are just talking reference frames, that is shit light and radio have to catch up with, not actually time traveling
added a whole new dimension into this
It's kind of confusing really
I grasped the backwards going afterimage fairly easily, but I'm having a hard time with, preventing 9/11 just because my information beats the speed of light

If everybody at both ends is in the same inertial frame, no problem.
But nothing enforces that restriction. Planets change velocity continually over the course of a year. It's not necessary to assume near-lightspeed ships. High speeds and instantaneous radios only make the situation more obvious. The longer the distance between the ends of the link, the slower you can go and still have causality violations.

Someone posted an informative link on another thread a few days ago
>galileo.phys.virginia.edu/classes/252/rel_el_mag.html
demonstrating the Relativity works even when the velocities are only millimeters/second.

Even if you posit that the ansible only operates when both ends are relatively motionless, all you need is TWO sets of transmitter/receiver pairs to cause trouble.
A (on Earth) transmits to B (motionless, 100 LY away). B uses ordinary radio to pass the word to C (near B, but moving) and C ansibles D (near Earth, but stationary with respect to C.)

Sorry, but that appears to be the way the universe operates. It takes a little while to absorb all the ramifications.

FTL either allows you to prevent 911 or you have to invent some reason why the past cannot be altered.

Believe me, physicists have devoted a great deal of efforts thinking of ways to avoid paradoxes. Kip Thorne (now a Nobel winner) "invented" a method of FTL travel for a friend (Carl Sagan) who was writing an SF novel. Of course, that meant time travel was also possible and Thorne and his students tried to think of a way out. Their best effort required an quantum mechanical effect which destroys any time machine the instant it's turned on (see Thorne's book "Black Holes and Time Warps" for details). Stephen Hawking proposed a "Chronology Protection Clause", some as-yet-undiscovered natural law which forbid backwards travel.

>Sorry, but that appears to be the way the universe operates
On paper, right?
I mean, this is purely theoretical technology that's way more impossible than possible, isn't it?
I would LOVE instantaneous FTL. Just one that pops you out 100 light years away 1 second later, not 100 years ago.
I really ruins the fun.

Yeah.
I'd also like zooming around the galaxy, exploring new worlds, finding new life and new civilizations (provided I wasn't wearing a red shirt).
But I only indulge in that during my "off hours", when I don't have to deal with Reality.

Despite the naysayers (and outright shitposters on Veeky Forums) all the experimental evidence points to Relativity being correct. Any new theory which supersedes Relativity (as Einstein replaced Newton) will have to predict the same phenomena in areas which have already been tested (as Einstein reduces to Newton at low velocities.)
We know that Relativity and QM aren't the Final Theories. They predict their own demises under extreme circumstances. It's very hard to find something better though because there's not much "wiggle room" left. :(

Do you allow yourself, to entertain the possibility, of there being means to create negative energy, or manipulate spacetime itself?

In my fantasies, yes.
>amazon.com/Making-Starships-Stargates-Interstellar-Transport/dp/1461456223
argues it's possible. He makes as good a case as any I've seen. At least it's not just handwaving.
I remain skeptical (about negative energy, anyway making FTL possible) for reasons I've already stated.

A physicist (Milton Rothman) impressed me once with a comment that we never really "create" anything. Electromagnetism, gravity, and the nuclear forces are "already there". The magnetic dipoles, for example, are "already there" in raw iron but largely cancel each other out. All we can do it arrange matter in such-and-such configurations that the forces do what we'd like done. That applies to everything from a simple magnet to a fission reactor.
So I don't hold truck with schlocky stories where the engineer-hero says "by cross-modulating the neutrino flow and polarizing the main deflector dish, we can create a beam of Omicron Particles which will...(dissolves into technobabble at that point, if not earlier.)"