9 ms·

> Nothing you can do about latency, with speed of light and all that though Why do we take this for granted? I understand the laws of physics and all, but 120

> Nothing you can do about latency, with speed of light and all that though Why do we take this for granted? I understand the laws of physics and all, but 120 years ago we didn't think humans could fly through the air, and now we have a million+ humans flying every day, and occasionally one goes to outer space. Why do we consider communication faster than the speed of light so unbreakable?

fbanon 4y ago
120 years ago we knew that some things can fly, because we saw birds. We just had to figure out how to do the same with humans. On the other hand, we have never encountered anything in nature that goes faster than the speed of light. That's a pretty good hint that it's impossible to do so.
deleted 4y ago
[deleted]
tialaramex 4y ago
"The speed of light" is probably not what you think it is. This constant, c, is actually about how time (one of our four dimensions, often labelled t) is related to the three spatial dimensions (often x, y, z). Light goes that fast (in a vacuum) because from the light's point of view that's how those dimensions are related, it's not really a "speed limit" it's up against, any more than you'd consider it a "time limit" that hours have sixty minutes in them. The light is just moving through time as well as space, and that's how it has to work. So, because it's about the relationship between time and space, what you're talking about with "faster than light" is actually a time machine. Now, you might notice that before the aeroplane there were birds (and bats, and insects, but lets focus on birds). Clearly flying is possible, a sparrow can do it. But you may have noticed from the lack of time travelling visitors that time travel does not seem to be possible.
- jedberg 4y ago
  I knew that about the speed of light (but thank you for writing it out). My knowledge of entanglement is limited, but haven't we observed entangled particles seemingly communicate faster than light? While time travel may not be possible, maybe time traveling data is?
  - dsr_ 4y ago
    No, we have not. We have observed that we can generate a pair of particles and separate them, and when we look at the close one, we now know that the far one has the complementary property. You can't use that to send information. You could use it as a shared secret, but you still had to move the particle out where your recipient is for them to use it. You can take a flashlight and shine it at the moon, and if you sweep the beam back and forth, you can make the notional front of illumination move faster than the speed of light -- but you can't modulate the signal faster than the propagation velocity c. Time travel into the future is easy. Time travel into the past doesn't work in this universe.
  - ynik 4y ago
    Entanglement doesn't involve any form of communication. Only the imaginary "wave function collapse" is faster than light. But collapse isn't actually part of quantum mechanics: there's no formula that would tell you when collapse is triggered. The many world interpretation doesn't have any wave function collapse at all; and it's a valid interpretation of the underlying maths. Any "wave function collapse" is merely an interpretation trick to map the quantum world back to the classical world as experienced by humans. You can't build technology out of imaginary physics.
  - tambourine_man 4y ago
    Nope, it’s a common misunderstanding. While the particles are entangled regardless of distance and the action is instantaneous (at least, that’s one way of interpreting it) there’s no way to actually transmit information. You may try to come up with clever encodings for electron spins, but you’ll see that you end up having to know a priory what the other end had. It’s a long topic to discuss on a HN thread but a quick YouTube search will get you interesting videos.
  - nly 4y ago
    If time travel isn't possible how come we're all moving in to the future right now?
    - teddyh 4y ago
      “If flying is impossible for me after I have jumped off this tall building, how come I am currently moving through the air towards the ground at high speed?”
- didgetmaster 4y ago
  The lack of time travelling visitors may only indicate that 'backward' time travel is not possible. It could be that 'forward' time travel will be possible sometime in the future. (And by 'forward', I mean faster than the normal movement through time we all do every nanosecond)
  - gpderetta 4y ago
    That's relatively trivial by going at relativistic speed.
    - AnIrishDuck 4y ago
      This is even a thing at non-relativistic speeds. Proper operation of GPS requires a time correction [1] because the system's satellites are moving at significant speed from the perspective of ground observers. Their onboard clocks are therefore moving relatively faster through space, and thus relatively slower through time. This is measurable at the nanosecond scale, and must be taken into account every time something uses GPS. 1. https://www.astronomy.ohio-state.edu/pogge.1/Ast162/Unit5/gps.html https://www.astronomy.ohio-state.edu/pogge.1/Ast162/Unit5/gp...
      - tialaramex 4y ago
        I mean, technically what's going on is that satellites move at relativistic speed. "Relativistic speed" doesn't mean some particular speed, like 0.1c or something, it just means any speed where your measurements don't make sense without accounting for relativity, if your measurements were good enough this just doesn't have to be that fast really. However, do you remember simple school spring balance experiments which show Newtonian mechanics? Greg Egan's "Incandescence" is a novel about some people who live somewhere where those type of experiments need relativity to explain them, so, when they develop physics they go from "I dunno, it just always does that" straight to relativity because Newtonian mechanics don't explain what they already know about the world.
