It’s time to resume digesting this book, last post was from the end of October, two and a half months ago. At first I thought that it would be easy but now I realize that a decent post on that book might take twice the time – first to understand what it is talking about and then process it internally to form a presentable opinion. Some chapters are too esoteric but the one I have to resume from poses complicated science questions.
It’s about using Doppler effect to determine distance to stars and galaxies and measure the rate of the expansion of the universe. It comes after a chapter on using star luminosity to estimate distances and uses largely the same argument – it’s all relative, science makes assumptions first and then compares other data to the assumed standard to fill out the rest. If the luminosity of their “standard candle” star is wrong then all measurements comparing other stars to it should go into the bin, too. With Doppler effect it’s a bit more complicated but no less compelling in the end. To get to the end of the chapter, however, is hard.
I remember reading it for the first time and it made total sense, I moved on without any questions. On rereading, however, I realized that either the author is wrong or I’m totally confused about Doppler. Internet isn’t very helpful either.
Everybody learns about Dopper effect in school. The author uses the example of an ambulance but it’s best observed with trains, in my experience – because they are so much faster than ambulances moving through city traffic and because they emit sound of a constant tone unlike “wee-woo” of police and emergency vehicles. The best case is when the train blows its horn but it’s already loud enough to hear the increase in pitch as the train approaches and decrease when it goes away.
The book explains it in terms of moving objects velocity which affects the speed of sound but now I’m not so sure about that. When the book jumps to using Doppler effect to distances between us and stars it says that speed of light is constant therefore it’s not affected by the speed of stars and Doppler effect shows expansion of space instead. Say what?
What does “space expansion” mean? Do miles get longer or are there more miles between objects? If miles get longer then so should be kilometers, feet and everything else. How would it look any different?
Doppler effect with sound doesn’t affect speed of sound either, it’s still 300 m/s in air just like light is always 300 km/s in vacuum. Yes, sound can propagate faster or slower but that’s not what happens with Doppler.
Doppler effect doesn’t tell us the speed of light or sound either, it shows that distance between two crests of a wave increases or decreases – that’s what change in pitch or red or blue spectrum shifts are. With sound and objects moving close to its speed it takes significantly longer for sound to travel to our ears if the object moves away but with light the difference is negligible because our speeds are incomparably slower. Still, police uses Doppler radars to measure speeds of cars because it’s not the speed of radio waves that is affected but the difference between crests of the same wave. Radio is a radio but long waves are longer than 1 km – too long to catch speeding cars. Police radars use much shorter waves, less than 10 cm.
In light of the above the book’s objection seems invalid but that is only a first impression. I have to admit I don’t understand much of it at all. I’ve also learned that the formula for calculating Doppler shift in astronomy is different because it has to account for constant speed of light. The book is probably right and I’m wrong.
Never mind this little confusion, it’s the rest of the chapter that is rock solid and should be remembered.
When applying this method scientists assume that stars don’t transmit Doppler shift themselves and attribute it to expansion of the universe. They have a theory to explain this expansion, ie Big Bang, but we might just as well ask for a theory where stars would transmit Doppler shift and no expansion would be necessary.
Historically, the theory of expansion was sounded first, the observation was then interpreted on the basis of this theory, and then they declared that this interpretation confirmed it.
However, in science data always underdetermines a theory, that is data can be interpreted in several valid ways, and therefore it’s impossible to determine which theory is correct on the basis of data itself. If there was a theory explaining Doppler shifted transmission from stars themselves it would have explained all the data just as well. We don’t have that theory and don’t even try for it because we believe that stars and laws which govern their transmissions are uniform everywhere in the universe. We assume that stars behave just like objects in our lab experiments and their red light, for example, is caused by the same chemical reactions as red light produced in our labs.
Without the assumption of uniform universe all our theories about stars and distances between us would be useless. We can’t even contemplate the world where this assumption doesn’t hold. Obviously, it does not hold in Sāṅkhya but scientists got problems even without us telling them so.
The principle of underdetermination means that scientists have to pursue all plausible and internally consistent theories at the same time until they find data that doesn’t fit and eliminate those theories one after another. This doesn’t happen in real life, alternatives are rarely pursued with the same vigor and when new data comes in which doesn’t conform to a theory nothing gets eliminated but the theory gets patched instead to account for anomalies.
Patched here means adding new assumptions, quite arbitrarily, simply because they would explain it better. In case of Doppler shifts new data shows not just expansion but accelerated expansion and accelerated expansion is impossible according to general relativity. What was the patch? Introduction of “dark energy”? How big is the input of this dark energy to expansion? 68% – over two thirds, but it keeps general relativity correct. I mean as long as you are content with the fact that some new and undeveloped theory accounts for two thirds of the time when general relativity is wrong. How new is this theory? Well, they gave Nobel Prize for discovery of acceleration only in 2011, basically five years ago. There’s no theory as such yet.
Are they going to admit that general relativity does not comply with experimental data and therefore should be abandoned? Nope, they are not even going to modify any time soon.
Science knows everything, right?