↑Time to resurrect the latest professional expert opnion, in light of the nonsensical rubbish that is being posted of late from Farsight and MD.
Billy T said.......
I don't think it is "time travel" any more than other means actually available* to some small extent now that slow one's rate of aging as measured by clocks on earth. Yes conceptually it is possible by accelerating for a few years at the few Gs max the body can tolerate for more than an hour, so you could in principle live to die 200 years by earth's clocks after your birth, but actually being the "traveling twin" to do that probable would cost more than a year of the world's total GDP, so will not be done, even if technically possible.
Much more probable of actually being done is learning the detail of how bears do hibernate for many months and some of that knowledge being applied to humans so they can live to see their great, great grand children and the nature of the world that will exist then. Or an application of that knowledge may be government financed to reduce the food and other cost of colonizing Mars, etc.
In both cases no one is Traveling into a future that does not yet exist. We all are Traveling into future as it becomes the present. But via space ships or suspended animation, one can live longer or "age more slowly" by Earth's clocks.
I have asked you before if you call suspended animation "time travel" - no reply yet, but I'll wait. There is no logical or rational reason I can see /understand why only one of these two methods of slowing the aging process should be called "time travel" and not the other. If you can tell me one, please do.
It is not that the laws of physics do not prohibit time travel (or dozen of the other concepts in science fiction) - it is the simple fact that
there is no where to travel too as neither the future or the past exists ANYWHERE now. One once did and the other some day will be our "now." The laws of physics do not prohibit travel to the apex of a sphere. - What prohibits that is that there is nowhere an apex of a sphere to travel to.
* The drugs inducing coma and lowering whole body temperature as used mainly with brain and open heart replacement surgery, which takes most of a day to do.
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paddoboy said........
That's your opinion and one in general not shared by most physicists today.
It is a relevant fact despite your objections that .....
TIME TRAVEL IS NOT FORBIDDEN BY THE LAWS OF PHYSICS AND GR:
I have said that many times now, and I'll say it as often as it seems necessary to say...
Theoretically time travel could be achieved by
[1] Time dilation effects as already mentioned.
[2]Alcubierre Drive type of arrangement in line with Einstein's field equations in GR.
[3] Worm hole:
[4] My own speculative scenario is by means of manipulation of the Higgs particle and field, to reflect a perception of "no mass" and so be able to achieve FTL travel.
All difficult, all uncertain, and all beyond present technological capabilities, but all would be achievable by any sufficiently advanced civilisation, as the laws of physics and GR do not forbid it.
The only thing factual in this thread is the title that "time travel is science fiction" is certainly correct at this time in our advancement.
But that could and may change in the near or distant future.
Prof. Alcubierre said:
Hi, thanks for the message.
What "Billy" says is not correct. According to General Relativity, the future and past do exist. In fact, there is no absolute way to define "the present" except at a single point. Simultaneity is relative, it depends on the observer. When we solve the Einstein equations we obtain the whole spacetime, past and future included. We normally call this a "block Universe".
About time travel, it is well known that travelling to the future is possible, essentially because of the time dilation effects. If you travel very fast and come back you will have aged less that the people that stayed behind. Travelling close to light speed for a long time and coming back could allow you to experience a short time (say a few years) and come back when millennia have gone by on Earth. Similarly, gravity also produces time dilation, so you could stay close in orbit to a large black hole for a few years and again come back to find millenia have gone by on Earth.
Travelling to the past is a different matter. There are several ideas that have been proposed within relativity to achieve this:
1) Travelling faster than light. If you could travel faster than light you would be travelling to the past as seen by some observers. You could in principle use this to travel back in time. Hypothetical particles called "tachyons" are supossed to be able to do this, but as far as we know they don't exist. You could certainly use my "warp drive" to do the exact same thing, again assuming it is possible.
2) Wormholes could allow you not just to travel to a distant place, but also back in time. Again, this depends on wormholes existing in the first place, and second on the laws of physics allowing time travel.
The idea of the "Higgs" field makes no sense. It is not a matter of speculating with words, one needs to do the math. As far as I know there is no way to use a Higgs field to travel back in time.
But ... Travelling back in time violates causality, causes a series of logical paradoxes, and means that we loose all predictability. There are good reasons to believe it is therefore impossible. Hawking has argued quite strongly saying that the final laws of physics will probably prohibit time travel to the past. His arguments are very strong, but they are not a proof. Still, my guess is that he is probably right.
Time to resurrect the latest professional expert opnion, in light of the nonsensical rubbish that is being posted of late from Farsight and MD.
