Why I think perhaps time-travel is impossible

[Pulchra]

Think about it, if you for example use a strong magnet to speed things up in sort of an attempt to travel in time, people would notice and resist the changes, so only nature would change and speed up or go backwards, but I have the suspicion that the same would happen to nature also, that it would resist it, I wouldn`t go as far to say that energy is alive, but nature certainly is and sometimes when I pray for a god to exist, I think about something that I can`t really explain, a thing in nature, like an ore almost of something bright and living, so with this said, I suspect a little that time-travel itself is really close to impossible because there`s always something to resist it and it might prove that everything`s living, even materie

 

[Hammster]

If time travel were possible, we’d know about it.

 

[Under One King]

In theory, there is a way you could "time travel" to the future, but it would involve traveling somewhere at the speed of light or faster for hours, depending on how far into the future you wanted to go.
Traveling to the past is impossible.

 

[d taylor]

God's is the only time traveler.

 

[Elear]

We all travel through time constantly. We just don't control the rate or direction (if those terms even apply, depending on what time is).

 

[Sabertooth]

First rule of time travel, "Only leave when the Earth is moving away from you...!"

 

[Freth]

Think about it, if you for example use a strong magnet to speed things up in sort of an attempt to travel in time, people would notice and resist the changes, so only nature would change and speed up or go backwards, but I have the suspicion that the same would happen to nature also, that it would resist it, I wouldn`t go as far to say that energy is alive, but nature certainly is and sometimes when I pray for a god to exist, I think about something that I can`t really explain, a thing in nature, like an ore almost of something bright and living, so with this said, I suspect a little that time-travel itself is really close to impossible because there`s always something to resist it and it might prove that everything`s living, even materie

I don't believe God would allow time travel, for the same reason He doesn't allow us to find life on other worlds—sin. If man could time travel, it would be a mess. If man could have contact with other sinless created beings, it would be disastrous. I think God purposefully put limitations in place, in the laws of the universe and in shrouding other created beings from our view, so that we can't do what our sinful nature would surely cause us to do, completely ruin things.

 

[Palmfever]

I don't believe God would allow time travel, for the same reason He doesn't allow us to find life on other worlds—sin. If man could time travel, it would be a mess. If man could have contact with other sinless created beings, it would be disastrous. I think God purposefully put limitations in place, in the laws of the universe and in shrouding other created beings from our view, so that we can't do what our sinful nature would surely cause us to do, completely ruin things.

Agreed.
He appoints us individually a period of time to travel through. James, 4:14. Yet you do not know what your life will be like tomorrow. You are just a vapor that appears for a little while and then vanishes away.

1 Cor, 13:12. For now we see through a glass, darkly; but then face to face: now I know in part; but then shall I know even as also I am known.

13 And now abides faith, hope, charity, these three; but the greatest of these is charity.

 

[keith99]

If time travel were possible, we’d know about it.

As most present it, yes. But the form Heinlein used in The Door Into Summer it could be quite possible and not know to us. Simply put where it works but with 2 equal masses and it is unknown which goes backwards and whoch goes forwards. Also a square (or was it cube) law as to energy consumption so while workable for proof of concept useless in practice. Well except for one major blackout!

One other possibility is that black holes provide for time travel. BUT again not useful. The individual protons and electrons may make a jump, but nothing more organized than that.

 

[sjastro]

Here is some serious science on whether time travel can be accomplished by travelling faster than light.
It amounts to posing problems such as can an answer be given before a question is asked.

A simplified Minkowski diagram in a rest frame is composed of a vertical t axis (expressed in units ct so it is dimensionally the same as the x axis) and a horizontal x or space axis.

For a photon travelling at c the world line or path in space time forms a 45⁰ angle with the t and x axis as it undergoes equal displacement in both time and space.
Note the line forms a part of the light cone in the Minkowski diagram.

An event is defined as having a position and time coordinate.
If two events occur on the x-axis in the first diagram then each event is only separated in space, there is no temporal displacement as each event occurs at t=0.
This has important consequences as there is no ordering of the events.

