6 ms·

In that vein, Newton and Kelvin both "proved" that heavier-than-air flying machines were physically impossible. That belief held for hundreds of years, and like

In that vein, Newton and Kelvin both "proved" that heavier-than-air flying machines were physically impossible. That belief held for hundreds of years, and likely put many off even trying. Einstein said that nuclear fission was impossible, before Fermi promptly proved him dead wrong. I'm not saying that we're wrong about c, but we don't know what we don't know.

dalke 10y ago
Which is why Stross ended with: > Anyway, the point I'd like you to take away from this is that while it's really hard to say "sending an interstellar probe is absolutely impossible", the smart money says that it's extremely difficult to do it using any technology currently existing or in development. We'd need a whole raft of breathroughs, including radiation shielding techniques to kick the interstellar medium out of the way of the probe as well as some sort of beam propulsion system and then some way of getting data back home across interstellar distances ... You wrote: "Einstein said that nuclear fission was impossible". Do you have a reference for that? The closest account I know is described at http://www.doug-long.com/einstein.htm http://www.doug-long.com/einstein.htm : > Among those concerned were physicists Leo Szilard and Eugene Wigner. But Szilard and Wigner had no influence with those in power. So in July 1939 they explained the problem to someone who did: Albert Einstein. According to Szilard, Einstein said the possibility of a chain reaction "never occurred to me", altho Einstein was quick to understand the concept (Clark, pg. 669+; Spencer Weart & Gertrud Weiss Szilard, eds., "Leo Szilard: His Version of the Facts", pg. 83). but that wasn't about nuclear fission per se but of a chain reaction. Also, how was Fermi involved? Fission was "was discovered on December 17, 1938 by German Otto Hahn and his assistant Fritz Strassmann, and explained theoretically in January 1939 by Lise Meitner and her nephew Otto Robert Frisch." - https://en.wikipedia.org/wiki/Nuclear_fission https://en.wikipedia.org/wiki/Nuclear_fission .
- rjsw 10y ago
  Fermi supervised the first demonstration of fission [1]. [1] https://en.wikipedia.org/wiki/Chicago_Pile-1 https://en.wikipedia.org/wiki/Chicago_Pile-1
  - dalke 10y ago
    Yes. But as that link point out, it was years after (and a consequence of) the Einstein–Szilard letter. When did Einstein say nuclear fission was impossible, and how was it Fermi who "promptly proved him dead wrong", as madaxe_again wrote? Edit: jsnathan at https://news.ycombinator.com/item?id=12326618 https://news.ycombinator.com/item?id=12326618 found a 1934 quote by Einstein expressing an opinion that nuclear power wasn't possible. This is after fission was already demonstrated.
    - kryptiskt 10y ago
      Fission was discovered in 1938. Fermi observed fission but drew the wrong conclusions, he thought he saw creation of transuranic elements.
avian 10y ago
> Newton and Kelvin both "proved" that heavier-than-air flying machines were physically impossible. Can we please stop bringing this up? Same with the "faster than sound flight is impossible" quote. Kelvin was well aware that birds were heavier than air and before supersonic flight it was well known how fast a cannon ball can fly. These people were talking about engineering and economic realities of their time, not physical laws. In contrast, we currently know of no natural phenomena that would hint at the possibility of faster-than-light travel and in fact have good reasons to believe that it is impossible.
- b6 10y ago
  > we currently know of no natural phenomena that would hint at the possibility of faster-than-light travel and in fact have good reasons to believe that it is impossible Is this true? I thought that if my ship is capable, I can go as fast as I like. I just won't appear to be going faster than light to somebody else.
  - rfrey 10y ago
    You are being downvoted for your misunderstanding, which is too bad. In a nutshell, no matter how much energy you pump into your system, you will never go faster than the speed of light, relative to any other viewpoint. That is, you would never appear to go faster than the speed of light to anyone - including somebody travelling at the same speed as you in the opposite direction.
    - sp332 10y ago
      The universe outside your window won't be passing by faster than the speed of light either. But that's a bit moot, since Lorentz contraction will make the distances in your line of travel shorter. Also time will pass more slowly for you. So subjectively, it's true that you can get anywhere in an arbitrarily small amount of time if you have arbitrarily large amounts of energy, but the rest of the universe will still see you only approaching the speed of light.
    - panic 10y ago
jeffwass 10y ago
>Einstein said that nuclear fission was impossible, before Fermi promptly proved him dead wrong. Reference please. And was this before or after the famous Einstein-Szilard letter to Roosevelt, which not only motivated the Manhattan Project but also specifically referenced Fermi's unfinished theoretical research of a possible chain reaction in uranium?
- jsnathan 10y ago
  Google found me this [1]. "On 29 December 1934, Albert Einstein was quoted in the Pittsburgh Post-Gazette as saying, “There is not the slightest indication that [nuclear energy] will ever be obtainable. It would mean that the atom would have to be shattered at will.” This followed the discovery that year by Enrico Fermi that if you bombard uranium with neutrons, the uranium atoms split up into lighter elements, releasing energy." This would be before the 1939 letter. [1]: https://www.newscientist.com/article/dn13556-10-impossibilities-conquered-by-science/ https://www.newscientist.com/article/dn13556-10-impossibilit...
  - SideburnsOfDoom 10y ago
    Do not confuse "no indication that [nuclear energy] will ever be obtainable" (there is no evidence that it is an achievable engineering feat) with "it is impossible" (it is explicitly not permitted by physics as we understand it)
    - jsnathan 10y ago
      You're probably right about Einstein not suggesting there was a hard physical limit preventing nuclear energy. But I don't think that hard physical limits are a good argument anyway. There are FTL proposals that do not violate known physics, such as distorting spacetime using some perhaps yet unknown mechanism. Saying that there are hard limits in physics here, as you did, suggests that research in this direction is not worth our time. I believe that is misleading.
  - kryptiskt 10y ago
    That seems way bogus to me. Fermi and the physics world believed that he had found transuranic elements. It was Hahn, Meitner and Strassman who said it was fission in late 1938 (a couple of months after Fermi got the Nobel citing that discovery, but no worries, he had done plenty of Nobel-worthy things).

