[Chap]

There is this video clip on Youtube saying that its possible to make a "time machine", which it claims allows us to travel into the 'past' (not only back in time). I have given the link below:

http://www.youtube.c...h?v=oRWwI61so5Q

I see several flaws with this video, so please check whether my arguments are correct:

1)The video has been posted before it was confirmed that particles can indeed travel faster than the speed of light, so obviously they didn't have that information at the time. Viewing the video in that context: The argument of the coffee bean doesn't make much sense to me. I mean; when the coffee bean (or whatever) approaches the speed of light, its weight would approach infinity. Therefore, even all the energy in the stirring motion will not be sufficient to make the coffee bean move faster (since any practical engine will fail somewhere before infinity, no matter how close to infinity it can get).

2)I also can't quite understand how Blackholes allows us to go back into the past (not 'time'). Its reasonable to assume if a particle can go faster than light, then "time" will reverse itself for that particle, but how can that particle go back into the "past"? For example, let's say I step into a machine which can travel faster than light and I start travelling. Depending on how much faster than light I travel, "I" will get younger, while everything around me will get older, right? When I step out (say 2 seconds later), I would have grown younger than when I initially stepped into the machine, while everything else around me would have aged naturally. So I would have gone to the future (kind of), not into the past?

Please convey your ideas on this matter.
P.S physics is not my area of expertise, therefore forgive me for missing obvious details.

[morgsboi]

A time machine would be next to impossible but it would be possible to use relativity to our advantage. Orbiting around a black hole would slow down time around you so when you get back, your in the future relative to the black hole.

[DrRocket]

Chap, on 22 January 2012 - 01:58 AM, said:

There is this video clip on Youtube saying that its possible to make a "time machine", which it claims allows us to travel into the 'past' (not only back in time). I have given the link below:

http://www.youtube.c...h?v=oRWwI61so5Q

I see several flaws with this video, so please check whether my arguments are correct:

1)The video has been posted before it was confirmed that particles can indeed travel faster than the speed of light, so obviously they didn't have that information at the time. Viewing the video in that context: The argument of the coffee bean doesn't make much sense to me. I mean; when the coffee bean (or whatever) approaches the speed of light, its weight would approach infinity. Therefore, even all the energy in the stirring motion will not be sufficient to make the coffee bean move faster (since any practical engine will fail somewhere before infinity, no matter how close to infinity it can get).

2)I also can't quite understand how Blackholes allows us to go back into the past (not 'time'). Its reasonable to assume if a particle can go faster than light, then "time" will reverse itself for that particle, but how can that particle go back into the "past"? For example, let's say I step into a machine which can travel faster than light and I start travelling. Depending on how much faster than light I travel, "I" will get younger, while everything around me will get older, right? When I step out (say 2 seconds later), I would have grown younger than when I initially stepped into the machine, while everything else around me would have aged naturally. So I would have gone to the future (kind of), not into the past?

Please convey your ideas on this matter.
P.S physics is not my area of expertise, therefore forgive me for missing obvious details.

The situation is this:

There is nothing in general relativity per se that prohibits a time machine. Nevertheless no one believes that such a thing is possible.

Stephen Hawking has shown that under general relativity, with the additional assumption of the "weak energy condition" that no time machine is possible. He has also offered the "chronology protection conjecture" which posits that no time machine (closed timelike curve) is possible on the macroscopic scale.

The nature of quantum field theories is such that closed timelike curves might be possible at the level of elementary particles -- Feynman diagrams include such possibilities but they represent vanishingly small probabilities.

So, as it stands now, the chronology protection conjecture remains an open question. General relativity by itself will not answer the question. Quantum field theories indicate that a proof will likely involve considerations at the macroscopic level as distinct from the quantum level -- but there is no clear dividing line, so it will take greater understanding of physics than what is now available to answer the question with finality.

Nevertheless there are all sorts of paradoxes associated with the existence of time travel (closed timelike curves) that result in the nearly universal belief that time travel is not possible. There are still people who profess otherwise, mostly crackpots. I can guarantee that any representation of the possibility time travel on YouTube will fall into the crackpot category. YouTube, except for lectures by recognized scientists from recognized institutions, is not a good source for scientific information.

