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This is like saying we will never fly a plane. Do you really think people in the 1200's could fathom a phone or the internet or access all information that ever

This is like saying we will never fly a plane. Do you really think people in the 1200's could fathom a phone or the internet or access all information that ever has been on a device that fits on your phone? Its incredibly naïve to think that time travel isn't possible purely based on "laws of physics".

roywiggins 5y ago
There's prior art for flight. There's no prior art for time travel.
hn_throwaway_99 5y ago
> Its incredibly naïve to think that time travel isn't possible purely based on "laws of physics". Huh? Would you argue that it's "incredibly naïve" to think perpetual motion machines aren't possible purely based on "laws of physics"? Because I think it's incredibly naïve to think perpetual motion machines would be possible, precisely because they do violate the laws of physics.
- patrick0d 5y ago
  Eddington said: "The law that entropy always increases—the Second Law of Thermodynamics—holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell’s equations—then so much the worse for Maxwell’s equations. If it is found to be contradicted by observation—well these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation." But hey there's a lot we still don't know about the universe. I mean these unbreakable laws are only a few hundred years old for us.
- tjs8rj 5y ago
  The most we can really conclude is that they don't currently appear to be possible. We have a sample size of 1 with how many universes we've studied. As far we know, this could be a simulation, or a brief moment in time when the ever-shifting laws of physics look the way they do, or the dream of a supernatural being. By all means, our physics works (now) and its the best we've got so lets bet on it and drive our society that way, but to suggest some things will never be possible not only creates 0 value for society (perhaps even negative value), but is also the stance proven wrong so many times needlessly. The truth is, we really just don't know and can only make our best guesses.
  - lazide 5y ago
    Except that when people try to use fantastical stories of perpetual motion machines to bilk investors or the like, not calling bullshit does have a net negative. There is ‘plausible imagining’ and then there is also ‘scammy bullshit’.
- cjg 5y ago
  We can already see how the laws of physics might accommodate energy not being conserved - and from there a small hop to perpetual motion machines. Energy conservation relies on time translation symmetry. In other words, that the laws of physics do not change over time. Well, perhaps they do change slowly. A prime example of this is the expansion of spacetime, which can reduce the energy of a photon travelling through empty space - it's redshifted. This has been experimentally observed. See https://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/ https://www.preposterousuniverse.com/blog/2010/02/22/energy-... for more details.
  - Koshkin 5y ago
    Isn't redshift a results of the change in the observable wavelength, i.e. the photon's momentum?
    - LegitShady 5y ago
      The energy of a photon is defined as E = (hc)/λ where h is the planck constant, c is the speed of light, and λ is the wavelength. As a redshift is the increase in wavelength it is an actual decrease in the energy of the photon. This makes more sense when you consider that a photon is mass-less, and so its total, energy is bound up in its momentum rather than momentum and mass.
- new_guy 5y ago
  > Because I think it's incredibly naïve to think perpetual motion machines would be possible, precisely because they do violate the laws of physics. What do people mean by 'perpetual'? 1 year, 100 years, 1 million, is it expected to outlast the universe? And 'laws of physics' is such an anachronistic term, it carries such baggage with it, better to say 'what we think we know so far'. And a 'perpetual energy machine' is trivial, punch a hole through to another universe and siphon their energy out. That's probably what black holes are, another universe has punched a hole through to ours and is sucking the energy out. Is it perpetual? Well, it'll last a billion years or so. Does it violate our naive understanding of physics? Not at all.
  - hn_throwaway_99 5y ago
    > And a 'perpetual energy machine' is trivial, punch a hole through to another universe and siphon their energy out. That's probably what black holes are, another universe has punched a hole through to ours and is sucking the energy out. I also sometimes smoke too much weed.
  - lazide 5y ago
    If someone was selling a perpetual motion machine for $1 million dollars, would you be a genius or a rube to buy it?
tjs8rj 5y ago
"The universe is not only queerer than we suppose, but queerer than we can suppose" - J. B. S. Haldane I've seen so many documentaries and articles pessimistically concluding we'll never go to another star much less another galaxy based on the speed of light. Once again, too many smart people conclude we've figured it all out as is the perennial tradition.
- _carbyau_ 5y ago
  Scientists work on the basis of "what we know" because from a practical point, you can't work off a foundation of what you don't know. When pushed, all scientists will admit "based on current understanding". This is what makes a "breakthrough" revision of understanding so exciting! It doesn't happen every day!
spaetzleesser 5y ago
I am always trying to imagine what kinds of stuff will be possible in 10000 years if science keeps progressing. At the present we have things that people a few hundred years ago couldn’t even have imagined. I guess it’s impossible to imagine what people will have in the future but I would really like to know.
