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The supernova occurred when the year on Earth was 1381, and the light from that event took 642.5 years to reach us, just like from our perspective it takes 10 h

The supernova occurred when the year on Earth was 1381, and the light from that event took 642.5 years to reach us, just like from our perspective it takes 10 hours to send a transmission to Voyager 1; I don't think anyone agrees it would be 'more correct' to say that Voyager transmitted its reponse in the instant that we receive it on Earth, rather than 10 hours prior. This is how I've seen astronomers routinely describe both of these things, so even if it is a simplification I don't think either of my statements are wrong. I think the 'on Earth' was implied; I doubt anyone who read that thought I was referring to the passage of time from the perspective of the photon, for example.

jbotz 3y ago
> The supernova occurred when the year on Earth was 1381 This is the part that is wrong. The supernova (would have) occurred in Betelgeuse's reference frame which doesn't have such a direct correspondence to Earth's. > just like from our perspective it takes 10 hours to send a transmission to Voyager This is different because here we are talking about half a round-trip time for the signal. Ultimately the 'speed of light limit' is about information. And for us to pass information to Voyager and then receive a response takes 20 hours in our reference frame. So when you're talking about round trips it makes sense because the start and finish are in the same reference frame.
- calgarymicro 3y ago
  > reference frame which doesn't have such a direct correspondence to Earth's If we choose Earth as a fixed reference point (which astronomers definitely do for cosmic events, I've read too many articles where they do that to think that they don't), it still seems to me that my statement is correct; at the very least, it's the way I've seen every astronomer who's ever discussed it express this, and I've never seen any subject matter experts take such an issue with this framing. If you wanted, you could scale this problem down a lot, to someone on the ground vs. on the ISS. You could even scale it down to a fiber optic cable unspooling between two cars driving at different speeds. At some point, we're still picking a reference frame to count the seconds in. > This is different because here we are talking about half a round-trip We don't have to just talk about round trips though. Voyager can also send us transmissions unprompted, and I still doubt anyone would think it's more correct to say that it begins transmissions in the instant we receive them, rather than 10 hours prior (especially because Voyager timestamps it's transmissions with Earth time, or at least what it thinks is Earth time).

jbotz 3y ago

> The supernova occurred when the year on Earth was 1381 This is the part that is wrong. The supernova (would have) occurred in Betelgeuse's reference frame which doesn't have such a direct correspondence to Earth's. > just like from our perspective it takes 10 hours to send a transmission to Voyager This is different because here we are talking about half a round-trip time for the signal. Ultimately the 'speed of light limit' is about information. And for us to pass information to Voyager and then receive a response takes 20 hours in our reference frame. So when you're talking about round trips it makes sense because the start and finish are in the same reference frame.

calgarymicro 3y ago
> reference frame which doesn't have such a direct correspondence to Earth's If we choose Earth as a fixed reference point (which astronomers definitely do for cosmic events, I've read too many articles where they do that to think that they don't), it still seems to me that my statement is correct; at the very least, it's the way I've seen every astronomer who's ever discussed it express this, and I've never seen any subject matter experts take such an issue with this framing. If you wanted, you could scale this problem down a lot, to someone on the ground vs. on the ISS. You could even scale it down to a fiber optic cable unspooling between two cars driving at different speeds. At some point, we're still picking a reference frame to count the seconds in. > This is different because here we are talking about half a round-trip We don't have to just talk about round trips though. Voyager can also send us transmissions unprompted, and I still doubt anyone would think it's more correct to say that it begins transmissions in the instant we receive them, rather than 10 hours prior (especially because Voyager timestamps it's transmissions with Earth time, or at least what it thinks is Earth time).