The quantum physics discussion in my Holiday Dinner Table thread got me thinking about time and space, what is bendable, what isn’t, whether General Relativity is a viable theory and so forth, and naturally I started considering the possibility of time travel. Here’s how I know it is impossible:
Time doesn’t exist. It is a manifestation of the human imagination. Things change; the world changes, we change and everything seems to be in flux somehow. Even if an object takes millenia to destruct and end, it inevitably does, similar to entropy, I suppose, in the sense that there is a systematic degradation involved in all things. Nevertheless, my point is that things are always changing, and of course distances between objects exist, but time itself does not exist. It is merely a subjective measurement system.
www.achrongame.com - Proves that time travel will exist in about ~200 years. Its just that only achronal beings remember what happened in the previous iterations.
I think general relativity does in fact prove that time does exist, as we can measure different rates of the passage of time using satellites and gps, etc.
If you want to travel in time, simply wait a few seconds
But that’s not really what we mean by time travel as a scifi concept, we mean somehow transcending the natural flow of time either fowards or backwards.
Time travel into the future is certainly possible, it’s the backwards travel that is impossible.
If you want to travel into the future, do a single close orbit near to a black-hole’s event horizon. You’ll come out of that orbit, depending on how close it is, far into the future, perhaps hundreds or thousands or millions of years, yet for you only a few hours or days will have seemed to pass.
Yes, in that sense, time travel is perfectly possible, but only into the future.
Well if cryo technology is ever perfected, that would be, essentially, time travel into the future (Futurama, anyone?). But yeah, just ask Walt Disney when he wakes up.
Thanks for the info, Anenome. But is there any way to actually get that close to a black hole? Also, how is it determined that you can, indeed, time travel when it’s never been done? And a black hole of all things? Why exactly?
This was my thought coming into this thread, and I’m glad you pointed it out.
Time, past, present, future are figures of speech; they’re concept**s. When we speak of “the past” or “the future”, we’re speaking figuratively about imaginary arrangements of matter. Matter exists in its current arrangement. That’s self-evident but sufficiently mindblowing to merit pondering. The capacity to think in terms of a concept so abstract as time, and to act upon predictions derived from those thoughts, and to communicate that data probably requires a brain so amazing I feel humbled to posses it.
Yes, actually. We could do it now actually. Basically you take a nuclear power source, combine it with an ion engine with a hydrogen scoop, and begin picking up momentum towards the black hole. The crazy thing is that, the faster you go the slower time moves for you, another property of special relativity (although how the universe knows you’re moving faster than other things I have no idea unless there’s an actual universal frame of reference, which to this point we don’t think there should be).
So, half way to the black hole you’re picking up speed, and you could get to a pretty significant fraction of light-speed, say .99999% or so. At that speed and higher, you’d have considerable time-dilation effects–time moving slower for you than outside your frame of reference, meaning the universe would seem to be moving at fast-forward.
Then, once halfway there, you flip the ship around and begin decelerating, until at your desired black-hole orbital speed. Aim for a precise orbit around it, at a precise speed, and skim the event horizon. Do that, and you could watch thousands of years pass before your eyes in a matter of seconds. You’d see the stars dance and skip, see galaxies crash together, and stars wink out one by one or explode as stellar fireworks. You might even witness the heat-death of the universe (perhaps, if you strayed inside the event horizon. And if your black hole didn’t explode.).
Anyway, even doing all that, it would still take something like 1,000 years to reach the nearest black hole, as perceived from inside your ship.
You could do it a lot faster if you could figure out a way to use a black hole on the other end to slow you down, so you didn’t have to start braking at halway. Hmm, maybe like the reverse of a gravitational slingshot. Don’t think I’ve ever heard anyone propose that maneuver before. It may not really be possible. No way to get directly oppositional gravity to your line of travel, only tangent to it, which would only accelerate you further.
Now, if we manage to someday figure out how to create artificial gravity, then we may be able to to create a ship that travels faster than the speed of light, or at least to greatly improve acceleration to that speed. I actually think we may indeed be able to do it eventually.
Read up on this link and you’ll get it. It’s called gravitational time dilation, and is a real thing that’s verified and all that.
