Time Travel Violates Thermodynamics. Here's why

How can time travel violate thermodynamics? I'm glad you asked!

Time is not a physical force. We see time when we perceive change. Our body ages after time, the sun rises and sets after time, seasons change after time, that we all perceive. But when we really understand this change, we see more than time.

Our body cells die after thousands of division cycles, this planet rotates to change what side faces our sun, the Earth revolves around our sun and its tilt changes how much light we receive. Explain natural phenomenons, and we know they are not caused by time but by natural processes.

Some say time makes up a fourth dimension, but every thing caused by time is really a change in three dimensions. You will be more accurate to say time is the derivative of space rather than an addition to it.

Time is change in space, and the 2nd law of thermodynamics states every change increases overall entropy of our universe. We define more entropy as a state with more possible ways of creating it. In order to go back in time, we would need to recreate a condition of less entropy. We cannot create a state with less possible ways of existing, which is what scientists mean by saying we cannot decrease entropy. So, we cannot recreate past conditions with less ways of existing, and that means we cannot time travel.

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Does that all make sense? My premise of time as change might not feel intuitive, but when you see it that way the whole idea of "time travel" clearly can't happen.

But we all know the opposite of Entropy is growth and change, and the great Changer of the Ways, Tzeentch, has the power to change the threads of fate as It wills. To deny the possibility of Change is to deny Tzeentch!

Question though: Time travel going backwards changes entropy levels. What about going forward in time?

Silentpony:
But we all know the opposite of Entropy is growth and change, and the great Changer of the Ways, Tzeentch, has the power to change the threads of fate as It wills. To deny the possibility of Change is to deny Tzeentch!

lol

Question though: Time travel going backwards changes entropy levels. What about going forward in time?

Forward time travel means creating the state that will result after enough natural processes happen. In theory you could predict that, but before you measure and calculate every cell and particle the future state will already arrive!

Make a macrosystem into a state millions of years in its future, though, and you could have time to accelerate physical processes and quicken the future state. In effect you cause your system to time travel forward by making a state of higher entropy come quicker, like by burning a lot of matter. I imagine space engineers of the future will find a use for making a future state real today, and practice forward time travel for a galaxy.

No force of time, though, and no chance of going into the past. The process would be much more gradual and boring than the movies.

Manage to perfect near light speed travel, and you will change less than things around you and be years, centuries, or milleniums into the future by the time you stop. Light speed is the best option for forward time travel according to relativity.

secretkeeper12:

Some say time makes up a fourth dimension, but every thing caused by time is really a change in three dimensions.

No, time actually is a fourth dimension. We exist in four-dimensional spacetime. The postulates of relativity (which are based on empirical fact, most famously by the Michelson-Morley experiment) cannot be satisfied without adding a fourth dimension. These are:

1.) The speed of light is observed to be the same by all observers in all inertial reference frames
2.) The laws of physics are the same in all inertial reference frames

An alternative formulation of the second postulate is "There is no privileged reference frame." What this means is that the uniform motion (motion with constant velocity) of one's own reference frame can be detected only by observing another reference frame, and that when this relative motion is observed it is not physically meaningful to ask which frame is moving and which is stationary.

An inertial reference frame is a member of the class of coordinate systems none of which is accelerated with respect to any other coordinate system in that class. That is to say that in an inertial reference frame, Newton's laws are valid, and in observer in one reference frame will always observe Newton's laws to be valid in any other reference frame.

There are many approaches to the mathematical derivations, which vary in their formality and accessibility, but the most famous and easiest to understand is Einstein's own thought experiment involving a laser reflected by a mirror in a moving train car.

Fix a reference frame to the side of the train tracks, call it S. Fix another reference frame to a point inside the train car, call it S' (read as "S-prime"). A device on the center of the floor of the train car emits a pulse of light. In S', the light rays reach the front and back of the train at the same time. The two events, a light ray reaching the front and a light ray reaching the back, are said to be simultaneous. The events are separated only in space.

However, to an observer on the side of the tracks in S, something different happens. The rays of light must have the same speed in both S and S'. But in S, after the light flashes but before the rays of light are emitted, the front and back of the train car have moved. The observer in S sees that the back of the car catches up the rays and the front is moving away from them, so the two events in this frame are no longer simultaneous. The events are now separated in space and in time.

