12 ms·

Traveling back in time could be possible

56 points by jurjenh 9y ago

smallnamespace 9y ago
Note that under our current understanding of General Relativity, wormholes will rapidly collapse under their own gravity so quickly that not even a single photon would be able to traverse it because it closes off. There's a theoretical way to stabilize it: put 'exotic matter' in the middle. Unlike all other matter, exotic matter has a negative energy density. This is the same sort of matter that would be needed to create an Alcubierre warp drive. Unfortunately, we don't have any idea how to go about creating exotic matter. The closest we've come is the Casimir effect, when a region between two very close conductive plates will in some ways act as if there were negative energy. [1] http://www.bibliotecapleyades.net/ciencia/negativeenergy/negativeenergy.htm http://www.bibliotecapleyades.net/ciencia/negativeenergy/neg...
- samstave 9y ago
  This is such a fascinating comment - can you please give me an ELI5 out-of-the-loop comment to help me understand
- yarg 9y ago
  Just a quibble, you are referring here to a form of matter with a specific exotic property, which is not a property necessarily held by all forms of exotic matter.
- dwaltrip 9y ago
  TLDR: theoretically possible with hypothetical extrapolations of existing physics, but incredibly unlikely that the needed extrapolations are both possible and viable for use by humans
- sullyj3 9y ago
  > Unfortunately, we don't have any idea how to go about creating exotic matter A priori, I don't see any reason to believe that creating it should be possible. It's never been observed, and I'm assuming there aren't any models which predict any methods by which it might come into existence. That's as good as saying it's made up to me.
MiddleEndian 9y ago
I broke my rule of not reading medium articles, but how exactly does this prevent the grandfather paradox? Once you're back in time you can still stop yourself in the future from entering the worm hole...
- ricardobeat 9y ago
  You'd need to physically catch up to yourself (your parents, in the case) which is impossible given they are traveling at the speed of light, in chase of the other end of the wormhole. At least that's what I could gather.
  - MiddleEndian 9y ago
    Wouldn't another wormhole going the other way allow you to get around this?
  - pavel_lishin 9y ago
    Why not send the wormhole on a circular journey? Accelerate out, decelerate, accelerate back, decelerate. Enjoy two relativistic trips, and end up parked side-by-side. This is the mechanism Stephen Baxter used in his Xeelee sequence novels.
- pavel_lishin 9y ago
  Where's the paradox? Given that a person has already appeared out of nowhere - matter/energy has been created - I'd say that having someone with identical genetic make-up to them running around is minor stuff.
  - MiddleEndian 9y ago
    I exist in 2017. I go to 1978. I kill my other form before 2017 is reached. Therefore I cannot have traveled to 1978. What has occurred at each particualy moment is no longer consistent in a way that is clearly comprehensible by humans.
    - 9y ago
pfarnsworth 9y ago
I don’t see how time travel doesn’t violate the law of conservation of energy or conservation of mass. That seems pretty fundamental to me, so it would require converting an extremely large amount of energy into the mass that is going back in time.
- Gravityloss 9y ago
  What if you can only send and receive information?
wallace_f 9y ago
It seems we have laws of physics covering everything from Newtonian mechanics, relativity and quantum mechanics... Is there any law stating time travel must go one direction? Has it ever been proposed?
- BlaXpirit 9y ago
  Second law of thermodynamics https://en.wikipedia.org/wiki/Entropy_(arrow_of_time) https://en.wikipedia.org/wiki/Entropy_(arrow_of_time)
  - matt_wulfeck 9y ago
    >The Second Law of Thermodynamics states that the state of entropy of the entire universe, as an isolated system, will always increase over time My understanding (which is very small) is that the multiverse theory takes care of not violating this law, since it’s not an isolated system.
    - PhilWright 9y ago
      And....there is no evidence at all that there is another Universe other than ours. Once you have proven the existence of a multiverse we can then take theories that require it seriously. Until then it is pure fantasy.
deleted 9y ago
[deleted]
rurban 9y ago
Theoretically yes, but what they didn't tell you is that all those particles travelling through will completely lose all their information and order how they belong together. So please dear sci-fi authors stop with these ridiculous plots.
- dailyvijeos 9y ago
  Thank you. These filler, lazy articles are mental masturbation clickbait for people whom are dazzled by the illusions of perpetual motion, FTL, transmutation, cold fusion, snake oil and get rich quick schemes.
matt_wulfeck 9y ago
The real question I have is how would you ever stabilize something as powerful as a black hole.
- ssijak 9y ago
  universe> ssh god@blackhole-42 universe@backhole-42> configure universe@backhole-42> set stable MAX_VALUE universe@backhole-42> commit ..changes successfully committed to blackhole-42 universe@backhole-42> exit universe>
alistproducer2 9y ago
If I read that correctly, you are never able to travel back further than the creation of the wormhole.
- sullyj3 9y ago
  Sounds like the movie Primer
snissn 9y ago
> If this negative mass/energy matter exists
hanoz 9y ago
Travelling backwards in time is not possible, it's obviously not possible, and it's a wonder that the idea gets given such credence in educated circles, apart from it being a nice thought and a diverting intellectual exercise.
- Shikadi 9y ago
  Actually, time travel is real. My name is John Titor, from the year 2036. I'm looking for an old IBM 5100, does anyone here know where I can find one? The future of the world depends on it!
true_tuna 9y ago
Once
SolarNet 9y ago
It's not clear what all the rules are and how this prevents the grandfather paradox. What ever mechanism that prevents the paradoxical violations also makes this not very exciting (as far as time travel goes): you have to spend the "40 years" between you visiting one end of the wormhole and you entering the other at near-luminal velocity (hence you would only perceive it as 1 anyway). It's not so much "time travel" as an instant return ticket (where only your personal real time is spent, assuming your ship is exactly as fast as the one that carried the wormhole). Which does actually have an interesting effect if you make them in pairs. It makes books like The Commonwealth Saga technically almost viable (e.g. where they build networks of portals and then just run trains through them non-stop to travel between worlds). Except that instead of using portals to explore new worlds, they would have to send a probe to those planets with a wormhole on board, at near the speed of light. And trips might cost you a bit of relative time to make a trip and return (e.g. the difference between the speed of light and the speed the probe delivered the wormhole from both portals added together would be how far in the relative future a trip would send you). This all of course requires exotic matter which probably doesn't exist; which is why this whole thing probably doesn't work in the first place (e.g. why stable wormholes probably don't exist). Still might make it's own excellent sci-fi book if someone ran with the constrains of this, and it would technically be harder sci-fi than most.

