Does Einstein's Theory of Relativity Substantiate the idea of Time Travel?

[CPSU012]

Ronald Mallett, PhD is a renowned physicists known for his proponents on the idea of time travel. Mallett uses his background in physics and mathematics to support his idea to build a time machine, using Einstein's Theory of Relativity as a basis.
Do you think this is even possible? Right now, Mallett is testing and measuring the speeds of neutrons in light beams in attempts to create a valid and working time machine within the next ten years.

 

[abhishek ghos]

we can't travel through it, fit for smaller particles, quantum particles

 

[LostConjugate]

Yes, time travel is possible and personal time machines have already been around since the early 1900's. Many people have one in their garage. The problem is it takes a lot of energy to go very far into the future and relativity suggests there is no way around this.

 

[DrChinese]

Ronald Mallett, PhD is a renowned physicists known for his proponents on the idea of time travel. Mallett uses his background in physics and mathematics to support his idea to build a time machine, using Einstein's Theory of Relativity as a basis.
Do you think this is even possible? Right now, Mallett is testing and measuring the speeds of neutrons in light beams in attempts to create a valid and working time machine within the next ten years.

Welcome to PhysicsForums, CPSU012!

I think the simple answer is that a time machine is not feasible by most notions of the word feasible. Even a single quantum particle being transported through time is far-fetched in my book, as I have no idea how you would demonstrate such other than by making questionable assumptions.

 

[JesseM]

Ronald Mallett, PhD is a renowned physicists known for his proponents on the idea of time travel. Mallett uses his background in physics and mathematics to support his idea to build a time machine, using Einstein's Theory of Relativity as a basis.
Do you think this is even possible? Right now, Mallett is testing and measuring the speeds of neutrons in light beams in attempts to create a valid and working time machine within the next ten years.

Why did you post this in the quantum physics forum rather than the relativity forum? Einstein's theory of general relativity does have some solutions which allow backwards time travel, like traversable wormholes, although a theorem by Stephen Hawking shows that in order to create a time machine in a finite region of space certain energy conditions must be violated, and although physicists argue that quantum effects like the Casimir effect may do this, it's unclear whether these quantum effects will violate all the necessary conditions (see this section of wikipedia's wormhole article). Also, some calculations suggest that vacuum fluctuations looping back and forth through time would build up and cause the energy density to approach infinity on the boundary of a region of spacetime allowing time travel (the boundary is technically called a Cauchy horizon), which probably means we can't really understand what's going on there without a theory of quantum gravity, and that perhaps such a theory will satisfy Hawking's chronology protection conjecture and rule out the possibility of backwards time travel entirely. A good discussion of these issues can be found in Kip Thorne's book https://www.amazon.com/dp/0393312763/?tag=pfamazon01-20.

As for Ronald Mallett, I think there are a lot of good reasons to suspect that his arguments about why he thinks his experiment might allow time travel are seriously flawed, see the Objections section of his wikipedia article.

 

[LostConjugate]

Why did you post this in the quantum physics forum rather than the relativity forum? Einstein's theory of general relativity does have some solutions which allow backwards time travel, like traversable wormholes, although a theorem by Stephen Hawking shows that in order to create a time machine in a finite region of space certain energy conditions must be violated, and although physicists argue that quantum effects like the Casimir effect may do this, it's unclear whether these quantum effects will violate all the necessary conditions (see this section of wikipedia's wormhole article). Also, some calculations suggest that vacuum fluctuations looping back and forth through time would build up and cause the energy density to approach infinity on the boundary of a region of spacetime allowing time travel (the boundary is technically called a Cauchy horizon), which probably means we can't really understand what's going on there without a theory of quantum gravity, and that perhaps such a theory will satisfy Hawking's chronology protection conjecture and rule out the possibility of backwards time travel entirely. A good discussion of these issues can be found in Kip Thorne's book Black Holes and Time Warps.

As for Ronald Mallett, I think there are a lot of good reasons to be skeptical that his arguments about why he thinks his experiment might allow time travel are seriously flawed, see the Objections section of his wikipedia article.

I think there is some mis-interpretation of the reverse time travel solutions. If it even is possible.

Say you want to see what the world was like in the past. You would not want to enter the worm hole, you would want to find a nice safe location in space and throw the entire Earth into the worm hole, since it is the Earth that you want to travel back in time, not yourself.

In the case of traveling to the future, you simply need to temporarily create a relative time difference at which your own mind and body operate, which is easily done by traversing reference frames.

 

[JesseM]

I think there is some mis-interpretation of the reverse time travel solutions. If it even is possible.

Say you want to see what the world was like in the past. You would not want to enter the worm hole, you would want to find a nice safe location in space and throw the entire Earth into the worm hole, since it is the Earth that you want to travel back in time, not yourself.

The object that travels back in time through the wormhole doesn't age in reverse! If you travel into a wormhole your own proper time increases (you get older) between the time you enter one mouth and the time you exit the other, the idea of time travel is that the region of spacetime where you exit one mouth could in theory be within the past light cone of the region where you entered the other mouth.

