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Do It Yourself

Entry 1840, on 2017-03-03 at 21:47:43 (Rating 3, Science)

I was going to post this comment as part of an anti-creationist rant but I realised that there was so much to it that I really needed to post it as a separate item. The issue I wanted to tackle was how many believers in mysticism base their beliefs on revealed sources, such as holy books, but the same criticism could be made against "rational" people, like myself, because I also use sources (such as science books, Wikipedia, etc).

So basically what I wanted to do was to show that anyone can discover significant things about the real world by themselves without relying on any information from existing sources, and that they can show anyone how to do the same observation/experiment which would prove their point beyond any reasonable doubt.

I decided to choose the age of the universe as a suitable subject, because it was a controversial subject (there are many young Earth creationists), and it was relatively easy to test. Of course, as I intimated above, it got more complex than I imagined. However, here is my proof - which anyone with a bit of time and a small budget can follow - that the universe, and therefore the Earth, is much older than the 6000 years the young Earth creationists claim.

I could start by trying to establish the age of the oldest things I know of. I could use biology, archaeology, chemistry or physics here, but I know a bit more about astronomy, so let's use that.

We know the light from stars travels through space at the speed of light. If the stars are far enough away that the light took more than 6000 years to get here then the universe must be more than 6000 years old, so creationism is wrong. I know there are some possible objections to these initial assumptions but let's leave those aside for now.

First, how fast is the speed of light? Can I figure this out for myself or do I need to take it on trust (some would say faith) from a book? Well it is actually quite easy to figure this out because we can use a highly regular event at a known distance to calculate the time it took for light to reach us. The most obvious choice is timings of Jupiter's moons.

The moons of Jupiter (there are 4 big ones) take precise times to complete an orbit. I can figure that time out by just watching Jupiter for a few weeks. But we would expect a delay in the times because the light from an event (like a Moon going in front of or behind Jupiter) will take a while to reach us.

Conveniently, the distance from the Earth to Jupiter varies because some times the Earth and Jupiter are on the same side of the Sun, and others the opposite side. So when they are on the same side the distance from the Earth is the radius of Jupiter's orbit minus the radius of the Earth's, and when they are on opposite sides it is the radius of Jupiter's orbit PLUS the radius of the Earth's. Note that the size of Jupiters orbit doesn't matter because the difference is just double the size of the Earth's (in fact it is double the radius, or the diameter).

So now we need to know the size of the Earth's orbit. How would we do that? There is a technique called parallax which requires no previous assumptions, it is just simple geometry. If you observe the position of an object from two locations the angle to the object will vary.

It's simple to demonstrate... Hold your finger up in from of your eyes and look at it through one eye and then the other. The apparent position against a distant background wall will change. Move your finger closer and the change will be bigger. If you measure that change you can calculate the distance to your finger with some simple maths.

In astronomy we can do the same thing, except for distant objects the change is small... really small. And we also need two observing locations a large distance apart (the further apart they are, the bigger the change is and therefore the easier it is to measure). Either side of the Earth is OK for close objects, like the Moon (a mere 384000 kilometers away) but for stars (the closest is 42 trillion kilometers away) we need something more. Usually astronomers use the Earth on either side of its orbit (a distance of 300 million kilometers) so the two observations will be 6 months apart.

So getting back to our experiment. You might think we could measure the distance to a star, or a planet like Jupiter, or the Sun using this technique but it's not quite so simple because the effect is so small. What we do instead is measure the distance to the Moon (which is close) using parallax from two widely separated parts on the Earth. I admit this needs a collaborator on the other side of the Earth, so it involves more than just one individual person, but the principle is the same.

Once we know that it can be used to measure other distances. For example, if we measure the angle between the Moon and Sun when the Earth-Moon-Sun angle is a right angle we can use trigonometry to get the distance to the Sun. It's not easy because the angle is very close to 90 degrees (the Earth-Sun side of the triangle is much longer than the Earth-Moon side) but it can be done.

So now we know the difference in distance between the Earth and Jupiter in the two situations I mentioned at the start of this post. If we carefully measure the difference in time between the timings of Jupiter's Moons from Earth when Earth is on either side of its orbit we get a difference of about 16 minutes. So light is taking half of that time to travel from the Sun to the Earth. We know that distance from the previous geometric calculations, so we know the speed of light.

Note that none of this is open to any reasonable criticism. It is simple, makes no assumptions which can fairly be questioned, and anyone can do it without relying on existing knowledge. Note that if you want to derive the basic trig calculations that is fairly easy too, but few people would argue about those.