  - dagss 4y ago
    Entering and awakening from a coma comes pretty close...
deleted 4y ago
[deleted]
arccy 4y ago
We've been flying with hot air balloons for over 200 years, and we've seen birds (heavier than air) fly. It's always been considered possible, we just didn't know how to apply that to humans. We still haven't seen anything in nature that even hints to the possibility of faster than light
recursive 4y ago
Considering it breakable probably doesn't get you much. Ok, it's breakable. Now we just have no idea what to do. If anyone could demonstrate a proof of concept, I'm sure we'd be considering it much more broadly.
Jtsummers 4y ago
People had flown before the first powered flights, so 120 years isn't a good measure for that. You probably have to go back a lot further to find natural philosophers or physicists asserting that manned flight was totally impossible. Maybe claims that heavier than air vehicle couldn't fly would be more recent. Hot air balloons had been around since the 1700s, and gliders were developed in the 1800s. Those were the first "heavier than air" aircraft, and a manned glider was flown by the end of the 19th century. Powered flight was an extension of that model. We have no model of faster than light communication (or travel) that holds up to scrutiny, let alone has been demonstrated.
- gpderetta 4y ago
  Also birds.
mecsred 4y ago
Even if we could go back 120 years, just knowing it's possible to create aircraft doesn't do much without the domain knowledge to build one. FTL may or may not be possible via physics we don't understand. Until we have that physics and a system to exploit it FTL is a very real constraint to work around. Don't mistake "Nothing we can do" for "nothing we can ever do".
jvanderbot 4y ago
Never mind any down-votes, this is a reasonable question, and many here at HN would relish the opportunity to answer.
ynik 4y ago
Because of relativity. The speed of light is also the speed of causality. Assuming the theory of relativity isn't totally wrong, then if faster-than-light communication is possible, then so must be time travel. http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-ti...
- rightbyte 4y ago
  Why would information of an event, e.g. light bulb lit up by pushing breaker, decide the causality? Can't you just back track from a model that the breaker is closed then the bulb lits up?
  - moomin 4y ago
    The bulb lights up _after_ you close the breaker.
snowwrestler 4y ago
It’s not so much that we take it for granted, the issue is there is so far no contradicting evidence. Humans could see other animals flying, but we don’t see things going faster than the speed of light.
- t-3 4y ago
  > we don’t see things going faster than the speed of light. That would be physically impossible to see in the first place, wouldn't it?
  - pixl97 4y ago
    We would see some side effect of it depending on the exact nature of reality and time. Since we don't see things from the future randomly appearing now, nor do we have cherenkov radiation occurring in places that it shouldn't in open space it seems unlikely FTL is occurring.
shagie 4y ago
As an aside, the PBS space time video The Speed of Light is NOT About Light : https://youtu.be/msVuCEs8Ydo https://youtu.be/msVuCEs8Ydo As an aside to the aside - as I rewatch it I quickly notice how young he looks (and then note the date is 2015 on there - one of the early ones and the production is less refined). You may also like The Geometry of Causality https://youtu.be/1YFrISfN7jo https://youtu.be/1YFrISfN7jo
dboreham 4y ago
> Why do we consider communication faster than the speed of light so unbreakable? Because it's the definition of the simulator we inhabit. c isn't some random thing to do with light that we observe and find curious, it's literally the nature of the universe. The universe is "a place where the speed you can propagate information is : c". The speed of light follows from that, not the other way around. So if that's breakable, then we made some very big invalid assumptions over the past 200 years. Also, it's questionable that "we didn't think humans could fly through the air". Obviously some people did think that was possible, otherwise they wouldn't have tried to do so. We had birds and bats as existence proofs too. And balloons.
NateEag 4y ago
A combination of pragmatism and hubris. pragmatism: our best current theories about the universe suggest that the speed of light is a constant. Until someone proposes a theory with more explanatory power that suggests otherwise, we might as well do our work with the assumption that it's correct. Hubris: our best theories are clearly not complete (see dark matter, conflicts between general relativity and quantum mechanics, and similar), yet we mostly treat them not as provisional theories subject to change, but as ironclad laws by which we may live our lives. Humans don't do well with uncertainty. (Disclaimer: not everyone lives that way. As far as I can tell most who do have something like this combination of ideas in their heads.)
zasdffaa 4y ago
The only reason to post this is to troll.
- jedberg 4y ago
  Based on the downvotes I'm getting, it would appear a bunch of people agree with you, but I promise it is not. I genuinely want to understand why we consider this an unbreakable limit when we have in the past broken previously thought "unbreakable" limits.
  - zasdffaa 4y ago
    Ok I take your bona fides but why not just search? There are 186,283 sites covering this, so a quick <https://html.duckduckgo.com/html?q=why%20speed%20light%20limit https://html.duckduckgo.com/html?q=why%20speed%20light%20lim...> would have helped avoid irritating people, I mean you now have more info at your fingertips than any 10,000 people had collectively up until say 1980 and you don't even type a query?

