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The Hubble Telescope's "Pillars of Creation"

07/04/08 | by Adam | Categories: Technology

Link: http://harvardmagazine.com/2008/07/eye-on-the-universe.html

The Harvard Magazine has a good write-up on the Hubble Telescope and includes a couple of photos. One of the photos is a stunning picture of "The Pillars of Creation" in the Eagle Nebula. The explanatory text says:

This is a ghost image of a past cosmic disaster that we won’t see here on Earth for another thousand years or so—and a perfect example of the fact that everything we see in the universe is history.

This has me scratching my head. I -- more or less -- get the relativity angle in that it takes time for light to reach Earth across the magnitudes of space and therefore when we see something it means it's already long since happened. What I don't understand is the implication how we can see a ghost image before we see the real thing? With the speed of light being the limiting factor, how can we see results before the original happening?

I've run up against a similar "I don't get it" before. Back in 1999, Alan Parsons released a quite good album called "The Time Machine" which included the following narration from Professor Frank Close (www.theavenueonline.info/site3/lyrics/temporal.htm):

When you look out into the night sky, and you see the stars far away, you're seeing them because of the light that has traveled from them to you.

But it takes time for the light to travel here. So what we're doing is seeing the stars as they were in the past, in the amount of time it has taken for the light to reach us. The further, and further away the stars are, the further back in time we're looking.

Now we're seeing a star that, let's say, is 6,000 years ago. Imagine somebody on that star looking at us. They would be seeing us as we were 6,000 years ago.

Which of those two is "now"?

So space and time are linked together. We are looking across the space, we are looking back in time.

It's the "now" question and explanation that bothers me. Just because I can't see what you're doing for a bit, and you can't see what I'm doing for a bit, it doesn't mean that what I'm doing happens when you observe it or vice versa. Therefore "now" is not relative but absolute as otherwise there's a wonderful paradox going on. This is probably why I'm not a physicist; there are just some things I simply cannot get my mind around.

Anyway, for a rather more prosaic example of observation and the speed of information, take a look at this article on the firing gun giving a measurable advantage to sprinters marginally closer to it. (Via Kottke)


1 comment

Comment from: Nimble [Member]  

The particular article you linked to isn’t the clearest about what they mean.

What’s happening there is that there is a shockwave that we can observe traveling towards the Pillars, and we will see it hit them in an estimated 1,000 years, presuming we haven’t gone all MORLOCK+ELOI in the interim.

Since the nebula is about 7,000 light years away, the actual destruction of the Pillars would have already taken place 6,000 years ago.

I can whip up something with light cones and such, but they just went for an over-cute analogy that confuses the “whens” of things happening :)

07/05/08 @ 05:18
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