There was a pretty cool episode of Star Trek Voyager where the ship entered a planet with a massive time dilation effect around it. While the ship simply tried to enter the atmosphere, the inhabitants below called it a star or a moon. For a thousand of their years, it hung there in the sky
When we talk of moving through a physical dimension, it’s in reference to time. At time t, we’re at x, at t+1 we’re at y, at t+2 we’re at z. What does it mean to move through time? At t we’re at t1, at t+1 we’re at t2, huh? What does it even mean? Subjectively, it might mean that your experience of time is that you were at t1, then at t2, but physically there’s no movement in time, just a frozen 4D universe.
OP is correct. All conceptions of time boil down to a comparison of two distances. The distance between two locations of a clock hand compared with the distance between two locations of a car on a racetrack; the distance between two locations of the constituents of a cesium atom in an atomic clock compared with the distance between two locations of a ball in the air; the distance between two locations of the Sun compared with the distance between two sets of positions of molecules in a wilting flower.
Comparison is an action, hence for the purposes of physics (rather than the loose sense of everyday talk), “time” is a verb. One can travel through an object or space, but one cannot travel through a comparison! Perhaps something else is meant by “travel through time,” but that awaits coherent definition.
I don’t know much about special relativity and a connection between space and a concept—time. But I don’t think anyone’s saying time is a meaningless concept. I support OP and AJ and Blargg, perhaps in my ignorance.
However the idea that you can manipulate a concept (e.g. time, a la Anenome) as though it weren’t just an abstract thought in your brain seems silly, and I’ll be the first to say that’s probably due in part to my ignorance on the subject. But I’m willing to guess that behind all the definitions what’s really being described is just laws of physics, not the ability to experience arrangements that don’t exist.
I would disagree with the characterization of what I said as “maniupulating time.” Experiencing a slower time reference via strong gravity or acceleration is just as possible as hearing different octaves of sounds via the doppler effect and speed differentials.
That’s my point. Time is not merely an abstract thought. An abstract thought is the number two. You may see a collection of indistinguishable objects and develop this idea of “two.” But that’s in no way connected to physical reality in a causal sense. Looking at special relativity, you can see and ultimately observe that time is a parameter of physical reality.
To the person within strong gravity, time outside his frame of reference would appear to travel faster depending on the strength of that gravity.
To the persons outside that gravity, the person in strong gravity would appear to have time moving slower, depending on the gravity strength difference.
So, when I wrote about seeing stars explode and galaxies collide, that’s not seeing into the future, but rather the idea that under strong enough gravity the person in that gravity could see in a few seconds light that was generated over the span of thousands or millions of years.
It’d probably be pretty bright There’s an energy shift when time goes through a gravity effect. Ordinary light could blue-shift to, say, become gamma radiation. So, you might not even see much if it all gets massively blueshifted
Everything is traveling through time. That should make it clear why time-travel in the fictional sense is impossible. Time is nothing else but the the causal relation.
Because time is the causal relation, it too is governed by the law of conservation (causality implies conservation). The conservation law is the essence of physics - if matter cannot be created or destroyed, then whenever the distribution of matter is altered from equilibrium, a surplus and deficiency are created simultaneously. For example, if you mount a fan in your window and push air out of your house, this increases the pressure outdoors and decreases the pressure indoors by precisely the same extent (per volume). If you move a billiard ball from one end of a billiard table to the other end of the billiard table, the density of billiard balls on the end from which it was removed must decrease and the density on the end to which it was moved must increase.
Perhaps not quite as obviously, this same principle operates in time. If you strike a billard ball and it moves across the table unimpeded, no motion is deducted from the ball, except by friction which we are neglecting. If you strike the exact same ball with exactly the same force, angle, etc. and place another billiard ball in its path, something different will happen to the struck ball - its motion (energy) will be reduced when it encounters the ball in its path. In order to impart motion (energy) to a body, motion (energy) must be given up to exactly the same extent by the causal body.
By definition, the effect cannot be the cause, so time travel is not even coherent, let alone possible.
Isn’t causality just the intuition our minds have for conceptualizing experience of time?
I mean, living for all our lives in “normal” flow of time ingrained the implications (“causality”) so deeply in our minds that we take causality for granted. Add to this cultural and genetic inheritance of our ancestors living for all their lives in “normal” flow of time.
What makes you believe causality is actually fundamental? I am not denying it is, BTW, I am just unsure.