56 points by jurjenh 9y ago

Note that under our current understanding of General Relativity, wormholes will rapidly collapse under their own gravity so quickly that not even a single photon would be able to traverse it because it closes off. There's a theoretical way to stabilize it: put 'exotic matter' in the middle. Unlike all other matter, exotic matter has a negative energy density. This is the same sort of matter that would be needed to create an Alcubierre warp drive. Unfortunately, we don't have any idea how to go about creating exotic matter. The closest we've come is the Casimir effect, when a region between two very close conductive plates will in some ways act as if there were negative energy. [1] http://www.bibliotecapleyades.net/ciencia/negativeenergy/negativeenergy.htm http://www.bibliotecapleyades.net/ciencia/negativeenergy/neg...

samstave 9y ago
This is such a fascinating comment - can you please give me an ELI5 out-of-the-loop comment to help me understand
yarg 9y ago
Just a quibble, you are referring here to a form of matter with a specific exotic property, which is not a property necessarily held by all forms of exotic matter.
dwaltrip 9y ago
TLDR: theoretically possible with hypothetical extrapolations of existing physics, but incredibly unlikely that the needed extrapolations are both possible and viable for use by humans
sullyj3 9y ago
> Unfortunately, we don't have any idea how to go about creating exotic matter A priori, I don't see any reason to believe that creating it should be possible. It's never been observed, and I'm assuming there aren't any models which predict any methods by which it might come into existence. That's as good as saying it's made up to me.