This is not a problem for particles travelling at velocities less than c where the world line forms an angle less than 45⁰ with the time axis.
This is because length contraction and time dilation causes the time and space axes to undergo rotation which is the geometrical version of the Lorentz transformations.

For each observer the degree of rotation depends on the velocity of the observer but if each observer travels at less than c they will always be in the time like region (inside the light cone) where causality is not violated.

If the observers travel faster than light they fall in the space like region (outside the light cone) where causality is violated.
In this case it is possible to define events purely on the x-axis but as shown there is no temporal displacement or time ordering of events.

In the diagram in the time like shaded region event O definitely comes before event P, outside this region in the space like region one cannot tell if O comes before Q or Q comes before O.

From a physics rather than maths perspective what this is amounts to is that O and Q occur in such rapid “succession” that the time difference is less than the time needed for a light ray to traverse the spatial distance between the events.

So it is possible for an observer travelling faster than light to answer a question before it was even asked.
Definitely not because the speed of light cannot be exceeded.

 

[SelfSim]

Could go all hypothetical here and suggest Krasnikov tubes(?)
(Paper here: A Superluminal Subway: The Krasnikov Tube)

AIUI, Krasnikov tubes are (hypothetical) ‘spacetime tunnels’ which allow for superluminal travel without violating causality, but only for round trips and with much larger energy requirements than say, the (hypothetical) Alcubierre drive.

I'm still trying to figure out the spacetime diagram for one, so I can't explain it yet .. any takers?:

 

[Truthsearcher1]

It depends how you define "time travel". In the general sense, like others have said, everything in the universe is constantly travelling in time, because everything is in motion through space. Even just one second into the future is considered time travel.

Otherwise, the only thing about time travel that is impossible would be backwards time travel. Time can speed up, slow down, and even stop. But time cannot go backwards with an observer having knowledge of it. I want to keep it short, so the basic explanation that prevents backwards time travel is the Grandfather Paradox.

Slowing down time or speeding it up is relative to the observer, by the way. And ways to achieve this are by travelling considerably near the speed of light, or by entering a supermassive gravitational well. If you want to stop time, simply travel at the speed of light (this is impossible for humans), or pass through the event horizon of a black hole (which would most likely kill you). Just stick to very high speeds or gravitational wells.

 

[SelfSim]

It depends how you define "time travel".

I would say, from what you say below, that everything you say below is dependent on how you define 'time'.
Time is operationally defined in physics as being clock readings .. there is thus, no real need for it to be regarded as being any-'thing' beyond just that.

Otherwise, the only thing about time travel that is impossible would be backwards time travel. Time can speed up, slow down, and even stop. But time cannot go backwards with an observer having knowledge of it. I want to keep it short, so the basic explanation that prevents backwards time travel is the Grandfather Paradox.

Slowing down time or speeding it up is relative to the observer, by the way. And ways to achieve this are by travelling considerably near the speed of light, or by entering a supermassive gravitational well. If you want to stop time, simply travel at the speed of light (this is impossible for humans), or pass through the event horizon of a black hole (which would most likely kill you). Just stick to very high speeds or gravitational wells.

 

[Tinker Grey]

I time travel into the future at 1s/s.

 

[sjastro]

Could go all hypothetical here and suggest Krasnikov tubes(?)
(Paper here: A Superluminal Subway: The Krasnikov Tube)

AIUI, Krasnikov tubes are (hypothetical) ‘spacetime tunnels’ which allow for superluminal travel without violating causality, but only for round trips and with much larger energy requirements than say, the (hypothetical) Alcubierre drive.

I'm still trying to figure out the spacetime diagram for one, so I can't explain it yet .. any takers?:

View attachment 296553

Here is a brief description of your attached diagram.