fbanon 4y ago

120 years ago we knew that some things can fly, because we saw birds. We just had to figure out how to do the same with humans. On the other hand, we have never encountered anything in nature that goes faster than the speed of light. That's a pretty good hint that it's impossible to do so.

deleted 4y ago

[deleted]

tialaramex 4y ago

"The speed of light" is probably not what you think it is. This constant, c, is actually about how time (one of our four dimensions, often labelled t) is related to the three spatial dimensions (often x, y, z). Light goes that fast (in a vacuum) because from the light's point of view that's how those dimensions are related, it's not really a "speed limit" it's up against, any more than you'd consider it a "time limit" that hours have sixty minutes in them. The light is just moving through time as well as space, and that's how it has to work. So, because it's about the relationship between time and space, what you're talking about with "faster than light" is actually a time machine. Now, you might notice that before the aeroplane there were birds (and bats, and insects, but lets focus on birds). Clearly flying is possible, a sparrow can do it. But you may have noticed from the lack of time travelling visitors that time travel does not seem to be possible.

jedberg 4y ago
I knew that about the speed of light (but thank you for writing it out). My knowledge of entanglement is limited, but haven't we observed entangled particles seemingly communicate faster than light? While time travel may not be possible, maybe time traveling data is?
- dsr_ 4y ago
  No, we have not. We have observed that we can generate a pair of particles and separate them, and when we look at the close one, we now know that the far one has the complementary property. You can't use that to send information. You could use it as a shared secret, but you still had to move the particle out where your recipient is for them to use it. You can take a flashlight and shine it at the moon, and if you sweep the beam back and forth, you can make the notional front of illumination move faster than the speed of light -- but you can't modulate the signal faster than the propagation velocity c. Time travel into the future is easy. Time travel into the past doesn't work in this universe.
- ynik 4y ago
  Entanglement doesn't involve any form of communication. Only the imaginary "wave function collapse" is faster than light. But collapse isn't actually part of quantum mechanics: there's no formula that would tell you when collapse is triggered. The many world interpretation doesn't have any wave function collapse at all; and it's a valid interpretation of the underlying maths. Any "wave function collapse" is merely an interpretation trick to map the quantum world back to the classical world as experienced by humans. You can't build technology out of imaginary physics.
- tambourine_man 4y ago
  Nope, it’s a common misunderstanding. While the particles are entangled regardless of distance and the action is instantaneous (at least, that’s one way of interpreting it) there’s no way to actually transmit information. You may try to come up with clever encodings for electron spins, but you’ll see that you end up having to know a priory what the other end had. It’s a long topic to discuss on a HN thread but a quick YouTube search will get you interesting videos.
- nly 4y ago
  If time travel isn't possible how come we're all moving in to the future right now?
  - teddyh 4y ago
    “If flying is impossible for me after I have jumped off this tall building, how come I am currently moving through the air towards the ground at high speed?”
didgetmaster 4y ago
The lack of time travelling visitors may only indicate that 'backward' time travel is not possible. It could be that 'forward' time travel will be possible sometime in the future. (And by 'forward', I mean faster than the normal movement through time we all do every nanosecond)
- gpderetta 4y ago
  That's relatively trivial by going at relativistic speed.
  - AnIrishDuck 4y ago
    This is even a thing at non-relativistic speeds. Proper operation of GPS requires a time correction [1] because the system's satellites are moving at significant speed from the perspective of ground observers. Their onboard clocks are therefore moving relatively faster through space, and thus relatively slower through time. This is measurable at the nanosecond scale, and must be taken into account every time something uses GPS. 1. https://www.astronomy.ohio-state.edu/pogge.1/Ast162/Unit5/gps.html https://www.astronomy.ohio-state.edu/pogge.1/Ast162/Unit5/gp...
    - tialaramex 4y ago
      I mean, technically what's going on is that satellites move at relativistic speed. "Relativistic speed" doesn't mean some particular speed, like 0.1c or something, it just means any speed where your measurements don't make sense without accounting for relativity, if your measurements were good enough this just doesn't have to be that fast really. However, do you remember simple school spring balance experiments which show Newtonian mechanics? Greg Egan's "Incandescence" is a novel about some people who live somewhere where those type of experiments need relativity to explain them, so, when they develop physics they go from "I dunno, it just always does that" straight to relativity because Newtonian mechanics don't explain what they already know about the world.
- dagss 4y ago
  Entering and awakening from a coma comes pretty close...

deleted 4y ago

[deleted]

arccy 4y ago

We've been flying with hot air balloons for over 200 years, and we've seen birds (heavier than air) fly. It's always been considered possible, we just didn't know how to apply that to humans. We still haven't seen anything in nature that even hints to the possibility of faster than light

recursive 4y ago

Considering it breakable probably doesn't get you much. Ok, it's breakable. Now we just have no idea what to do. If anyone could demonstrate a proof of concept, I'm sure we'd be considering it much more broadly.