This leads us to a bit of a paradox. What, exactly, happened? Did the rays of light hit both walls at the same time, or did the rays hit the back first, and then the front? If we consider time to be separate from space, then only one of these can be true. This violates the second postulate, as it would imply that a physical process happened differently in two different frames, and therefore different physical laws were in effect.

To resolve this paradox, we abandon the idea that physics happens in three dimensional Euclidean space with time as just a parameter. When we say that an n-dimensional space is Euclidean, what we mean is that the distance between two points is given by the Euclidean metric, the length of the hypotenuse of the right triangle connecting the origin to the point. If the point is given by the ordered n-tuple (x1, x2, x3, ..., xn) then the distance from the origin is (x12 + x22 + ... + xn2)1/2. Instead of Euclidean space, we now say that physics happens in four-dimensional Minkowski space.

Minkowski space is very different from Euclidean space. In Euclidean space, the elements of the space are points and they are connected by straight line segments. In Minkowski space, the elements of the space are called events and they are connected by what is called the spacetime interval. If two events are separated by dt units of time and dr units of distance, then we say that the spacetime interval is given by ds = (c2dt2 - dr2)1/2 where c is the speed of light. The reason we do this is that the spacetime interval between two events is invariant, meaning that it has the same value in every reference frame. If we two events are separated by dr and dt in S and by dr' and dt' in S', then even if dr is not equal to dr' and dt is not equal to dt', we still must have ds' = ds. By describing physical processes in terms of spacetime interval we are now able to satisfy the second postulate.

tl;dr It is not possible to disentangle time and space, anything that happens in space also happens in time.

You will be more accurate to say time is the derivative of space rather than an addition to it.

Nope. A derivative is an operation on a function that is defined on a smooth manifold, it is not a property of the manifold itself. Space itself is not a function of anything, you cannot take its derivative with respect to anything.

And in any case, to say that time is the derivative of space would mean that time is tangent to space at each point in space, which wouldn't be physically meaningful.

Time is change in space, and the 2nd law of thermodynamics states every change increases overall entropy of our universe. We define more entropy as a state with more possible ways of creating it. In order to go back in time, we would need to recreate a condition of less entropy. We cannot create a state with less possible ways of existing, which is what scientists mean by saying we cannot decrease entropy. So, we cannot recreate past conditions with less ways of existing, and that means we cannot time travel.

No. The reason that we can't go backwards in time has nothing to do with entropy or thermodynamics.

Let's go back to our discussion of Minkowski spaces and intervals. Given any two events separated by ds in a reference frame S, it is always possible to find a reference frame S' in which those two events are simultaneous, that is, separated only in space. To be in this reference frame, the observer must not have any speed relative to this frame, the observer is then said to be at rest in this frame and for this reason we call this the rest frame.

One of the consequences of relativity of simultaneity is that while the time that separates two events A and B depends on the reference frame, their order does not. If A happens before B in any one reference frame, then A happens before B in every frame, except for the rest frame in which A and B are simultaneous. The only way to observe the order of events as being reversed is to be travelling faster than the speed of light relative to the rest frame of the two events. This is of course not possible.

Let's say I wanted to go back in time to see the signing of the Declaration of Independence. This happened in 1776. So let's say I were to somehow build a time machine. What would happen is I would turn the device on in 2018, step through, and then arrive in 1776. This is a violation of relativity of simultaneity. 1776 happened before 2018, so this must be true in every reference frame. But in the reference frame attached to me, my departure (which happened in 2018) would have to happen before the signing of the Declaration of Independence (in 1776).

Entropy doesn't have anything to do with it. All that it means for the entropy of a system to increase is that it's entered into a state in which work needs to be done on the system in order to return it to its previous state.

Does that all make sense?

Er, no. Sorry to say. You've got a lot of studying ahead of you want to really be able to understand this.

Hooray, we have a physicist!

renegade7:

This leads us to a bit of a paradox. What, exactly, happened? Did the rays of light hit both walls at the same time, or did the rays hit the back first, and then the front? If we consider time to be separate from space, then only one of these can be true. This violates the second postulate, as it would imply that a physical process happened differently in two different frames, and therefore different physical laws were in effect.