The upper horizontal line is the space axis; the left hand thin vertical line is the time axis for the space-time diagram
The left hand thick vertical line represents the world line or trajectory in space-time of a point of departure (say Earth), the right hand thick vertical line is the destination.
Since the Earth’s orbit is very small compared to the width of the U shape it can be approximated to be spatially in the same position as is the point of destination.
As a result both the Earth and destination point are travelling vertically downwards as they are only moving in time and not in space.
The oblique line which forms the base of the U shape is the world line of a spaceship travelling from Earth to its destination inside the tube.

This is where things get complicated as light cones become distorted and tilted in gravitational fields.
I’ll use an example of a black hole.
In flat space-time the light cones have an undistorted shape and form 45⁰ angles in space-time diagrams as explained in my previous post.
In gravitational fields or using the equivalence principle in which a frame is being accelerated, the speed of light is no longer constant in accelerated frames and the light cones become distorted.

In this diagram the cylinder is a stationary black hole moving only in time.
The surface of the cylinder is the event horizon of the black hole, the vertical axis of the cylinder is the physical singularity.
At distances well away from the black hole, space-time is flat and the light cone is undistorted.
As photons approach the event horizon the light cones become progressively more distorted due to gravity.

For both black holes and a Krasnikov tube since travel is only possible into the future only the forward light cones are considered.
Outside the Krasnikov tube the forward light cones are not distorted as they are in flat space-time.
The two points outside the Krasnikov tube in the space-time diagram are the vertices of the undistorted forward light cones.

Without going into the maths inside the Krasnikov tube the light cones are distorted as illustrated.

I hope this clarifies your attached diagram which is a 180⁰ rotation of the axes when compared to the last diagram in my post.

 

[Bob Crowley]

I would say, from what you say below, that everything you say below is dependent on how you define 'time'.
Time is operationally defined in physics as being clock readings .. there is thus, no real need for it to be regarded as being any-'thing' beyond just that.

Due to your comment on "clock readings", I went looking for "time in physics" and got this Wikipedia article.

Time in physics - Wikipedia

I noticed this paragraph.

The caesium atomic clock became practical after 1950, when advances in electronics enabled reliable measurement of the microwave frequencies it generates. As further advances occurred, atomic clock research has progressed to ever-higher frequencies, which can provide higher accuracy and higher precision. Clocks based on these techniques have been developed, but are not yet in use as primary reference standards.

So I went looking for a picture of an atomic clock. After finding one, I decided to keep using the grandfather clock as our "primary reference standard", or I can just use a watch.

 

[SelfSim]

Due to your comment on "clock readings", I went looking for "time in physics" and got this Wikipedia article.

Time in physics - Wikipedia

I noticed this paragraph.
...
So I went looking for a picture of an atomic clock. After finding one, I decided to keep using the grandfather clock as our "primary reference standard", or I can just use a watch.

The higher 'accuracy' and 'precision' of those clocks permits finer grained measurements of the occurrence of events .. This does not mean they are getting closer to 'what time actually is'.
Horses for courses.

 

[Bob Crowley]

I was having a bit of a joke. I'm aware of the difference between the accuracy of the time we need to catch the 9.23 am to town, and the precision NASA might need to launch a Mars shot.

 

[jayem]

If time travel were possible, we’d know about it.

Absolutely. If it was possible, why haven't we been visited by anyone from the future?

 

[Abide with me.]

Think about it, if you for example use a strong magnet to speed things up in sort of an attempt to travel in time, people would notice and resist the changes, so only nature would change and speed up or go backwards, but I have the suspicion that the same would happen to nature also, that it would resist it, I wouldn`t go as far to say that energy is alive, but nature certainly is and sometimes when I pray for a god to exist, I think about something that I can`t really explain, a thing in nature, like an ore almost of something bright and living, so with this said, I suspect a little that time-travel itself is really close to impossible because there`s always something to resist it and it might prove that everything`s living, even materie

Stephen Hawking's threw a big party for all the people on the internet who claimed to be time travellers, but he didn't announce the date of the party till after the event.....nobody showed up!
However, that doesn't mean celestial beings don't have this power.....