Just read this acticle, which says that hubble has obtained an image of so distant its from only 750 million years after the big bang.
Does this mean that the universe is expanding at a significant percentage of the speed of light? The latest estimate of the age of the universe is about 15 billion years (give or take about 5 billion). If light that set out 14,250,000,000 years ago is just reaching us now, it must have travelled 14,250,000,000 light years. I thought the big bang is assumed to have occured at a single point. If thats true then the objects imaged by hubble must have been travelling away from us at an average speed of 14,250,000,000/15,000,000,000 * 100 = 95% of the speed of light.
Is this calculation correct, or am I missing something (like, gulp, general relativity)?
The farther away that an object is, the faster it is moving away from us. I don’t know about the exact calculation, but an object 14 billion light years from Earth is moving away from us at a significant fraction of the speed of light.
Distances to galaxies and quasars are actually measured in redshift, not lightyears. I’m not sure of the latest numbers, but the highest value a few years ago was at least 5. If we could ignore the expansion of space, that would correspond to a speed of 95% of light speed, which is the same value you got.
Yes, you’re missing something. Yes, it’s general relativity.
Since the universe is expanding, finding the “distance” to a distant object is problematic. We are seeing it at a much earlier time. By “distance”, do you mean the distance it would be now if we could see where it is now? The distance it was from Earth 14,250,000,000 years ago? The distance the light has actually traveled to get to us? The last one makes the most sense, but it means knowing the rate of expansion of the universe for the last 14,250,000,000 years. In other words, “distance” depends on your model of how the universe is expanding.
Also, the Big Bang didn’t happen at one point, it happened at every point in space. Search Great Debates for “expansion of universe” and you’ll find a lot of threads that discuss this.
The current theory is that the universe expanded at faster than the speed of light, that is, there are currently some areas of the universe that we still can’t see yet since it’s more than 15 billion light years away. It’s allowed to do this since it’s space, not matter.
Actually, the latest estimate (from WMAP) is about 13.7 billion years (give or take about 0.2 billion).
FriendRob, the OP never once mentioned the word distance. Uncivil actually said that the light travelled 14.25 billion light-years (although it should be more like 13 billion). Just because you can’t put a measuring tape measuring off 14.25 billion light-years between us and the object doesn’t mean this statement is unreasonable.
You can go back even farther than that galaxy. The oldest thing (and I use that term loosely) is the cosmic background radiation, which was emitted when the universe was only about 300,000 years old. If you can figure out why we see this in every direction, I think you’ll have your question figured out. Me, I just accept it, not understand it.
To clarify, like Achernar said I was only talking about the distance the light from this object has travelled to reach us, not how far away the object actually is now.