dalke 10y ago

Which is why Stross ended with: > Anyway, the point I'd like you to take away from this is that while it's really hard to say "sending an interstellar probe is absolutely impossible", the smart money says that it's extremely difficult to do it using any technology currently existing or in development. We'd need a whole raft of breathroughs, including radiation shielding techniques to kick the interstellar medium out of the way of the probe as well as some sort of beam propulsion system and then some way of getting data back home across interstellar distances ... You wrote: "Einstein said that nuclear fission was impossible". Do you have a reference for that? The closest account I know is described at http://www.doug-long.com/einstein.htm http://www.doug-long.com/einstein.htm : > Among those concerned were physicists Leo Szilard and Eugene Wigner. But Szilard and Wigner had no influence with those in power. So in July 1939 they explained the problem to someone who did: Albert Einstein. According to Szilard, Einstein said the possibility of a chain reaction "never occurred to me", altho Einstein was quick to understand the concept (Clark, pg. 669+; Spencer Weart & Gertrud Weiss Szilard, eds., "Leo Szilard: His Version of the Facts", pg. 83). but that wasn't about nuclear fission per se but of a chain reaction. Also, how was Fermi involved? Fission was "was discovered on December 17, 1938 by German Otto Hahn and his assistant Fritz Strassmann, and explained theoretically in January 1939 by Lise Meitner and her nephew Otto Robert Frisch." - https://en.wikipedia.org/wiki/Nuclear_fission https://en.wikipedia.org/wiki/Nuclear_fission .