Light seems to move to an observor on the train to a different spot because they experience the same change in space as the light. An observor on train tracks experiences less change in space, so they perceive change in the train as well as change in light.

The key here is perceiving. Each observor differs in perceiving because each experiences a different motion, or change in position. Less change for the one on the track makes them perceive change in train as well as change in light.

It's really psychology, when you think about it. One perceives more change than another.

Nope. A derivative is an operation on a function that is defined on a smooth manifold, it is not a property of the manifold itself. Space itself is not a function of anything, you cannot take its derivative with respect to anything.

And in any case, to say that time is the derivative of space would mean that time is tangent to space at each point in space, which wouldn't be physically meaningful.

I always see a derivative as change in state because of change in variable. Any change due to any variable seems to fit, and all variables come together as time for a state that depends on many variables.

.
Let's go back to our discussion of Minkowski spaces and intervals. Given any two events separated by ds in a reference frame S, it is always possible to find a reference frame S' in which those two events are simultaneous, that is, separated only in space. To be in this reference frame, the observer must not have any speed relative to this frame, the observer is then said to be at rest in this frame and for this reason we call this the rest frame.

In other words, no change in space compare to the system.

One of the consequences of relativity of simultaneity is that while the time that separates two events A and B depends on the reference frame, their order does not. If A happens before B in any one reference frame, then A happens before B in every frame, except for the rest frame in which A and B are simultaneous. The only way to observe the order of events as being reversed is to be travelling faster than the speed of light relative to the rest frame of the two events. This is of course not possible.

Let's say I wanted to go back in time to see the signing of the Declaration of Independence. This happened in 1776. So let's say I were to somehow build a time machine. What would happen is I would turn the device on in 2018, step through, and then arrive in 1776. This is a violation of relativity of simultaneity. 1776 happened before 2018, so this must be true in every reference frame. But in the reference frame attached to me, my departure (which happened in 2018) would have to happen before the signing of the Declaration of Independence (in 1776).

Your reference frame exists because past acts created it. Those past acts created a frame with more possible ways of existing-more entropy-so it will always exist instead of past frames.

Entropy doesn't have anything to do with it. All that it means for the entropy of a system to increase is that it's entered into a state in which work needs to be done on the system in order to return it to its previous state.

Why do the laws of physics work like they do? Not because an equation says they do, but because it's how nature and the universe work.

Entropy always increases because more entropy is more likely. Time includes every change that increases entropy. I see all laws of physics as connected, and change to increase entropy is what's constant.

Er, no. Sorry to say. You've got a lot of studying ahead of you want to really be able to understand this.

Don't we all? I'm an eager student engineer, though I try to stick with real concepts more than abstract math.

I see math as a way of thinking and perceiving rather than reality laws. If we didn't have a sense system, we couldn't see any math and it just would not exist. Unlike the universe, math needs an observor to exist.

(I also think math expresses human intellect to a great extent. Math grammar is a nightmare, though! I don't see why professors bombard students with abstract concepts and abstract conjugations, but that's a thought for another thread.)

Time travel violates every law that is named and unnamed, not just thermodynamics.

Ok, let's start with a quote:

"The second law of thermodynamics states that the total entropy can never decrease over time for an isolated system, that is, a system in which neither energy nor matter can enter nor leave. "

I would like that you pay especial attention to the part where it says "over time". Because you are going to wrong way. You are stating that change and entropy come before time. But the basic statement from the law. You can't base an argument in a law while not afhering to the lettering of said law.

When you are attempting to define time as change you are being too vague. What is change? A solitary ball in the middle of space does not change, but one may define time for it without change. In change you need a before and an after, because that metric, the measurement in time is what links the change to an object. Vhange is dependant on time, not the other way round. One may define time for a Universe that has experienced Heat Death, but not change.

Also as manner do not quote a result lf a theory while trying to dismiss the theory itself. Time dilatation is a result of seeing time as a dimension, and if you dismiss that idea the Laplace transforms that govern said dilatation do not have any place.

