FTL without paradoxes?

[BAYLOR]

Which is what I was getting at in post #42. You make the jump, but it doesn't violate causality because you're no longer in the same universe. In that circumstance time travel and FTL are actually jumps to different universes at times or locations different than the start point in the previous one.

Which offers some obnoxious possibilities for fiction writers.

The first reference in fiction I ever to to the notion of alternate timelines was in the book Lest Darkness Fall by L Sprague de Camp. It was written in 1939.

 

[Onyx]

The first reference in fiction I ever to to the notion of alternate timelines was in the book Lest Darkness Fall by L Sprague de Camp. It was written in 1939.

That beat the scientific Many Worlds theory out by 18 years.

 

[BAYLOR]

That beat the scientific Many Worlds theory out by 18 years.

The character Martin Padway who was sent back to 6th century Rome. wondered whether changing the past would cause him to cease to exist. Then he hit upon the notion that he was creating alternate branching of history .

 

[goldhawk]

Which is what I was getting at in post #42. You make the jump, but it doesn't violate causality because you're no longer in the same universe. In that circumstance time travel and FTL are actually jumps to different universes at times or locations different than the start point in the previous one.

Which offers some obnoxious possibilities for fiction writers.

Why is there an universe that is almost identical to our own lying waiting for you to jump to?

And because of Relativity, every timeline has a corresponding space, making that space the preferred frame of reference in that universe.

 

[Dave]

Thanks to @goldhawk I understand now why special relativity makes FTL totally impossible, even if it were through some wormhole or other construct still based within four dimensions. However, it is obvious from this thread that people have very great difficulty dealing with different frames of reference within only four dimensions. I do also understand that completely because it is alien to our everyday experiences. So, is it not possible that within string theories that require many extra dimensions of space time for their mathematical consistency (Bosonic string theory - spacetime is 26-dimensional, Superstring theory - 10-dimensional, M-theory - 11-dimensional) that there could still be some possible way to jump between our four dimensions that we cannot possibly comprehend? For the sake of a good story, can't we just say, yes?

 

[Onyx]

Why is there an universe that is almost identical to our own lying waiting for you to jump to?

And because of Relativity, every timeline has a corresponding space, making that space the preferred frame of reference in that universe.

It isn't waiting, it is created by the fact of taking an existing universe and dumping a spaceship into the middle of it, just as a time traveler appears out of nothing in some prehistoric cave.

Neither is a very normal or likely event, but there aren't as many specific barriers to an object suddenly appearing in a quantum universe than there are barriers to violating causality. I'm not selling this as likely, just less impossible.

 

[Onyx]

For the sake of a good story, can't we just say, yes?

We can always say "yes". The point of the debate in this thread is whether you can write a convincing reason that causality wasn't violated that a high school physics student can't dissect.

Sometimes handwaving is much more convincing than a detailed refutation of science that readers find erroneous. Science fiction writers get themselves in trouble when try to be more clever than physicists. It is a similar problem to the crime novel where a revolver has a safety, a medical mystery where someone gets a transfusion without blood typing or a thriller where the pilot flies a plane through fog by the seat of their pants.

Ringworld is a cool idea, and fortunately Niven didn't tell us that the ring is made of nanotubes. Instead he chose a fictional super-material that an engineer wouldn't immediately see was too weak. That's the line I'm talking about.

 

[goldhawk]

It isn't waiting, it is created by the fact of taking an existing universe and dumping a spaceship into the middle of it, just as a time traveler appears out of nothing in some prehistoric cave.

Now that is hand waving. To create an universe takes a tremendous amount of energy.

Neither is a very normal or likely event, but there aren't as many specific barriers to an object suddenly appearing in a quantum universe than there are barriers to violating causality. I'm not selling this as likely, just less impossible.

But there is one very big barrier: the Second Law of Thermodynamics.

 

[Onyx]

Now that is hand waving. To create an universe takes a tremendous amount of energy.



But there is one very big barrier: the Second Law of Thermodynamics.

The Many Worlds theory says that the multiverse is bifurcating constantly already. I have never heard of an equation for the energy costs of creating a universe, which is little more than a mathematical construct. Energy within a universe is a separate concept.


Thermodynamics would apply, but that doesn't mean that the ship or whatever would be appearing without some balancing trade in some opposite direction. Maybe the wormhole blows one ship's mass worth of X-rays out the other end, like how black holes return energy to the universe.

 

[goldhawk]

The Many Worlds theory says that the multiverse is bifurcating constantly already. I have never heard of an equation for the energy costs of creating a universe, which is little more than a mathematical construct. Energy within a universe is a separate concept.

You said the universe was created. Therefore it requires energy to create all the mass and energy within it.

Thermodynamics would apply, but that doesn't mean that the ship or whatever would be appearing without some balancing trade in some opposite direction. Maybe the wormhole blows one ship's mass worth of X-rays out the other end, like how black holes return energy to the universe.