 

[LostConjugate]

The object that travels back in time through the wormhole doesn't age in reverse! If you travel into a wormhole your own proper time increases (you get older) between the time you enter one mouth and the time you exit the other, the idea of time travel is that the region of spacetime where you exit one mouth could in theory be within the past light cone of the region where you entered the other mouth.

I am not sure the physical meaning of the past light cone is well understood. I do not think it is actually the state of all particles in the universe as it was in the past.

 

[JesseM]

I am not sure the physical meaning of the past light cone is well understood. I do not think it is actually the state of all particles in the universe as it was in the past.

It seems like you haven't really studied relativity, this is pretty basic: the past light cone of some event E is defined as the set of events in the past that could have sent a signal (moving at the speed of light or slower) which would be able to reach the position and time of E.

 

[ghwellsjr]

Ronald Mallett, PhD is a renowned physicists known for his proponents on the idea of time travel. Mallett uses his background in physics and mathematics to support his idea to build a time machine, using Einstein's Theory of Relativity as a basis.
Do you think this is even possible? Right now, Mallett is testing and measuring the speeds of neutrons in light beams in attempts to create a valid and working time machine within the next ten years.

Don't you think that if Mallett is correct that he could build a time machine within the next ten years, he would have already come back to our time with his solution so that we wouldn't have to wait ten years?

 

[GrayGhost]

I seen Dr Ronald Mallett's pitch before. In fact, a few years ago. He does not plan to send people back in time. He intends to use light beams to drag spacetime, then send particles of encoded information back in time. By his theory, the information can only go back (at most) as far as when he first turned on his machine, and had the receiver working. IOWs, one day he hopes he will receive a signal from the future. That can happen only after he first gets the system, the transmitter, and the reciever all working ... and he never knows until it "just happens" that he's successfull. I figure he'll be sending Lotto numbers back everyday until it works.

GrayGhost

 

[LostConjugate]

It seems like you haven't really studied relativity, this is pretty basic: the past light cone of some event E is defined as the set of events in the past that could have sent a signal (moving at the speed of light or slower) which would be able to reach the position and time of E.

But how can one person go through a worm hole and cause all particles in the entire universe to re-arrange themselves into some state they were all in in the past. What if two people go through two different worm holes, which person does the universe appeal to?

So you can't really talk about the past light cone as a place just 1 object can travel to. It is a state of the entire universe.

 

[JesseM]

But how can one person go through a worm hole and cause all particles in the entire universe to re-arrange themselves into some state they were all in in the past. What if two people go through two different worm holes, which person does the universe appeal to?

The universe doesn't have to re-arrange itself, you have to think in terms of relativity's view of time as a dimension in a 4-dimensional spacetime manifold, with all object's histories represented as frozen worldlines within this 4D spacetime. Something I wrote about this in a [post=424998]post[/post] long ago:

In both special and general relativity, you have to get rid of the idea of a single universal present, since these theories say that different observers have different views of whether two different events happened "at the same time" or not, and each observer's reference frame is equally valid. So instead you have to think of a single static 4-dimensional "spacetime" which contains the entire history of the universe; traveling back in time in this context means that an object's "worldline" curves back on itself and revisits a region of spacetime it already crossed through before.

Think of a block of solid ice with various 1-dimensional strings embedded in it--if you cross-section this block, you will see a collection of 0-dimensional points (the strings in cross-section) arranged in various positions on a 2-dimensional surface, and if you take pictures of successive cross-sections and arrange them into a movie, you will see the points moving around continuously relative to one another (in terms of this metaphor, the idea that there is no single universal present means you have a choice of what angle to slice the ice when you make your series of cross-sections). You shouldn't think of time travel as the points returning to precisely the same configuration they had been in at an earlier frame of the movie; instead, you should just imagine one of the strings curving around into a loop within the 3-dimensional block, what in general relativity is known as a "closed timelike curve".

 

[CPSU012]

I understand these concepts in a scientific sense in that, on paper, they seem conceivable. The mathematics and physics of time travel sound plausible, but thinking about it as in a person's ability to retrace history and end up in a place and time which has already occurred for everyone else- just seems like it is not possible. I think Mallett makes some valid points concerning the equational side of his theories, but I don't know about the traveling itself. As for traveling into the future, isn't that just missing the time between this point and that point (now to the place you ''travel'' to)?
I watched this video recently and listened thoroughly to Mallett's ideas. I value his opinions on travel, but am afraid to be a believer in it without evidential and experimental truth.

 

[LostConjugate]

The universe doesn't have to re-arrange itself, you have to think in terms of relativity's view of time as a dimension in a 4-dimensional spacetime manifold, with all object's histories represented as frozen worldlines within this 4D spacetime. Something I wrote about this in a [post=424998]post[/post] long ago:

I like the 4-space approach, though time is not exactly the same as the spatial coordinates in this point of view. The time coordinate is only there to give us something to compare momentum of all objects to, therefore it must have constraints, such as only positive derivatives with respect to any of the spatial coordinates.

 

[bobc2]

The universe doesn't have to re-arrange itself, you have to think in terms of relativity's view of time as a dimension in a 4-dimensional spacetime manifold, with all object's histories represented as frozen worldlines within this 4D spacetime. Something I wrote about this in a [post=424998]post[/post] long ago:

Very nice way to explain the situation.