4 ms·
when they say "it's currently 29000 light years away from earth", doesn't that mean that was its position 29000 years ago ?
by zzzeek 7y ago
when they say "it's currently 29000 light years away from earth", doesn't that mean that was its position 29000 years ago ?
- deleted 7y ago[deleted]
- chubbyrabbit 7y agoYes. However, it's like pointing at the sun and say "That's not the sun, the sun was there 8 minutes ago".
- likeliv 7y agoSince the sun isn't turning around the earth, I believe the sun is still where you point at.
- manigandham 7y agoTechnically the Sun is moving as part of the arms of the Milky Way galaxy, which itself is moving through space on a collision course with Andromeda, so where you point at will be off.
- afiori 7y agoThis would be unnecessarily pedantic but not wrong* if not that the heart rotates on itself, so you are pointing at a 8 minutes old direction. *All these discussion make no sense at all, as neither synchronous remote events nor the concept of what rotates around what are meaningful. This is not to say that we should not have this conversation, but to say that you are being pedantic without bringing anything to the table.
- gdubs 7y agoI’m listening to Carlo Rovelli’s book, “Reality is not what it seems”, and I’m still hung up on the concept of the “extended now”. The way he describes it, everything being relativistic, there’s no such thing as an “objective” point of view. So, if I understand his take on your example, we’re not seeing the sun as it was 8 minutes ago. It simply takes 8 minutes for the sun’s “now” to reach us.
- prab97 7y agoThat reminds me of a very important aspect of distributed systems (computer science) - there is no global clock!
- isostatic 7y agoUTC is a global clock. If I show the time in Sydney and the time here in UK, Sydney will be 150ms behind to me, and 150ms ahead to a viewer in Sydney, but I know the distance therefore I know if the clocks are in sync. The time dilation between the two places is on the order of femtoseconds/second, a millionth of a clock cycle of a cpu.
- pbhjpbhj 7y agoSounds to me like you could have equally started that post with "UTC is not a global clock".
- isostatic 7y agoIt's a global clock. UTC is the same time in Miami as it is in Singapore. The accuracy of the delivery of that timesource is 10ns in theory, and upto 1000ns in practice.
- pluma 7y agoCET and EST are also the same time in Miami as in Singapore. That's just how time zones work. The distinction with UTC is that it isn't tied to any particular physical location, it's not the "time zone" for anywhere. But UTC is ultimately defined by consensus. We need a reference clock and we need to be able to measure or estimate our skew in order to sync to it.
- swiley 7y agoHow do you know you have the correct (to the accepted precision) time?
- zzzeek 7y agoBy that definition there is no meaning to the word "now". If I'm five feet away from you, it takes time for light to travel between us. Snark aside, using the phrase "now" to describe an in-motion event that is observed over 29000 light years is misleading and should rather say "is now observed as 29000 light years away".
- ncallaway 7y ago> By that definition there is no meaning to the word "now". Yes, exactly! "Now" is an extremely useful concept on Earth, when we're all in approximately the same space going approximately the same speed. Now gets a lot done for us. Now is not really a concept on the universal scale. "There is no meaning to now" is a great take-away from general relativity!