deleted 5y ago
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katmannthree 5y ago
Think of the statement as “backwards time travel existing would break our model of causality which has so far held up to observation.” It’s essentially Occam’s razor. Of course we could currently be wrong, but the entire point of the western scientific mindset in which this article is written is that we can be reasonably certain that in this case we’re not. If you want to dedicate your efforts to showing otherwise, have at it. No one will stop you. They probably won’t fund you though, and on the minuscule chance you end up being right unless it’s blindingly obvious it’ll take a while to convince people (we still haven’t convinced everyone that the standard model matches experimental data as well as it does, and that’s more or less been settled for how many decades now?)
felix318 5y ago
It’s not just the laws of physics. If you assume the past cannot be changed then you can’t physically interact with it, and you can’t even observe it (observation is interaction). And if you assume the past can be changed then the universe makes no sense and all discussion is futile.
- Beldin 5y ago
  We observe the past all the time. It's most noticeable in astronomy, but since the speed of light is finite, it's impossible to observe the present. Ever. Any observation is based on light (or something slower) travelling to you. The universe may not make a lot of sense, but there is some sense in it. Futility of discussion: I can certainly understand anyone feeling like that after the last two years. But don't give up hope!
Koshkin 5y ago
It is incredibly naïve to think that a thought based on knowledge has the same value as a thought based on ignorance.
- trevyn 5y ago
  Knowledge of one’s ignorance is also valuable. Specifically, saying that something is “impossible” outside of a well-defined formal system would more correctly be classed as hyperbole than a statement based on knowledge.
nonameiguess 5y ago
The laws of physics as we know them today don't forbid time travel. In fact, they propose a fairly specific means of doing it via accelerating one side of a traversable wormhole to near the speed of light. The only reason this isn't actionable is it requires exotic matter that may not exist, and if it does, we certainly don't know where to find it or how to make it (and we don't currently know how to make a wormhole, but we know they're physically possible). Usually, when people rule out time travel as impossible, it's because it has the potential to introduce paradoxes that totally break any possible understandable notion of causality, i.e. the inventor of time travel going back and killing himself before he invents it. Thankfully, the known physically possible forms of time travel don't introduce that specific issue as they would not permit traveling back to any point before the wormhole was created, which also goes far to explaining why, if time travel is ever going to be invented in the future, we have never seen anyone come here from the future.
- short_sells_poo 5y ago
  > and we don't currently know how to make a wormhole, but we know they're physically possible I'm not aware of any actual observational evidence or even strong theoretical prediction that wormholes exist or that they are physically possible. Some parameterizations of our models don't rule out their existence, but it's all hypothetical. Including the question whether they are traversable.
- nobody9999 5y ago
  >The laws of physics as we know them today don't forbid time travel. In fact, they propose a fairly specific means of doing it via accelerating one side of a traversable wormhole to near the speed of light. That applies to time travel into the past. It's obvious, but it bears noting that the converse is a lot simpler. I say that because, IIUC (and that's a real question), quantum mechanics treats the time dimension as symmetrical, which contradicts observation, at least to this point. Is that because QM is wrong on that point? Which seems unlikely, since it's one of the most precisely confirmed (by observation) theories we have. Or is there something about the "macro" world that destroys that symmetry? I don't have the answer, but it's clear that in a particular reference frame, we move forward in time at a rate of 1 sec/second. Again, that's obvious, but based on my (limited) understanding, that seems to contradict QM.
paulmooreparks 5y ago
This is nothing like saying we will never fly a plane. Flight was always quite obviously possible, physically. Birds and other flying creatures did it all the time. Gliders existed long before powered flight, so the basics of aerodynamics were understood well ahead of powered flight. Understanding time travel and its possibility is definitely purely based on the laws of physics. What else would it be based on?
analog31 5y ago
Why do you you think that people in the 1200s will never be able to use the Internet? Likewise, why do you think that flying a plane will remain possible in the future or that we will have had computers in the past? Those things are all based on assuming "laws of physics."
breuleux 5y ago
> Do you really think people in the 1200's could fathom a phone or the internet or access all information that ever has been on a device that fits on your phone? Yes? People in the 1200s could fathom gods and magic, why not phones? What kind of dullards do you think people were back then? The futures people imagine are consistently crazier than what actually happens. People thought that by year 2000 we'd have Mars colonies, flying cars and sentient computers. Sure, they didn't really see the Internet coming, and sure, the Internet is nice, but it's not exactly up to par, is it?
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roywiggins 5y ago