[ajb]

The best response right now is to say that it is not obvious why time machines are not permitted. Physicists who are trying to understand time machines are really interested in understanding general relativity and quantum field theory in the extreme. People are not usually really trying to send messages to themselves in the past, rather they want to push known theories to their limit in order to point towards new physics.

[Tres Juicy]

Chap, on 22 January 2012 - 01:58 AM, said:

1)The video has been posted before it was confirmed that particles can indeed travel faster than the speed of light, so obviously they didn't have that information at the time.

Unless the machine worked and they posted the video in the past

Seriously though, it hasn't been confirmed that anything can travel faster than c

[Chap]

Tres Juicy, on 23 January 2012 - 04:17 PM, said:

Unless the machine worked and they posted the video in the past

Seriously though, it hasn't been confirmed that anything can travel faster than c

ok, now I'm really confused!!! What was all the excitement about, if it was not confirmed that particles can indeed travel faster than c?

http://www.guardian....icles-neutrinos

[Tres Juicy]

Chap, on 24 January 2012 - 05:46 AM, said:

ok, now I'm really confused!!! What was all the excitement about, if it was not confirmed that particles can indeed travel faster than c?

http://www.guardian....icles-neutrinos

It's something that they are looking into, but it's not been confirmed.

There are a few different explanations going around

http://www.guardian....eutrinos-doubts

[The french tourist]

There's a simple reason that proves a time machine is not logically possible to be built (I'm not talking about scientific experiments). Assuming we manage to build a time machine, we would use it to go back in past. But if we went in the past, the local population would discover our machine. Therefore, it would have already been discovered in the past.

Another way of seeing it : if i said we won't be able to build a time machine before 2150, don't you think the scientists living in 2150 would have used their machine to go back at our time so that we would have discovered it ?

Hence, if humans were able to build such a machine, it would be a universal and non temporal machine every civilisations would know, which, obviously, is not the case.

[zapatos]

The french tourist, on 30 January 2012 - 07:06 PM, said:

There's a simple reason that proves a time machine is not logically possible to be built (I'm not talking about scientific experiments). Assuming we manage to build a time machine, we would use it to go back in past. But if we went in the past, the local population would discover our machine. Therefore, it would have already been discovered in the past.

But we did use it to go back in the past; to the year 2745. That is why we haven't seen it yet!

[Tres Juicy]

The french tourist, on 30 January 2012 - 07:06 PM, said:

There's a simple reason that proves a time machine is not logically possible to be built (I'm not talking about scientific experiments). Assuming we manage to build a time machine, we would use it to go back in past. But if we went in the past, the local population would discover our machine. Therefore, it would have already been discovered in the past.

Another way of seeing it : if i said we won't be able to build a time machine before 2150, don't you think the scientists living in 2150 would have used their machine to go back at our time so that we would have discovered it ?

Hence, if humans were able to build such a machine, it would be a universal and non temporal machine every civilisations would know, which, obviously, is not the case.

One of the theories is that you can only go back n the time frame where the time machine exists.

So if you invent the time machine in 2012 you can't go back to 2011

[MigL]

Say you lived in the year 2112 and you found, in your attic, the schematics for building a time machine drawn up by your great grand-father. So you build it and go back in time to our present, 2012, and discuss the idea of the time machine and its function with your great grand-father, who after you leave and return to 2112, draws up the schematics.

Who actually came up with the idea, or was the information just created ( I love these paradoxes ) ??

But seriously...
Say you and Kip Thorne have two wormhole generators and use thrm to estabilish a wormhole with the one opening at your end and the other in Kip Thorne's office. You then take your wormhole generator, hop aboard your spaceship and blast off to Proxima Centauri at an appreciable fraction of the speed of light, all the while conversing with Kip Thorne through your end of the wormhole. You descibe the sights to him and turn around and come back to Earth, still talking to Kip Thorne through the wormhole. Upon landing on Earth you find that although only acouple of years have passed for you, the Earth you have returned to has advanced thousands of years into the future and everyone you knew is long dead. 'No problem' says Kip thorne through the wormhole, 'Just step through the wormhole and return to the present'. So you do and have just travelled thousands of years into the past.