Also also, the inertial frame references have nothing to do with psycology. The thought experiment is just a way to make it easier to think about it. The spped of light is the same for all frames of reference. That is what the Michaelson-Morley experiment quoted before showed. Because those weren't people seeing light, it was an interferometer, light interfering with itself.

Edit: Could go into more detail but it is 2:30 AM and need to get some sleep.

Regardless of the science behind time travel possibilities, human nature has more or less already shown time travel isn't possible. Seconds after the inventor of time travel shows his discovery to the first person he decides to show it to... the chance someone will use it to go back and invent it first starts to increase exponentially. The end point of that being that human kind will never discover time travel; because logically if we ever do, we already would have.

Kyrian007:
Regardless of the science behind time travel possibilities, human nature has more or less already shown time travel isn't possible. Seconds after the inventor of time travel shows his discovery to the first person he decides to show it to... the chance someone will use it to go back and invent it first starts to increase exponentially. The end point of that being that human kind will never discover time travel; because logically if we ever do, we already would have.

I'm not going to dismiss it on the basis of a Fermi's Paradox (Asking where the time travelers are and concluding they don't exist because we can't see them.), and the less said about the paradox involved in trying to be the inventor first because you learned how from the real inventor, the better.

Between you, me, and the very obvious bot on the wall, I'd say that the action of time travel is probably possible because ANY movement in time (The long way around.) is possible. The issue is that a proper understanding of it is not known, merely theorized and, from there, assumptions made. I won't dismiss it because of a lack of understanding of the thing, either. Too many things that ARE true suffer under that failing, so until a real practical attempt is made and can be studied, let's just ennjoy the ride, as it is.

renegade7:
Let's say I wanted to go back in time to see the signing of the Declaration of Independence. This happened in 1776. So let's say I were to somehow build a time machine. What would happen is I would turn the device on in 2018, step through, and then arrive in 1776. This is a violation of relativity of simultaneity. 1776 happened before 2018, so this must be true in every reference frame. But in the reference frame attached to me, my departure (which happened in 2018) would have to happen before the signing of the Declaration of Independence (in 1776).

Ok so I think I understood nearly all of that (damn you Engineering requirements...), but it does leave me with one question regarding this part in particular (though I guess it might be able to apply to here->future as well).

You already mentioned above that relative simultaneity holds true for every frame except the rest frame. If a time travel machine could access this rest frame, couldn't a person then step from their origin space/time event into any other space/time event due to them all happening at once? This would necessitate the changing of their reference frame from their old one to a new one though (ie: current frame -> rest frame -> new frame).

Kyrian007:
Regardless of the science behind time travel possibilities, human nature has more or less already shown time travel isn't possible. Seconds after the inventor of time travel shows his discovery to the first person he decides to show it to... the chance someone will use it to go back and invent it first starts to increase exponentially. The end point of that being that human kind will never discover time travel; because logically if we ever do, we already would have.

Unless there is a cataclysmic event that stops such travel going further back in time than it. Say the machine can do time but not anywhere other than the relatively equivalent location, and the invention occurs on a different planet after the Earth is abandoned/destroyed as an example.

Kyrian007:
Regardless of the science behind time travel possibilities, human nature has more or less already shown time travel isn't possible. Seconds after the inventor of time travel shows his discovery to the first person he decides to show it to... the chance someone will use it to go back and invent it first starts to increase exponentially. The end point of that being that human kind will never discover time travel; because logically if we ever do, we already would have.

That is, unless the act of time travel creates a divergent timeline that we dont experience

Space doesn't exist without time. The Four dimensions require all of the other dimensions to be there as well or none of them would exist.

Time travel is at its most horrific when you realise going back 30 years in time alone will put you at some spot in the middle of outer space 30 years ahead of where the Earth will eventually be. Not even a spiffy Delorean can help you there!

Squilookle:
Space doesn't exist without time. The Four dimensions require all of the other dimensions to be there as well or none of them would exist.

Time travel is at its most horrific when you realise going back 30 years in time alone will put you at some spot in the middle of outer space 30 years ahead of where the Earth will eventually be. Not even a spiffy Delorean can help you there!

