Interesting article but I don't believe a word of it.  Traveling back in time means resurrecting people who are long dead.  How do you do that?  Maybe resurrecting vision of the past from light waves that are still travelling through the universe might be theoretically possible actually walking through a city like San Francisco in 1906 and experiencing the earthquake and shaking hands with people who have turned to dust is inconceivable to me.  It means more than just travelling to the past.  It means reconstructing the past.  The people...the infrastructure...the geography...the events and their causes.

https://interestingengineering.com/science/time-machine-using-lasers

Noel

 

The "Grandfather paradox" is on this.

9 hours ago, birdguy said:

Interesting article but I don't believe a word of it. 

I am pretty much allergic to movies about time travel, they always toy with the nonsensical idea that you could change your own past. Having said that, there are two ways how time travel may be logically possible: (i) if everything we do is pre-determined and time travel is supposed to happen, as part of a grander scheme; (ii) if everything repeats itself, like in the groundhog day movie. I personally don't believe in either of the two possibilities.

The article and the research that you posted are actually reasonable, but one has to be careful in understanding what he is trying to do. He is building a toy model of a black hole. That idea is around for about 20 years and uses the fact that light travels through spacetime in a similar way as it travels through optical materials (like prisms, lenses, mirrors etc). The equations are the same, but the physics is very different. I remember vividly how a journalist in a notable magazine was extremely concerned back then. He believed scientists wanted to create a black hole in the lab, which, in his view, could swallow the Earth. Nothing like this will happen, they are just stirring gases or fluids, it is completely harmless. In fact, it has already been done ( https://en.wikipedia.org/wiki/Sonic_black_hole ).

It is conceivable that this guy can create a toy-like time travel in his optical model. However, that would just mean that a wave travels backwards in a gas or a fluid, at a speed that is much slower than the speed of light in vacuum. To do the same in real space and time would require exotic forms of energy (e.g., energy extracted from a vacuum). Most experts believe that it is not possible to do that. So, sorry, no resurrecting will be possible.

Peter

13 hours ago, birdguy said:

It means reconstructing the past.

It's not reconstructing the past. The past is preserved in the "time line", which is like a continuous recording of the existence of everything. 

So, it's a bit like a movie where you start watching at a certain point in the movie which represents your time of existence. If you could rewind the movie to an earlier scene, you would see what happened at that point in time. It doesn't have to be reconstructed because it always exists unchanged.

 

13 hours ago, birdguy said:

Interesting article but I don't believe a word of it.  Traveling back in time means resurrecting people who are long dead.  How do you do that?

 

Thing is, we don't understand then true nature of time, why it flows. There are scientists like Carlo Rovelli that believe time, as we perceive it, is an illusion.

Albert wrote... 

 

Quote

Albert Einstein once wrote: People like us who believe in physics know that the distinction between past, present and future is only a stubbornly persistent illusion. Time, in other words, he said, is an illusion. Many physicists since have shared this view, that true reality is timeless.

 

There as a concept called "Block Time".

 

Quote

Block time is all of time – the past, present and future – existing in a four-dimensional block of spacetime known as a block universe. If we live in a block universe, our perception of time as only ever moving forward at a steady rate is just an illusion, a "mathematical artefact of the physics".

 

https://plus.maths.org/content/why-block-time#:~:text=Block time is all of,mathematical artefact of the physics".

 

Quote

 

A block universe

When Einstein unified space and time in his general theory of relativity in 1915, he gave us a new way to picture our Universe. "Imagine a regular chunk of cement," says Marina Cortês, a cosmologist from the Royal Observatory, Edinburgh. "It has three dimensions but we live in four dimensions: the three spatial dimensions plus one time dimension. A block universe is a four-dimensional block, but instead of [being made of cement, it is made of] spacetime. And all of the space and time of the Universe are there in that block."

We can't see this block, we're not aware of it, as we live inside the cement of spacetime. And we don't know how big the block universe we live in is: "We don't know if space is infinite or not. Or time - we don't know whether it has a beginning or if it will have an end in the future. So we don't know if it's a finite chunk of spacetime or an infinite chunk."

 

https://plus.maths.org/content/what-block-time

 

Imagine a layer cake. The cake has three dimensions, but we need to pretend that the fourth dimension of time is the layers, all of space and time are present within the cake. The past, the future, the present, all exist, just not where you are now, now is just the present. 