rjsw 10y ago
Fermi supervised the first demonstration of fission [1]. [1] https://en.wikipedia.org/wiki/Chicago_Pile-1 https://en.wikipedia.org/wiki/Chicago_Pile-1
- dalke 10y ago
  Yes. But as that link point out, it was years after (and a consequence of) the Einstein–Szilard letter. When did Einstein say nuclear fission was impossible, and how was it Fermi who "promptly proved him dead wrong", as madaxe_again wrote? Edit: jsnathan at https://news.ycombinator.com/item?id=12326618 https://news.ycombinator.com/item?id=12326618 found a 1934 quote by Einstein expressing an opinion that nuclear power wasn't possible. This is after fission was already demonstrated.
  - kryptiskt 10y ago
    Fission was discovered in 1938. Fermi observed fission but drew the wrong conclusions, he thought he saw creation of transuranic elements.

avian 10y ago

> Newton and Kelvin both "proved" that heavier-than-air flying machines were physically impossible. Can we please stop bringing this up? Same with the "faster than sound flight is impossible" quote. Kelvin was well aware that birds were heavier than air and before supersonic flight it was well known how fast a cannon ball can fly. These people were talking about engineering and economic realities of their time, not physical laws. In contrast, we currently know of no natural phenomena that would hint at the possibility of faster-than-light travel and in fact have good reasons to believe that it is impossible.

b6 10y ago
> we currently know of no natural phenomena that would hint at the possibility of faster-than-light travel and in fact have good reasons to believe that it is impossible Is this true? I thought that if my ship is capable, I can go as fast as I like. I just won't appear to be going faster than light to somebody else.
- rfrey 10y ago
  You are being downvoted for your misunderstanding, which is too bad. In a nutshell, no matter how much energy you pump into your system, you will never go faster than the speed of light, relative to any other viewpoint. That is, you would never appear to go faster than the speed of light to anyone - including somebody travelling at the same speed as you in the opposite direction.
  - sp332 10y ago
    The universe outside your window won't be passing by faster than the speed of light either. But that's a bit moot, since Lorentz contraction will make the distances in your line of travel shorter. Also time will pass more slowly for you. So subjectively, it's true that you can get anywhere in an arbitrarily small amount of time if you have arbitrarily large amounts of energy, but the rest of the universe will still see you only approaching the speed of light.
  - panic 10y ago

jeffwass 10y ago

>Einstein said that nuclear fission was impossible, before Fermi promptly proved him dead wrong. Reference please. And was this before or after the famous Einstein-Szilard letter to Roosevelt, which not only motivated the Manhattan Project but also specifically referenced Fermi's unfinished theoretical research of a possible chain reaction in uranium?

jsnathan 10y ago
Google found me this [1]. "On 29 December 1934, Albert Einstein was quoted in the Pittsburgh Post-Gazette as saying, “There is not the slightest indication that [nuclear energy] will ever be obtainable. It would mean that the atom would have to be shattered at will.” This followed the discovery that year by Enrico Fermi that if you bombard uranium with neutrons, the uranium atoms split up into lighter elements, releasing energy." This would be before the 1939 letter. [1]: https://www.newscientist.com/article/dn13556-10-impossibilities-conquered-by-science/ https://www.newscientist.com/article/dn13556-10-impossibilit...
- SideburnsOfDoom 10y ago
  Do not confuse "no indication that [nuclear energy] will ever be obtainable" (there is no evidence that it is an achievable engineering feat) with "it is impossible" (it is explicitly not permitted by physics as we understand it)
  - jsnathan 10y ago
    You're probably right about Einstein not suggesting there was a hard physical limit preventing nuclear energy. But I don't think that hard physical limits are a good argument anyway. There are FTL proposals that do not violate known physics, such as distorting spacetime using some perhaps yet unknown mechanism. Saying that there are hard limits in physics here, as you did, suggests that research in this direction is not worth our time. I believe that is misleading.
- kryptiskt 10y ago
  That seems way bogus to me. Fermi and the physics world believed that he had found transuranic elements. It was Hahn, Meitner and Strassman who said it was fission in late 1938 (a couple of months after Fermi got the Nobel citing that discovery, but no worries, he had done plenty of Nobel-worthy things).