Ah, but where was the Earth 30 years ago? There's no stable point of reference to determine these things.

But yeah, an important point, one that's usually totally overlooked.

This reads eerily close to what somebody who decided to sacrifice a science module or two to go and get their Chong-on instead would say. Not saying it is, only that it bears some resemblance.

Thaluikhain:

Squilookle:
Space doesn't exist without time. The Four dimensions require all of the other dimensions to be there as well or none of them would exist.

Time travel is at its most horrific when you realise going back 30 years in time alone will put you at some spot in the middle of outer space 30 years ahead of where the Earth will eventually be. Not even a spiffy Delorean can help you there!

Ah, but where was the Earth 30 years ago? There's no stable point of reference to determine these things.

But yeah, an important point, one that's usually totally overlooked.

One can actually mathematically plot it with a relative amount of accuracy. The calculation only really becomes unwieldy once you start getting into thousand+ years time. If you wanted to "jump" further than that backwards/forwards, have the machine pop out every 500 years or so, reorient, and "jump" again.

Avnger:
One can actually mathematically plot it with a relative amount of accuracy.

Sure, but you are plotting it compared to an arbitrary point, or rather landmarks ("spacemarks"?). Which are also moving around. Your location is only relative to other known locations.

Avnger:

Kyrian007:
Regardless of the science behind time travel possibilities, human nature has more or less already shown time travel isn't possible. Seconds after the inventor of time travel shows his discovery to the first person he decides to show it to... the chance someone will use it to go back and invent it first starts to increase exponentially. The end point of that being that human kind will never discover time travel; because logically if we ever do, we already would have.

Unless there is a cataclysmic event that stops such travel going further back in time than it. Say the machine can do time but not anywhere other than the relatively equivalent location, and the invention occurs on a different planet after the Earth is abandoned/destroyed as an example.

But then you have to start explaining why there are such limitations. The problem there is if we are assuming that time travel IS possible, then assuming that there would be any limitations at all makes about as little sense. If someone could time travel at ALL what is to stop them from overcoming whatever "limitation" that one could pose on time travel. It's like one of the stranger UFO arguments. If a species possessed the technology to travel through interstellar space... why wouldn't they have already developed the safety measures necessary to prevent themselves from hitting a telephone pole and crashing in New Mexico? Its just odd to assume one massive leap in technology wouldn't have already overcome lesser challenges in achieving that technology. Especially when you are talking about time travel where you would have to assume that even if there were limitations on the technology when it is first created, not overcoming limitations assumes that no one could or would eventually overcome that limitation.

undeadsuitor:

That is, unless the act of time travel creates a divergent timeline that we dont experience

Then, what's really the point of going forward with "time travel" at all. Sure, the person travelling experiences the divergent timelines... but that's from that traveler's point of view. From the point of view of anyone else, the "time machine" is basically a Futurama suicide booth. The traveler goes into it, and is never present on this particular timeline ever again. Might as well make a suicide booth and just say its that kind of time machine, it would have exactly the same effect on this timeline.

What if you made some sort of entropy cannon that you can use to fire the excess entropy back into the original time so it doesn't go into the past?

Kyrian007:

undeadsuitor:

That is, unless the act of time travel creates a divergent timeline that we dont experience

Then, what's really the point of going forward with "time travel" at all. Sure, the person travelling experiences the divergent timelines... but that's from that traveler's point of view. From the point of view of anyone else, the "time machine" is basically a Futurama suicide booth. The traveler goes into it, and is never present on this particular timeline ever again. Might as well make a suicide booth and just say its that kind of time machine, it would have exactly the same effect on this timeline.

I never said it was a good thing, I was just reply to the idea that time travel could exist without current evidence of it.

I mean hell, the divergent timeline theory is how 99% of time travel shows and movies work already. Think of stuff like Back to the Future. Only people in the delorian experience time travel. Everyone else exists as if they lived through the changes because they did.