This is an example of a macroscopic closed time-like loop, and it involves way too many unproveable assumptions and unacheivable effects ( macroscopic wormholes ??? ) for my liking. But it hasn't stopped Kip Thorne ( physicist ) from exploring the possibility. Look him up, he has done some very interesting work with so called 'time travel'.

This post has been edited by MigL: 30 January 2012 - 11:15 PM

[morgsboi]

MigL, on 30 January 2012 - 11:15 PM, said:

Say you lived in the year 2112 and you found, in your attic, the schematics for building a time machine drawn up by your great grand-father. So you build it and go back in time to our present, 2012, and discuss the idea of the time machine and its function with your great grand-father, who after you leave and return to 2112, draws up the schematics.

It would be solved if you jumped onto an alternate timeline. That's how you can solve most time paradoxes.

[MigL]

Really ?
Alternate timeline or not, who came up with the original idea of the time machine ?

Causality violations cannot always be explaned away by 'alternate timelines'.

[DrRocket]

MigL, on 2 February 2012 - 12:06 AM, said:

Alternate timeline or not, who came up with the original idea of the time machine ?

Edward Page Mitchell ?

[Airbrush]

Read about the Montauk Project and you will wonder if it is possible.

MigL, on 2 February 2012 - 12:06 AM, said:

Really ?
Alternate timeline or not, who came up with the original idea of the time machine ?
Causality violations cannot always be explaned away by 'alternate timelines'.

H.G. Wells is probably the first true scifi writer. He wrote the original The Time Machine before 1895.

http://en.wikipedia....he_Time_Machine

This post has been edited by Airbrush: 2 February 2012 - 08:53 PM

[IM Egdall]

I like Hawking's point that there is empirical evidence time machines do not exist. He asks "where are all the tourists from the future visiting the present?"

This post has been edited by IM Egdall: 2 February 2012 - 09:13 PM

[MigL]

No, no, no...
I meant who came up with the idea for the time machine in my example of a paradox ( see previous post and response to Morgsboi ).

By the way, I certainly know who H.G. Wells is Airbrush, but you got me stumped Doc, who is E. P. Mitchell ?

[morgsboi]

MigL, on 2 February 2012 - 12:06 AM, said:

Really ?
Alternate timeline or not, who came up with the original idea of the time machine ?

Causality violations cannot always be explaned away by 'alternate timelines'.

They can because if there is an infinite amount of 'alternate timelines', there is an infinite amount of possibilities which means violations in our universe may not be violations in other universes.

[DrRocket]

MigL, on 2 February 2012 - 11:04 PM, said:

By the way, I certainly know who H.G. Wells is Airbrush, but you got me stumped Doc, who is E. P. Mitchell ?

http://en.wikipedia....d_Page_Mitchell

[ajb]

MigL, on 30 January 2012 - 11:15 PM, said:

Say you and Kip Thorne... .

I met Kip Thorne once, I took my niece who was about 10 at the time to a talk he gave on black holes. She remembers it fondly: if you fell into a black hole you get stretched until you get pulled apart. Strange how she thought the goriness of black holes was fascinating!

IM Egdall, on 2 February 2012 - 09:12 PM, said:

I like Hawking's point that there is empirical evidence time machines do not exist. He asks "where are all the tourists from the future visiting the present?"

There is some mathematical/theoretical evidence that time machines are not allowed by nature. In particular, there are results that suggest that quantum field theory near a time machine is "sick". These results are based on semi-classical gravity, which is quantum field theory on curved backgrounds. The space-time is classical and thus described by Einstein's general relativity but the fields (apart from gravity) are described using quantum field theory.

However, quantum field theory on curved backgrounds is a very difficult subject and not as well posed or as easy to interpret as quantum field theory on Minkowski space-time. So I would certainly claim, that despite what we know about semi-classical gravity it is still not really clear if nature fully disallows time machines.