I wasn't talking about the First Law. The Second Law says that the probability of a spaceship just appearing from nothing is so small that it will never happen.

 

[Onyx]

You said the universe was created. Therefore it requires energy to create all the mass and energy within it.



I wasn't talking about the First Law. The Second Law says that the probability of a spaceship just appearing from nothing is so small that it will never happen.

Are you not familiar with the many worlds theory?

 

[zmunkz]

Heh, we are drifting a little afield of the OP. I’m keen to follow, though.

Many worlds is an interpretation of a model, more than a theory in and of itself. I think it has fallen out of favor. It doesn’t call for a creation, so-to-speak, more like a forking. Every quantum outcome actually plays out, infinitely splitting earlier moments so they can all be realized. The energy budget of any single universe is constant. It is an awful lot to take on board just because we have a model that appears to show a wave-function collapsing at measurement. The more I’ve researched this, the more I’ve settled into the instrumentalist camp, when it comes to physics equations.

The second law of thermodynamics doesn’t apply to the universe as a whole, since the universe is likely not a closed system. People worry about this one a bit too much I think.

I don’t find multi-world or even alternate timelines very likely. It’s a completely ungrounded concept. My own sense of time travel, if it were possible, is that it would have to exist within a single timeline. Quantum mechanics, as @Onyx noted, does allow for uncaused events (radioactive decay, virtual particle formation, tunneling, etc), and it does allow for matter to spontaneously jump into a state that happens to match a fully formed human with memories of their travels through time. The odds are zero, for all intents and purposes, but it is not disallowed.

Seems to me this cleanly solves the grandfather pradox. Once you go back in time, you seize to be a part of the causal chain that brought you to the moment of departure (which, by definition, must be forward-facing in time), and you appear, as far as that past is concerned, as a remarkable, but random, quantum event. Now if you kill your grandfather, future you is never born, but time traveler-you is not causally linked, and lives on. For all you know, traveler-you actually is just a quantum anomaly and your “memories” are just down to the state you brain popped into.

I’ve also wondered what role uncertainty might play. Perhaps the more tightly you control the time or position of your arrival, the less you can control the energy or velocity you have when arriving. I always thought this would make for an interesting short story.

 

[goldhawk]

Are you not familiar with the many worlds theory?

I am. But you said the universe was created by the time travel. In the multiverse speculation, multiple universes already exist.

And you can replace the multiverse speculation with superposition. Rather than having one universe fork into two, a superposition of the two universe is created which will eventually collapse back into one at some future time.

 

[Onyx]

I am. But you said the universe was created by the time travel. In the multiverse speculation, multiple universes already exist.

And you can replace the multiverse speculation with superposition. Rather than having one universe fork into two, a superposition of the two universe is created which will eventually collapse back into one at some future time.

That's a rather odd way of looking at the multiverse. The many worlds interpretation of quantum mechanics implies that the universe is constantly dividing whenever two paths are offered - they both come into existence at that point, and not before. That sort of multiverse doesn't already exist, its parts come into being over time in a process like cell mitosis.

That is what I'm referring to, and it certainly does imply that new universes are coming into being.

 

[goldhawk]

Nothing odd about it. If the universe becomes two, each would have have the energy. The First Law of Thermodynamics. If both have the same energy as their parent, where did the energy come from? Again, the First Law of Thermodynamics.

 

[Onyx]

Nothing odd about it. If the universe becomes two, each would have have the energy. The First Law of Thermodynamics. If both have the same energy as their parent, where did the energy come from? Again, the First Law of Thermodynamics.

The laws of thermodynamics are the underlying mathematical rules that a solitary universe exists under. Much like a video game only has so many gold coins programmed into it. If you make a copy of that video game, the new copy will also have a full complement of coins.

If you create a new universe, you don't have to imbue it with things like mass or energy - mass and energy are expressions of the universe's programming, not things external to universes that must be pumped in like petrol.

When it comes down to it, a "universe" is a bounded mathematical expression, and you can clone information as much as you want.

 

[Dave]

And how many angels can dance on the head of pin? Just sayin'

 

[goldhawk]

The laws of thermodynamics are the underlying mathematical rules that a solitary universe exists under. Much like a video game only has so many gold coins programmed into it. If you make a copy of that video game, the new copy will also have a full complement of coins.

If you create a new universe, you don't have to imbue it with things like mass or energy - mass and energy are expressions of the universe's programming, not things external to universes that must be pumped in like petrol.

When it comes down to it, a "universe" is a bounded mathematical expression, and you can clone information as much as you want.

That means there is something outside our universe. This contradicts the evidence that our universe is completely within itself.

 

[Onyx]

That means there is something outside our universe. This contradicts the evidence that our universe is completely within itself.

There is no possible way to have evidence that there is nothing outside of our universe. That just doesn't make any sense - a completely untestable theory.

 

[Onyx]

And how many angels can dance on the head of pin? Just sayin'

Is this an inappropriate discussion for people interested in writing science fiction to be having?