I mean think about it, unless a time traveler is stupid enough to leave behind d incredibly obvious evidence, how would we know they changed the past? Maybe the past used to be different and it's already changed and were living in another timeline already.

undeadsuitor:

Kyrian007:

undeadsuitor:

That is, unless the act of time travel creates a divergent timeline that we dont experience

Then, what's really the point of going forward with "time travel" at all. Sure, the person travelling experiences the divergent timelines... but that's from that traveler's point of view. From the point of view of anyone else, the "time machine" is basically a Futurama suicide booth. The traveler goes into it, and is never present on this particular timeline ever again. Might as well make a suicide booth and just say its that kind of time machine, it would have exactly the same effect on this timeline.

I never said it was a good thing, I was just reply to the idea that time travel could exist without current evidence of it.

I mean hell, the divergent timeline theory is how 99% of time travel shows and movies work already. Think of stuff like Back to the Future. Only people in the delorian experience time travel. Everyone else exists as if they lived through the changes because they did.

I mean think about it, unless a time traveler is stupid enough to leave behind incredibly obvious evidence, how would we know they changed the past? Maybe the past used to be different and it's already changed and were living in another timeline already.

Mostly I'm sure we don't live in a universe where time travel is possible because even though the answer would keep changing, we'd all know the answer to one question... "who invented the time machine." Even if someone went back, invented the time machine just to keep it quiet and try and "fix" history... there would still eventually be someone who would eventually abuse it for profit and in some way leave evidence of time travel. And even if someone is successful, the timeline would correct... and that guy that invented it in the original timeline or someone close to his level (say the guy that would have invented it next, or the next guy, or the next guy... on to infinity) would "re-discover" it and invent it again, starting the cycle over. Plus the past is an escape. There are dozens of ways an extinction level event can wipe out humanity... before eventually our sun grows cold and goes out. Time travel isn't possible, because those humans have not already retreated into the past to escape that eventuality. Or it is possible, but human kind won't eventually advance far enough to achieve it before being wiped out.

Actually I'm generally more positive about time travel in terms of the original idea of project Quantum Leap (holograms in a simulated environment) or Steven Baxter's The Light of Other Days (rewinding omnipresent objective recall.) Basically a system where the past can be viewed but not interacted with in any way. They seem more possible to me because there isn't any problems with causality, no chance of paradox. And just like time travel, they are both horrifying in their own ways.

I think time travel is impossible because it violates the law of conservation of matter and energy. If you displace an object in time, that means that it's physical existence must be overlapping with another moment in which it also exists (since even if a thing is destroyed it's component atoms still exist, or the energy that those atoms represent). This would both remove matter/energy from the present, and add matter/energy to the past or future, whichever direction the object travels, resulting in a change in the total energy of the universe, which is impossible; thus, time travel is impossible.

The second law of thermodynamics refutes the possibility of creating some devices (perpetual motion machine) and many physics phenomena (more answers can be found on the site). And I agree with the author. The phenomenon of entropy proves the impossibility of traveling through time. But at the same time, we know about the existence of black holes, but don't understand how the processes take place there. We have only guesses. And how the time-space flows there remains inexplicable and the statement about the time travel remains unproven.

renegade7:

There are many approaches to the mathematical derivations, which vary in their formality and accessibility, but the most famous and easiest to understand is Einstein's own thought experiment involving a laser reflected by a mirror in a moving train car.

Most of what you wrote went way over my head but I do know about Einstein's theory of special relativity that says time speeds up or slows down depending how fast you move relative to something else. Say, someone inside a spaceship that moves at the speed of light would age much slower than someone on earth. Inside the four-dimensional fabric of space time gravity also bends time as objects inside the fabric move on a curved path and that curvature of space is gravity. Due to time dilation astronauts for example return to earth 38 microseconds younger with every day they spent in outer space.

Going by special relativity the only way for time travel would be to create a wormhole between two points in space-time. But ofcourse, there is no technology to create a wormhole and apparently these collapse very quickly and are only suitable for small particles. Another way would be for a spaceship to move at the speed of light around a black hole and for 5 years in the spaceship 10 years on earth will have passed. I read that even without a worm or black hole it could be possible to time travel at warp speed by bending space time inside a doughnut shaped vacuum by letting focused gravitational fields form a closed time-like curve.

Seems difficult to accomplish but, maybe a few hundred years from now? :p Black holes in particular would be revolutionary if science could ever figure them out.

 

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