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## Time and distance

July 21st, 2003

The frontpage of Monday’s SMH has a link to a multimedia piece, entitled “Journey to the Centre of the Universe”. I couldn’t make the link work, but the teaser text says everything I needed to know anyway. I reproduce it without comment

Take a spectacular 3D tour to the centre of our solar system. Normally it would take you 50 million light years, but we can get you there in three minutes.Ê

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1. July 21st, 2003 at 20:53 | #1

I bet the person who wrote that was only 48 kilograms high.

2. July 21st, 2003 at 21:26 | #2

I don’t think you’re treating the journo with sufficient gravity.

3. July 21st, 2003 at 22:29 | #3

I don’t actually have a problem with this usage; a “light year” is a measure of the time it takes you to get somewhere if you’re travelling at the speed of light. To claim that it is therefore *only* a measure of distance is to use grammar to bring in exactly the frame-of-reference centrism that Einstein proved was illegitimate.

4. July 21st, 2003 at 23:38 | #4

dsquared,

I might have to think that one over for a few million light-kilometers.

5. July 22nd, 2003 at 00:50 | #5

Maybe I should start quoting my weight in terajoules on the basis E=Mc^2.

6. July 22nd, 2003 at 10:28 | #6

since when is our sun the centre of the universe anyway?

7. July 22nd, 2003 at 10:52 | #7

In connection with the Costello post, I was about to ask whether 16 July was really two weeks ago.

But now I realise that such scepticism would have been merely another instance of the ‘frame-of-reference centrism that Einstein proved was illegitimate’.

Thanks, d^2.

8. July 22nd, 2003 at 12:51 | #8

Gianna, I was waiting for someone to mention the second glaring error. BTW, I didn’t take my camera!

9. July 22nd, 2003 at 13:58 | #9

The way an amateur astronomer reads this:

The center of our solar system is some light days away. 50M L.Y. is the distance to the center of the galaxy from the edge of it. We are ~1/3 of the way in from the edge.

10. July 22nd, 2003 at 14:23 | #10

Actually it’s only about 8 light minutes and 20 light seconds 😉

11. July 22nd, 2003 at 16:04 | #11

>>In connection with the Costello post, I was about to ask whether 16 July was really two weeks ago.

Quiggin’s clearly spent the last week travelling at roughly 75% of the speed of light.

12. July 23rd, 2003 at 02:38 | #12

Once more I step to the defence of these guys by pointing out that a heliocentric frame of reference is as valid as any other on scientific grounds.

13. July 23rd, 2003 at 03:29 | #13

I’ve been thinking about a new name for this blog. Maybe I should go for “The Blog at the Centre of the Universe”.

14. July 24th, 2003 at 12:06 | #14

you don’t mean the Blog at the End of the Universe, do you, John (with apologies to Douglas Adams)? if so, can I please order a pan-galactic gargleblaster.

15. July 24th, 2003 at 23:44 | #15

dsquared:

a “light year” is a measure of the time it takes you to get somewhere if you’re travelling at the speed of light.

No, if you’re travelling at the speed of light it takes you zero time to get anywhere.

a heliocentric frame of reference is as valid as any other on scientific grounds

Which is why describing the solar interior as the centre of the Universe is a serious conceptual error. In other news, I intend making a trip to the centre of the Universe this evening, in a coordinate system centred on the Alma bar.

16. July 25th, 2003 at 20:58 | #16

>>No, if you’re travelling at the speed of light it takes you zero time to get anywhere.

Why is there a delay on satellite phone links then? You’ve misremembered this one mate.

17. July 27th, 2003 at 05:01 | #17

dsquared:
>>Why is there a delay on satellite phone links then? You’ve misremembered this one mate.

If you were the signal you’d take zero time; if you were the wankerphone you’d have to wait.

18. July 29th, 2003 at 01:24 | #18

But if I was the signal I’d have zero mass. If I was a massive object being accelerated to the speed of light, time would dilate for me but my subjective time to travel one light year would be one year in the limit, wouldn’t it?

19. July 30th, 2003 at 16:41 | #19

Urhhh!

From the POV of an outside observer, arbitrarily assumed to be at zero-velocity, your time would slow down as you accelerated toward the speed of light. Looking out, you would see the universe aging a lot more quickly, plus there would be a variety of doppler shift and other effects you would see. The faster you went, the greater your mass would be, until at c itself you would have effectively infinite mass. You’d also have zero length, which is a troubling concept. And you’d get wherever you were going in zero seconds of subjective time, regardless of how things might look to someone outside your frame of reference.