11 ms·

Waiting for the physicist in the room to point out: there is no such thing as simultaneity! :)

by gfiorav 6y ago

theNJR 6y ago
Came here to suggest The Order of Time by C Rovelli, which explains this in such a captivating way.
- amelius 6y ago
  I think this video explains the issue quite well in only two minutes: https://www.youtube.com/watch?v=wteiuxyqtoM https://www.youtube.com/watch?v=wteiuxyqtoM
  - melenaboija 6y ago
    Another one here, it is in Catalan but with subtitles in english. Minute 18 is where it is explained although I think is worth it to watch all of it https://www.ccma.cat/tv3/alacarta/quequicom/tempus-fugit-subtitulat-en-angles/video/5540737/ https://www.ccma.cat/tv3/alacarta/quequicom/tempus-fugit-sub...
  - Dylan16807 6y ago
    But that only happens with sufficiently high relative velocities. Earth and Mars are effectively in the same reference frame.
deleted 6y ago
[deleted]
Daho0n 6y ago
S/he already did. We just don't know yet.
- extropy 6y ago
  She both did and did not until we observe :p. And even that is not correct. Events happening propagate with speed of light - the event horizon. We can predict we will receive information of something happening, bit that's just prediction about future events, regardless of the location.
- fckthisguy 6y ago
  You can just say "they". (Not trying to be judgy. People just seem to forget about the gender neutral use of "they".)
  - buzzerbetrayed 6y ago
    There are like 500 other ways you could have said what you just said as well. Doesn’t mean the way you said it is invalid.
  - unanswered 6y ago
    Why is it acceptable to use the wrong pronoun, such as "they", for someone who chooses the pronoun "she" or "he"?
    - randomchars 6y ago
      > used to refer to a person of unspecified gender. How is this offensive to anyone??
      - unanswered 6y ago
        For the same reason referring to anyone with the wrong pronouns is, I would assume. Isn't that offensive? I didn't realize this was up for debate in 2021.
        randomchars 6y ago
        But you're not referring to someone with the wrong pronoun, but using a gender neutral one.
        unanswered 6y ago
        I'm sorry, I honestly don't understand what distinction you're trying to point out. If someone's preferred pronoun is "she", for example, and I refer to her as a "they", then that's the wrong pronoun, isn't it? That's literally the definition of "wrong", at least the definition I understand. The right pronoun is "she" and other pronouns such as "he" and "they" and "it" are, by exclusion, wrong. But it seems like you're saying there's some kind of complex relation where sometimes people don't get to choose their own pronouns, but other people get to choose which one out of many to use based on convenience. Maybe it would help my understand if you could provide a chart relating the pronouns someone chooses with the pronouns other people are then allowed to use?
whatshisface 6y ago
Simultaneity is at least as well defined as clock time. Both clock time and the velocity of your reference frame can have arbitrary constants added to them to yield equally valid coordinate systems. So "it's not really simultaneous" is analogous to "it's not really 6:30 PM."
- bregma 6y ago
  Well, it's 6:30 PM somewhere. lifts glass
  - UnpossibleJim 6y ago
    From The Hitchhiker's Guide to the Galaxy: "Time is an illusion. Lunchtime doubly so."
walrus01 6y ago
> simultaneity not in the true accurate to the picosecond sense of the word, no, but the exact word simultaneity is used when discussing number and density of satellites about a given latitude/longitude in the starlink beta program. Since they're LEO and orbiting at only 550 km, the satellites above a given spot on the ground vary greatly in the not-yet-complete sparse network. Usually related to discussions of whether a beta test customer terminal will briefly hiccup and lose connection to its default gateway, or if somebody is at a sufficiently high latitude that they can have full coverage for all 86400 seconds in a day. https://satellitemap.space/ https://satellitemap.space/ has a good animated visualization of this.
cphajduk 6y ago
Depends what type of physicist you ask. According to the energy-time uncertainty principle we don't even know when exactly the RF waves that transmitted information hit the receiver on Earth either.
cambalache 6y ago
Oh but there is. Just not in the same frame of reference.
avz 6y ago
In the absence of a physicist, I suppose that a software engineer in the room might do. After all, the counterintuitive consequences of relativity have their counterparts in counterintuitive effects in distributed systems and concurrent programming. In both cases, the core issue that misleads our intuition is the lack of a shared global clock that would impose a total ordering [1] on events/reads/writes/etc. Instead, events in both situations are only ordered partially [2]. In relativity the ordering is determined by the speed of light, in distributed systems the ordering is determined by what messages have been exchanged by two nodes and in concurrent programming reads and writes are ordered by synchronization actions such as lock acquisition and release, memory barriers etc (c.f. the happens-before relationship in JMM [3] and other memory models). See for example [4] and [5]. [1]: https://en.wikipedia.org/wiki/Total_order https://en.wikipedia.org/wiki/Total_order [2]: https://en.wikipedia.org/wiki/Partially_ordered_set https://en.wikipedia.org/wiki/Partially_ordered_set [3]: https://en.wikipedia.org/wiki/Java_memory_model https://en.wikipedia.org/wiki/Java_memory_model [4]: https://www.youtube.com/watch?v=UYZIHP120go https://www.youtube.com/watch?v=UYZIHP120go [5]: https://www.microsoft.com/en-us/research/publication/time-clocks-ordering-events-distributed-system/ https://www.microsoft.com/en-us/research/publication/time-cl...