So the Sun is 8 light minutes away meaning the light we see from the Sun left it 8 minutes ago. We are seeing the Sun literally as it was 8 minutes in the past. This means it must have existed 8 minutes in the past. But who cares? Well this is interesting but looking at more distant objects - those not just light minutes away but light years, thousands of light years, millions of light years away say more about the true age of the Universe.

So we can use this idea in reverse. Above we calculated a distance based on a time difference and the speed of light. Now we will calculate a time based on distance and the speed of light. If a star is 10,000 light years away the light left it 10,000 years ago, so it existed 10,000 years ago, so the universe is at least 10,000 years old.

There is only one direct method to calculate distance and that is parallax. But even from opposite sides of the Earth's orbit - a baseline of 300 million kilometers - parallax angles are ridiculously small. But with a moderate size telescope (one which many amateurs could afford), and careful observation, they can be measured. The parallax angle of the closest star is about 800 milliarcseconds, or 0.01 degrees. That gives an angle which is the equivalent of the width of a small coin about 5 kilometers away.

Do this observation, then a simple calculation, and the nearest star turns out to be 40 trillion kilometers (4 light years) away. When we see that star we see it as it was 4 years ago. In that time the star could have gone out or been swallowed by a black hole (very unlikely) and we wouldn't know.

The greatest distance so far detected using parallax is 10,000 light years, but that was with the Hubble Space Telescope, so that is beyond the direct experience of the average person! However note that using this direct, uncontroversial technique, the universe is already at least 10,000 years old, making young Earth creationism impossible.

Another rather obvious consequence of these distance measures is that stars are like our Sun. So if we know how bright stars are we can compare that with how bright they appear to be and get a distance approximation. If a star looks really dim it must be at a great distance. The problem is, of course, that stars vary greatly in brightness and we can't assume they are all the same brightness as the Sun.

There is another feature of stars which even an amateur can make use of though - that is the spectrum. Examining the spectrum can show what type of star produced the light. The amateur observer can even calibrate his measurements using common chemicals in a lab. The chemicals in the star are the same and give the same signatures (approximately, at least).

So knowing the type of star gives an approximation of the brightness and that can be used to get the distance. The most distant star visible to the naked eye is 16,000 light years away. This would be bright enough to get a spectrum in a telescope, determine the type of star, and estimate the distance. Of course, it would be hit and miss trying to find a distant star to study (because we're not supposed to use any information already published) but enough persistence would pay off eventually.

There are objects in the sky called globular clusters. These are collections of a few hundred thousand to a few million stars, quite close together. To the naked eye they look like a fuzzy patch but through a small telescope they can be seen to be made of individual stars. A simple calculation based on their apparent brightness shows they are tens of thousands of light years away. A similar technique can be applied to galaxies but these give distances of millions of light years.

In addition, an amateur with a fairly advanced telescope and the latest digital photography equipment - all of which is available at a price many people could afford - could do the investigation of red-shifts originally done by Edwin Hubble over 100 years ago.

A red shift is the shift in the spectrum of an object caused by its movement away from us. As I said above, the spectra of common chemicals can be tested in the lab and compared with the spectrum seen from astronomical objects. As objects get more distant they are found to be moving away more quickly and have higher red shifts. So looking at a red shift gives an approximate measure of distance.

This technique can only be used for really distant objects, like galaxies, so it is a bit more challenging for an amateur, but it will give results of millions to billions of light years, meaning the objects are at least millions or billions of years old.

There are some possible objections to everything I have discussed above. First, maybe the speed of light was much faster in the past meaning that the light could have travelled the vast distances in less time than assumed, meaning the universe could still be just 6000 years old.

Second, the light from the objects could have been created in transit. So a galaxy could have been created 2 million years ago but its light could also be created already travelled 99% of the way to the Earth.

Finally, maybe there is a supernatural explanation that cannot be explained through science or logic, or maybe all of the evidence above is just the malicious work of the devil trying to lead us all astray.

The second and third objections aren't generally supported, even by most creationists, because they imply that nothing we see can be trusted, and God is not usually thought to be deliberately misleading.

The first one isn't totally ridiculous though, and there is some serious science suggesting the speed of light might have been faster in the past. But do the calculations and that speed would have to be ridiculously fast - millions of times faster than it is now. If it was changing at that rate then we would see changes over recorded history. So that claim could also be checked by anyone who was prepared to dig into old sources for timings of eclipses, the length of the day, etc.

Astronomy is an interesting science because so much of it is still do-able by amateurs. Follow the steps above and not only will you get a perspective on some of the greatest work done in the past, but you will also make for yourself a truly fundamental discovery about the universe: that it is really old.

It requires no faith in authority, no reference to trusted texts, and no unfounded assumptions. It just involves a few years of dedicated observation and study. I admit I haven't done all of this myself, but it's good to know I could if I wanted to.

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