Jtsummers 4y ago

People had flown before the first powered flights, so 120 years isn't a good measure for that. You probably have to go back a lot further to find natural philosophers or physicists asserting that manned flight was totally impossible. Maybe claims that heavier than air vehicle couldn't fly would be more recent. Hot air balloons had been around since the 1700s, and gliders were developed in the 1800s. Those were the first "heavier than air" aircraft, and a manned glider was flown by the end of the 19th century. Powered flight was an extension of that model. We have no model of faster than light communication (or travel) that holds up to scrutiny, let alone has been demonstrated.

gpderetta 4y ago
Also birds.

mecsred 4y ago

Even if we could go back 120 years, just knowing it's possible to create aircraft doesn't do much without the domain knowledge to build one. FTL may or may not be possible via physics we don't understand. Until we have that physics and a system to exploit it FTL is a very real constraint to work around. Don't mistake "Nothing we can do" for "nothing we can ever do".

jvanderbot 4y ago

Never mind any down-votes, this is a reasonable question, and many here at HN would relish the opportunity to answer.

ynik 4y ago

Because of relativity. The speed of light is also the speed of causality. Assuming the theory of relativity isn't totally wrong, then if faster-than-light communication is possible, then so must be time travel. http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-ti...

rightbyte 4y ago
Why would information of an event, e.g. light bulb lit up by pushing breaker, decide the causality? Can't you just back track from a model that the breaker is closed then the bulb lits up?
- moomin 4y ago
  The bulb lights up _after_ you close the breaker.

snowwrestler 4y ago

It’s not so much that we take it for granted, the issue is there is so far no contradicting evidence. Humans could see other animals flying, but we don’t see things going faster than the speed of light.

t-3 4y ago
> we don’t see things going faster than the speed of light. That would be physically impossible to see in the first place, wouldn't it?
- pixl97 4y ago
  We would see some side effect of it depending on the exact nature of reality and time. Since we don't see things from the future randomly appearing now, nor do we have cherenkov radiation occurring in places that it shouldn't in open space it seems unlikely FTL is occurring.

shagie 4y ago

As an aside, the PBS space time video The Speed of Light is NOT About Light : https://youtu.be/msVuCEs8Ydo https://youtu.be/msVuCEs8Ydo As an aside to the aside - as I rewatch it I quickly notice how young he looks (and then note the date is 2015 on there - one of the early ones and the production is less refined). You may also like The Geometry of Causality https://youtu.be/1YFrISfN7jo https://youtu.be/1YFrISfN7jo

dboreham 4y ago

> Why do we consider communication faster than the speed of light so unbreakable? Because it's the definition of the simulator we inhabit. c isn't some random thing to do with light that we observe and find curious, it's literally the nature of the universe. The universe is "a place where the speed you can propagate information is : c". The speed of light follows from that, not the other way around. So if that's breakable, then we made some very big invalid assumptions over the past 200 years. Also, it's questionable that "we didn't think humans could fly through the air". Obviously some people did think that was possible, otherwise they wouldn't have tried to do so. We had birds and bats as existence proofs too. And balloons.

NateEag 4y ago

A combination of pragmatism and hubris. pragmatism: our best current theories about the universe suggest that the speed of light is a constant. Until someone proposes a theory with more explanatory power that suggests otherwise, we might as well do our work with the assumption that it's correct. Hubris: our best theories are clearly not complete (see dark matter, conflicts between general relativity and quantum mechanics, and similar), yet we mostly treat them not as provisional theories subject to change, but as ironclad laws by which we may live our lives. Humans don't do well with uncertainty. (Disclaimer: not everyone lives that way. As far as I can tell most who do have something like this combination of ideas in their heads.)

zasdffaa 4y ago

The only reason to post this is to troll.

jedberg 4y ago
Based on the downvotes I'm getting, it would appear a bunch of people agree with you, but I promise it is not. I genuinely want to understand why we consider this an unbreakable limit when we have in the past broken previously thought "unbreakable" limits.
- zasdffaa 4y ago
  Ok I take your bona fides but why not just search? There are 186,283 sites covering this, so a quick <https://html.duckduckgo.com/html?q=why%20speed%20light%20limit https://html.duckduckgo.com/html?q=why%20speed%20light%20lim...> would have helped avoid irritating people, I mean you now have more info at your fingertips than any 10,000 people had collectively up until say 1980 and you don't even type a query?