There's prior art for flight. There's no prior art for time travel.

hn_throwaway_99 5y ago

> Its incredibly naïve to think that time travel isn't possible purely based on "laws of physics". Huh? Would you argue that it's "incredibly naïve" to think perpetual motion machines aren't possible purely based on "laws of physics"? Because I think it's incredibly naïve to think perpetual motion machines would be possible, precisely because they do violate the laws of physics.

patrick0d 5y ago
Eddington said: "The law that entropy always increases—the Second Law of Thermodynamics—holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell’s equations—then so much the worse for Maxwell’s equations. If it is found to be contradicted by observation—well these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation." But hey there's a lot we still don't know about the universe. I mean these unbreakable laws are only a few hundred years old for us.
tjs8rj 5y ago
The most we can really conclude is that they don't currently appear to be possible. We have a sample size of 1 with how many universes we've studied. As far we know, this could be a simulation, or a brief moment in time when the ever-shifting laws of physics look the way they do, or the dream of a supernatural being. By all means, our physics works (now) and its the best we've got so lets bet on it and drive our society that way, but to suggest some things will never be possible not only creates 0 value for society (perhaps even negative value), but is also the stance proven wrong so many times needlessly. The truth is, we really just don't know and can only make our best guesses.
- lazide 5y ago
  Except that when people try to use fantastical stories of perpetual motion machines to bilk investors or the like, not calling bullshit does have a net negative. There is ‘plausible imagining’ and then there is also ‘scammy bullshit’.
cjg 5y ago
We can already see how the laws of physics might accommodate energy not being conserved - and from there a small hop to perpetual motion machines. Energy conservation relies on time translation symmetry. In other words, that the laws of physics do not change over time. Well, perhaps they do change slowly. A prime example of this is the expansion of spacetime, which can reduce the energy of a photon travelling through empty space - it's redshifted. This has been experimentally observed. See https://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/ https://www.preposterousuniverse.com/blog/2010/02/22/energy-... for more details.
- Koshkin 5y ago
  Isn't redshift a results of the change in the observable wavelength, i.e. the photon's momentum?
  - LegitShady 5y ago
    The energy of a photon is defined as E = (hc)/λ where h is the planck constant, c is the speed of light, and λ is the wavelength. As a redshift is the increase in wavelength it is an actual decrease in the energy of the photon. This makes more sense when you consider that a photon is mass-less, and so its total, energy is bound up in its momentum rather than momentum and mass.
new_guy 5y ago
> Because I think it's incredibly naïve to think perpetual motion machines would be possible, precisely because they do violate the laws of physics. What do people mean by 'perpetual'? 1 year, 100 years, 1 million, is it expected to outlast the universe? And 'laws of physics' is such an anachronistic term, it carries such baggage with it, better to say 'what we think we know so far'. And a 'perpetual energy machine' is trivial, punch a hole through to another universe and siphon their energy out. That's probably what black holes are, another universe has punched a hole through to ours and is sucking the energy out. Is it perpetual? Well, it'll last a billion years or so. Does it violate our naive understanding of physics? Not at all.
- hn_throwaway_99 5y ago
  > And a 'perpetual energy machine' is trivial, punch a hole through to another universe and siphon their energy out. That's probably what black holes are, another universe has punched a hole through to ours and is sucking the energy out. I also sometimes smoke too much weed.
- lazide 5y ago
  If someone was selling a perpetual motion machine for $1 million dollars, would you be a genius or a rube to buy it?

tjs8rj 5y ago

"The universe is not only queerer than we suppose, but queerer than we can suppose" - J. B. S. Haldane I've seen so many documentaries and articles pessimistically concluding we'll never go to another star much less another galaxy based on the speed of light. Once again, too many smart people conclude we've figured it all out as is the perennial tradition.