Waiting for the physicist in the room to point out: there is no such thing as simultaneity! :)

theNJR 6y ago

Came here to suggest The Order of Time by C Rovelli, which explains this in such a captivating way.

amelius 6y ago
I think this video explains the issue quite well in only two minutes: https://www.youtube.com/watch?v=wteiuxyqtoM https://www.youtube.com/watch?v=wteiuxyqtoM
- melenaboija 6y ago
  Another one here, it is in Catalan but with subtitles in english. Minute 18 is where it is explained although I think is worth it to watch all of it https://www.ccma.cat/tv3/alacarta/quequicom/tempus-fugit-subtitulat-en-angles/video/5540737/ https://www.ccma.cat/tv3/alacarta/quequicom/tempus-fugit-sub...
- Dylan16807 6y ago
  But that only happens with sufficiently high relative velocities. Earth and Mars are effectively in the same reference frame.

deleted 6y ago

[deleted]

Daho0n 6y ago

S/he already did. We just don't know yet.

extropy 6y ago
She both did and did not until we observe :p. And even that is not correct. Events happening propagate with speed of light - the event horizon. We can predict we will receive information of something happening, bit that's just prediction about future events, regardless of the location.
fckthisguy 6y ago
You can just say "they". (Not trying to be judgy. People just seem to forget about the gender neutral use of "they".)
- buzzerbetrayed 6y ago
  There are like 500 other ways you could have said what you just said as well. Doesn’t mean the way you said it is invalid.
- unanswered 6y ago
  Why is it acceptable to use the wrong pronoun, such as "they", for someone who chooses the pronoun "she" or "he"?
  - randomchars 6y ago
    > used to refer to a person of unspecified gender. How is this offensive to anyone??
    - unanswered 6y ago
      For the same reason referring to anyone with the wrong pronouns is, I would assume. Isn't that offensive? I didn't realize this was up for debate in 2021.
      - randomchars 6y ago
        But you're not referring to someone with the wrong pronoun, but using a gender neutral one.
        unanswered 6y ago
        I'm sorry, I honestly don't understand what distinction you're trying to point out. If someone's preferred pronoun is "she", for example, and I refer to her as a "they", then that's the wrong pronoun, isn't it? That's literally the definition of "wrong", at least the definition I understand. The right pronoun is "she" and other pronouns such as "he" and "they" and "it" are, by exclusion, wrong. But it seems like you're saying there's some kind of complex relation where sometimes people don't get to choose their own pronouns, but other people get to choose which one out of many to use based on convenience. Maybe it would help my understand if you could provide a chart relating the pronouns someone chooses with the pronouns other people are then allowed to use?

whatshisface 6y ago

Simultaneity is at least as well defined as clock time. Both clock time and the velocity of your reference frame can have arbitrary constants added to them to yield equally valid coordinate systems. So "it's not really simultaneous" is analogous to "it's not really 6:30 PM."

bregma 6y ago
Well, it's 6:30 PM somewhere. lifts glass
- UnpossibleJim 6y ago
  From The Hitchhiker's Guide to the Galaxy: "Time is an illusion. Lunchtime doubly so."

walrus01 6y ago

> simultaneity not in the true accurate to the picosecond sense of the word, no, but the exact word simultaneity is used when discussing number and density of satellites about a given latitude/longitude in the starlink beta program. Since they're LEO and orbiting at only 550 km, the satellites above a given spot on the ground vary greatly in the not-yet-complete sparse network. Usually related to discussions of whether a beta test customer terminal will briefly hiccup and lose connection to its default gateway, or if somebody is at a sufficiently high latitude that they can have full coverage for all 86400 seconds in a day. https://satellitemap.space/ https://satellitemap.space/ has a good animated visualization of this.

cphajduk 6y ago

Depends what type of physicist you ask. According to the energy-time uncertainty principle we don't even know when exactly the RF waves that transmitted information hit the receiver on Earth either.

cambalache 6y ago

Oh but there is. Just not in the same frame of reference.

avz 6y ago

In the absence of a physicist, I suppose that a software engineer in the room might do. After all, the counterintuitive consequences of relativity have their counterparts in counterintuitive effects in distributed systems and concurrent programming. In both cases, the core issue that misleads our intuition is the lack of a shared global clock that would impose a total ordering [1] on events/reads/writes/etc. Instead, events in both situations are only ordered partially [2]. In relativity the ordering is determined by the speed of light, in distributed systems the ordering is determined by what messages have been exchanged by two nodes and in concurrent programming reads and writes are ordered by synchronization actions such as lock acquisition and release, memory barriers etc (c.f. the happens-before relationship in JMM [3] and other memory models). See for example [4] and [5]. [1]: https://en.wikipedia.org/wiki/Total_order https://en.wikipedia.org/wiki/Total_order [2]: https://en.wikipedia.org/wiki/Partially_ordered_set https://en.wikipedia.org/wiki/Partially_ordered_set [3]: https://en.wikipedia.org/wiki/Java_memory_model https://en.wikipedia.org/wiki/Java_memory_model [4]: https://www.youtube.com/watch?v=UYZIHP120go https://www.youtube.com/watch?v=UYZIHP120go [5]: https://www.microsoft.com/en-us/research/publication/time-clocks-ordering-events-distributed-system/ https://www.microsoft.com/en-us/research/publication/time-cl...