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Most Distant Objects

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Posted by Daniel Johnson on November 26, 2002 12:52:54 UTC

The distances stated by astronomers are estimates of how long the light has taken to reach us, not how far away the object is "now." We have no idea whether those objects still exist as identifiable objects now, or whether the galaxies seen have collided with others, etc. Strictly speaking, the "distance" is a measure of the age of the light that we see, not the distance to the object.

When they speak of the most distant objects visible, astronomers are very much conscious of something we usually ignore: we see something as it was when light left it, not as it is now. Light travels about a foot per nanosecond, so someone 10 feet away from you is at a distance of ten light-nanoseconds, and the light hitting your retina is "old" light, aged 10 nanoseconds. To us that's inconsequential, but in astronomy/cosmology, distance is time. We ALWAYS look into the past, and CANNOT see "now." This is true in everyday life and in astronomy, but obvious only at astronomical distances. And of course, regardless whether one accepts the Big Bang or some other less likely theory, it is not possible to see an object further away in light-years than the age of the universe, since its light could not have reached us yet.

The distance/time estimates are merely that: estimates. Astronomers sometimes speak of distance in terms of redshift (for example, "It's at a redshift of 2.2"), since the redshift is a measured fact, but the relationship of redshift to distance (or, if you prefer, the relationship of redshift to the age of the light) is constantly being fine-tuned with further research.

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