_carbyau_ 5y ago
Scientists work on the basis of "what we know" because from a practical point, you can't work off a foundation of what you don't know. When pushed, all scientists will admit "based on current understanding". This is what makes a "breakthrough" revision of understanding so exciting! It doesn't happen every day!

spaetzleesser 5y ago

I am always trying to imagine what kinds of stuff will be possible in 10000 years if science keeps progressing. At the present we have things that people a few hundred years ago couldn’t even have imagined. I guess it’s impossible to imagine what people will have in the future but I would really like to know.

deleted 5y ago

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katmannthree 5y ago

Think of the statement as “backwards time travel existing would break our model of causality which has so far held up to observation.” It’s essentially Occam’s razor. Of course we could currently be wrong, but the entire point of the western scientific mindset in which this article is written is that we can be reasonably certain that in this case we’re not. If you want to dedicate your efforts to showing otherwise, have at it. No one will stop you. They probably won’t fund you though, and on the minuscule chance you end up being right unless it’s blindingly obvious it’ll take a while to convince people (we still haven’t convinced everyone that the standard model matches experimental data as well as it does, and that’s more or less been settled for how many decades now?)

felix318 5y ago

It’s not just the laws of physics. If you assume the past cannot be changed then you can’t physically interact with it, and you can’t even observe it (observation is interaction). And if you assume the past can be changed then the universe makes no sense and all discussion is futile.

Beldin 5y ago
We observe the past all the time. It's most noticeable in astronomy, but since the speed of light is finite, it's impossible to observe the present. Ever. Any observation is based on light (or something slower) travelling to you. The universe may not make a lot of sense, but there is some sense in it. Futility of discussion: I can certainly understand anyone feeling like that after the last two years. But don't give up hope!

Koshkin 5y ago

It is incredibly naïve to think that a thought based on knowledge has the same value as a thought based on ignorance.

trevyn 5y ago
Knowledge of one’s ignorance is also valuable. Specifically, saying that something is “impossible” outside of a well-defined formal system would more correctly be classed as hyperbole than a statement based on knowledge.

nonameiguess 5y ago

The laws of physics as we know them today don't forbid time travel. In fact, they propose a fairly specific means of doing it via accelerating one side of a traversable wormhole to near the speed of light. The only reason this isn't actionable is it requires exotic matter that may not exist, and if it does, we certainly don't know where to find it or how to make it (and we don't currently know how to make a wormhole, but we know they're physically possible). Usually, when people rule out time travel as impossible, it's because it has the potential to introduce paradoxes that totally break any possible understandable notion of causality, i.e. the inventor of time travel going back and killing himself before he invents it. Thankfully, the known physically possible forms of time travel don't introduce that specific issue as they would not permit traveling back to any point before the wormhole was created, which also goes far to explaining why, if time travel is ever going to be invented in the future, we have never seen anyone come here from the future.

short_sells_poo 5y ago
> and we don't currently know how to make a wormhole, but we know they're physically possible I'm not aware of any actual observational evidence or even strong theoretical prediction that wormholes exist or that they are physically possible. Some parameterizations of our models don't rule out their existence, but it's all hypothetical. Including the question whether they are traversable.
nobody9999 5y ago
>The laws of physics as we know them today don't forbid time travel. In fact, they propose a fairly specific means of doing it via accelerating one side of a traversable wormhole to near the speed of light. That applies to time travel into the past. It's obvious, but it bears noting that the converse is a lot simpler. I say that because, IIUC (and that's a real question), quantum mechanics treats the time dimension as symmetrical, which contradicts observation, at least to this point. Is that because QM is wrong on that point? Which seems unlikely, since it's one of the most precisely confirmed (by observation) theories we have. Or is there something about the "macro" world that destroys that symmetry? I don't have the answer, but it's clear that in a particular reference frame, we move forward in time at a rate of 1 sec/second. Again, that's obvious, but based on my (limited) understanding, that seems to contradict QM.

paulmooreparks 5y ago

This is nothing like saying we will never fly a plane. Flight was always quite obviously possible, physically. Birds and other flying creatures did it all the time. Gliders existed long before powered flight, so the basics of aerodynamics were understood well ahead of powered flight. Understanding time travel and its possibility is definitely purely based on the laws of physics. What else would it be based on?

analog31 5y ago

Why do you you think that people in the 1200s will never be able to use the Internet? Likewise, why do you think that flying a plane will remain possible in the future or that we will have had computers in the past? Those things are all based on assuming "laws of physics."

breuleux 5y ago

> Do you really think people in the 1200's could fathom a phone or the internet or access all information that ever has been on a device that fits on your phone? Yes? People in the 1200s could fathom gods and magic, why not phones? What kind of dullards do you think people were back then? The futures people imagine are consistently crazier than what actually happens. People thought that by year 2000 we'd have Mars colonies, flying cars and sentient computers. Sure, they didn't really see the Internet coming, and sure, the Internet is nice, but it's not exactly up to par, is it?

deleted 5y ago

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