RE: some questions about the age (of earth, universe, etc.)
June 9, 2011 at 2:32 pm
(June 9, 2011 at 1:28 pm)Zenith Wrote: I know I once read something about the subject, but I remember it was quite vague and wasn't too much about it.
I'm interested in these issues (and I suppose some of you can give me some answers or some links for answers):
1. How is the age of the universe calculated?
2. How is the age of our earth calculated?
3. How do people measure the distances between stars and other celestial objects? (I'm mostly interested in those that are very far away).
P.S. If this is important, know that I do not have very advanced knowledge of physics, nor know too many things about cosmology (well, if I knew too much about cosmology then I wouldn't have asked these questions)
For your question 1 and 3, you need some background knowledge to make sense of any answer. So here we go: The calculation of the age of the universe, the determination of the composition of the very far objects like stars and galaxies, the measurement of distance to very far stars, and measurement of the speed with which a very far star is approaching and receeding from us are intricately related.
1. The composition of the atmosphere of a star, gases in galaxies, and such can be determined by looking for unique patterns of bands of light or darkness in the spectrum of their light. This pattern is called obsorption lines. What element makes what absorption patterns is easy to determine in the laboratory.
2. How fast a star is approaching and receeding from us can be determined by looking at how far the particular patterns of obsorption lines is displaced from their normal position in the electro-magnetic spectrum, which can be determined easily in the laboratory. The displacement of the obsorption lines exhibits a property called doppler effect. Obsorption lines of objects receeding from us shifts to the red side of spectrum, those of objects approaching us shifts to the blue side. For simplicity let's call them, as astronomers do, red shift and blue shift. The greater the red shift, the faster the recession.
3. How far any arbitray isolated star is from us is normally hard to determine, but when particular type of star explodes the distance to the explosion is easy to determine. This type of explosion is called type I super nova, and all type I super nova falls within an very narrow range of brightness. Type I super nova is thus called a "standard candle". If you know how bright a candle is close up, and you can measure how bright it appears to you from the distance, you can immediately determine what that distance is. Similarly if you see a type I super nova exploding, and you can measure its brightness as seen by you, then you know how far it is. Most stars occur in galaxies. So if you see a type I super nova exploding inside a galaxy, you know how far that galaxy is from us, and hence how far all the stars of that galaxy is from us.
We can combine distance measurement via type I super nova, and speed of recession measured via red-shift into a single plot, we find a very powerful pattern. The farther a distant galaxy, the faster it is receeding from us. Sparing you of complications, the age of the universe can thus be measured in principle by tracing backwards in time, and finding how long ago it must have been when the the receeding galaxies where together at the same point. The current best estimate is that was 13.1 billion years ago. So the universe in a form similar to ours was created 13.1 billion years ago.
For your question 2, some background in radioactive decay is needed. All radioactive elements are in the process of transforming themselves into another element. The rate at which the transformation occurs is directly observed in the laboratory to be essentially invariant, and indirectly inferred to be unchanging by noting that their effects had been the same far back in time. Consequently, it you know the rate at which a particular original radioactive element is changing to another resultant element, and you can measure how much of the original element still remain, and how much of it has already changed to the resultant element, then you know how long the original elements have been changing. Ratioactivity thus makes minerals containing both the original and resultant elements into a kind of clock, able to tell when the resultant elements first started to accummulate inside the minerals.
Now when the earth, or indeed the whole solar system, was first forming, we have powerful reasons to believe many types of minerals containing radioactive elements have had any previously accummulated resultant elements purged. Thus for these minerals their radioactive clock was reset to zero. By measuring how much the radioactive clock has run since, we know how old the earth, the moon, etc, is. The best estimate of the age of the earth currently is 4.56 billion years.
Currently there is no good estimate on how long it will be before creationists stop putting out bullshit in defiance of these realities.