 

Edited March 5, 20233 yr by martin-w

 

He's talking about a gravitational field that he believes could lead to loops in time. He believes that rapidly rotating laser light can generate gravity and as we know, gravity influences time, thus, laser light itself can influence time. He's talking about the spacetime  in-between his circular laser light being twisted. He obviously hasn't got the intensity high enough tp achieve his aim, but he believes the equations tell him its possible. The objections are that the experiment might need to be the size of the universe, or as much energy as required to form a black hole.  

 

 

 

Edited March 5, 20233 yr by martin-w

5 hours ago, Wildblue said:

The "Grandfather paradox" is on this.

 

Unless, when you travel back in time and kill your grandfather, no paradox ensues. Because you simply generate a new separate time line, and when you return to your time line, all is as you left it. 🤔

1 hour ago, martin-w said:

 

He's talking about a gravitational field that he believes could lead to loops in time. He believes that rapidly rotating laser light can generate gravity and as we know, gravity influences time, thus, laser light itself can influence time. 

Thanks for posting that. I should watch videos before commenting on it 😜

What I wrote above refers to an entirely different experiment, which has been performed and is pretty cool. However, that guy with his laser beams is pretty naïve. The energy density of even the strongest laser beams is far (!!) too small to have any sizeable effect on time. 

1 hour ago, qqwertzde said:

The energy density of even the strongest laser beams is far (!!) too small to have any sizeable effect on time. 

 

Yep. The objections are that the experiment might need to be the size of the universe, or as much energy as required to form a black hole.  

I think Mallett knows this. He's just doing the preparatory work ready for when we are a Kardashev Type 3 civilization. 😁

 

The idea of time travel is based on model of the universe offered by physicist. Although sophisticated and capable of making precise prediction about the state of "now" in a system after a predetermined period has elapsed it is still not even close to being a virtual replica of reality and it never will be. It is so far off that the difference between how far off modern physics is compared to how far off classical physics is, is negligible. One might say that modern physics is in as deep or deeper a crisis than classical physics was after the Michelson Morley experiment. But having said that time travel is ridiculous because you cannot go to a place that doesn't exist. There is one exception. It is 5:35pm PM on Sunday. I intend to travel through space and time to arrive at 5:35pm on Monday. I predict the journey is going to take me exactly 24 hours.

I think I better say nothing about that 😕

1 hour ago, qqwertzde said:

I think I better say nothing about that 😕

Ah go on! Where's the fun in that!🤣

Edited March 6, 20233 yr by FBW737

6 hours ago, FBW737 said:

One might say that modern physics is in as deep or deeper a crisis than classical physics was after the Michelson Morley experiment.

 

One might not say that. Physics as a whole is not in a state of crisis. 

The crisis exists, but its in terns of physics that deals with fundamental particles and fields. Its a subset of physics.

6 hours ago, FBW737 said:

 time travel is ridiculous because you cannot go to a place that doesn't exist. 

 

Unless it does exist.

https://plus.maths.org/content/what-block-time#:~:text=We can't see this,an end in the future.

 

Time is an illusion

"So if the future and past are already encoded into the block universe we inhabit – how does that account for our human experience of life, of our inexorable movement through time?

From this block time perspective, time, as we experience in the block universe, is an illusion. "It's not a real, fundamental property of nature," says Cortês. The ticking of time, our experience of time passing, is only because we are stuck inside the block universe, moving forward along the dimension of time. "The fact that we experience moving forward in the block but not outside it comes from the fact that the block picture treats time just as another spatial dimension, and we can step outside of it. Time is not pervasive."

This leads to fundamental questions that cosmologists today are addressing in their theories describing the nature of our Universe. If our Universe is like this block universe, then everything – past and future – has happened and our experience of time is just a mathematical artefact arising from the equations describing the Universe. "

Edited March 6, 20233 yr by martin-w

17 hours ago, martin-w said:

 

Unless, when you travel back in time and kill your grandfather, no paradox ensues. Because you simply generate a new separate time line, and when you return to your time line, all is as you left it. 🤔

O was the Grandfather paradox not about when you kill your grandfather he can't have made your father and your father can't have made you so you immediately cease to exist?