MiddleEndian 9y ago

I broke my rule of not reading medium articles, but how exactly does this prevent the grandfather paradox? Once you're back in time you can still stop yourself in the future from entering the worm hole...

ricardobeat 9y ago
You'd need to physically catch up to yourself (your parents, in the case) which is impossible given they are traveling at the speed of light, in chase of the other end of the wormhole. At least that's what I could gather.
- MiddleEndian 9y ago
  Wouldn't another wormhole going the other way allow you to get around this?
- pavel_lishin 9y ago
  Why not send the wormhole on a circular journey? Accelerate out, decelerate, accelerate back, decelerate. Enjoy two relativistic trips, and end up parked side-by-side. This is the mechanism Stephen Baxter used in his Xeelee sequence novels.
pavel_lishin 9y ago
Where's the paradox? Given that a person has already appeared out of nowhere - matter/energy has been created - I'd say that having someone with identical genetic make-up to them running around is minor stuff.
- MiddleEndian 9y ago
  I exist in 2017. I go to 1978. I kill my other form before 2017 is reached. Therefore I cannot have traveled to 1978. What has occurred at each particualy moment is no longer consistent in a way that is clearly comprehensible by humans.
  - 9y ago

pfarnsworth 9y ago

I don’t see how time travel doesn’t violate the law of conservation of energy or conservation of mass. That seems pretty fundamental to me, so it would require converting an extremely large amount of energy into the mass that is going back in time.

Gravityloss 9y ago
What if you can only send and receive information?

wallace_f 9y ago

It seems we have laws of physics covering everything from Newtonian mechanics, relativity and quantum mechanics... Is there any law stating time travel must go one direction? Has it ever been proposed?

BlaXpirit 9y ago
Second law of thermodynamics https://en.wikipedia.org/wiki/Entropy_(arrow_of_time) https://en.wikipedia.org/wiki/Entropy_(arrow_of_time)
- matt_wulfeck 9y ago
  >The Second Law of Thermodynamics states that the state of entropy of the entire universe, as an isolated system, will always increase over time My understanding (which is very small) is that the multiverse theory takes care of not violating this law, since it’s not an isolated system.
  - PhilWright 9y ago
    And....there is no evidence at all that there is another Universe other than ours. Once you have proven the existence of a multiverse we can then take theories that require it seriously. Until then it is pure fantasy.

deleted 9y ago

[deleted]

rurban 9y ago

Theoretically yes, but what they didn't tell you is that all those particles travelling through will completely lose all their information and order how they belong together. So please dear sci-fi authors stop with these ridiculous plots.

dailyvijeos 9y ago
Thank you. These filler, lazy articles are mental masturbation clickbait for people whom are dazzled by the illusions of perpetual motion, FTL, transmutation, cold fusion, snake oil and get rich quick schemes.

matt_wulfeck 9y ago

The real question I have is how would you ever stabilize something as powerful as a black hole.

ssijak 9y ago
universe> ssh god@blackhole-42 universe@backhole-42> configure universe@backhole-42> set stable MAX_VALUE universe@backhole-42> commit ..changes successfully committed to blackhole-42 universe@backhole-42> exit universe>

alistproducer2 9y ago

If I read that correctly, you are never able to travel back further than the creation of the wormhole.

sullyj3 9y ago
Sounds like the movie Primer

snissn 9y ago

> If this negative mass/energy matter exists

hanoz 9y ago

Travelling backwards in time is not possible, it's obviously not possible, and it's a wonder that the idea gets given such credence in educated circles, apart from it being a nice thought and a diverting intellectual exercise.

Shikadi 9y ago
Actually, time travel is real. My name is John Titor, from the year 2036. I'm looking for an old IBM 5100, does anyone here know where I can find one? The future of the world depends on it!

true_tuna 9y ago

Once

SolarNet 9y ago

It's not clear what all the rules are and how this prevents the grandfather paradox. What ever mechanism that prevents the paradoxical violations also makes this not very exciting (as far as time travel goes): you have to spend the "40 years" between you visiting one end of the wormhole and you entering the other at near-luminal velocity (hence you would only perceive it as 1 anyway). It's not so much "time travel" as an instant return ticket (where only your personal real time is spent, assuming your ship is exactly as fast as the one that carried the wormhole). Which does actually have an interesting effect if you make them in pairs. It makes books like The Commonwealth Saga technically almost viable (e.g. where they build networks of portals and then just run trains through them non-stop to travel between worlds). Except that instead of using portals to explore new worlds, they would have to send a probe to those planets with a wormhole on board, at near the speed of light. And trips might cost you a bit of relative time to make a trip and return (e.g. the difference between the speed of light and the speed the probe delivered the wormhole from both portals added together would be how far in the relative future a trip would send you). This all of course requires exotic matter which probably doesn't exist; which is why this whole thing probably doesn't work in the first place (e.g. why stable wormholes probably don't exist). Still might make it's own excellent sci-fi book if someone ran with the constrains of this, and it would technically be harder sci-fi than most.