It is now 100 years since the British scientist Arthur Eddington performed one of the most important experiments in modern physics which confirmed Einstein’s Theory of General Relativity. He observed a total solar eclipse from the island of Principe, off the west African coast. Basically this confirmed that space (and time) really are bent by mass (in this case, the Sun) as Einstein predicted.
The reason we don’t usually see this effect is that it is very small. Even a large mass like the Sun only distorts space a small amount so it was necessary to observe stars which were really close to the Sun (or appeared to be close because they were in line). Usually these stars aren’t visible because the light the Sun is so much greater than the distant stars (even though the stars could easily be intrinsically brighter) so the eclipse was used to block the Sun’s light.
OK, so there’s my little history, physics and astronomy lesson but what is the point of all this? Well there are certain experiments, observations and theories which just keep coming up in discussions of science. These experiments are so revolutionary and far reaching that, even years after they were carried out, they still get mentioned in discussions of the relevant fields of science. So I started thinking about what other experiments might be in that category.
The first one I thought of, and another one which is very topical (because of the 150th anniversary of its publication), is the Theory of Evolution. This wasn’t really the result of an experiment, it was more about careful and meticulous observation and recording, but I still think it ranks as one of the greatest scientific breakthroughs ever.
Another one which comes up a lot in physics and cosmology is the Michelson-Morley experiment. It was performed in 1887 by Albert Michelson and Edward Morley at what is now Case Western Reserve University. It was designed to detect the ether, which physicists at the time hypothesised the existence of because they needed a medium for wave phenomena, such as light, to travel through. The experiment showed the ether didn’t exist, although this was so unexpected to some physicists that there were various attempts to rationalise the result.
A more modern example (and those are difficult because great experiments usually only become obvious after their influence has lasted many years) is the observations of the cosmic microwave background by various satellite observatories, especially the Wilkinson Microwave Anisotropy Probe (WMAP). This mission was launched on 30 June 2001 and helped establish many important characteristics of the Universe, including its age to an accuracy of 1%. WMAP is still working and recent observations of anomalous areas of low temperature could be very significant in the future.
Another older result would be Hubble’s (I mean the astronomer, not the telescope which was named after him) observations which showed the Universe was expanding. I do seem to be mainly concentrating on physics and cosmology here but that has always been one of my major interests so I guess that’s inevitable. Hubble performed some remarkable precision measurements of galaxies which showed they were all (or almost all) racing away from us. This showed the Universe was expanding which was contrary to what most people thought at the time (including Einstein).
I’ve got to mention one last experiment which is one of my favourites of all time. And it is related to quantum physics, of course! Its the infamous double slit experiment which demonstrates: how particles are waves and waves are particles, but maybe they’re neither or both depending on the conditions; how one particle can be in two places at the same time; and how particles change their behaviour depending on whether they are being “watched” or not.
This experiment is still a mystery: not only can’t we explain it but I don’t think we even know what it means! Richard Feynman (one of the greatest quantum physicists) often said that all of quantum mechanics can be gleaned from carefully thinking through the implications of this single experiment.
Unfortunately, even though its been thought about a lot, quantum mechanics is not only the most successful theory but also the hardest to believe! It seems that reality at its deepest level seems totally unreal to humans who are used to thinking at the macroscopic level.
Finally, what will be the next great experiment? I think we need to know two things (again I’m sticking to the big picture – which is cosmology). First, what is dark matter and dark energy, and second (and most impotrant of all) how do we devise a theory which incorporates both quantum theory and relativity? Yes, its the old theory of everything again. We need an experiment to establish whether string theory or other alternatives can be used for the “theory of everything”. There’s no sign of that happening yet but one day it will.
As I continue to struggle through the task of listening to over 100 episodes of the AstronomyCast podcast (about 30 minutes each) I find more new and interesting ideas being presented. The podcast is a good one – the general level is not overly complex but it isn’t dumbed down either. I have noticed a few errors and misleading statements but its easy to be overly critical – even of a professional astronomer – because she is discussing ideas outside of her specialist area.
Minor errors aside, I do recommend this podcast if you are interested in astronomy because it is useful for both beginners and more experienced amateurs. It has been years since I taught astronomy myself and its amazing how much has changed in that time. I first discussed this in a blog entry titled “Things Have Changed” from 2009-02-16 and have mentioned it a few times since.
The latest thing which I have noticed has changed is our understanding of the size of the Universe. I can remember that the standard way to teach this in the 80s was to say the Universe had a radius of less than 14 billion light years because that was the maximum distance it could have expanded at less than the speed of light in the time available (its age at the time was estimated at 14 billion years).
Well things have changed since then. The age was quite accurate – we now say it is 13.7 billion years – but the rest is very different!
Here’s one current interpretation of the size of the Universe: the observable Universe is 78 billion light years in radius and that part is only about 1% of the total. To make things worse, the Universe we can see is only composed of 5% of stuff we understand quite well – the rest is dark matter and dark energy which is not well understood currently.
If you want to be more speculative still you can hypothesise the existence of a multiverse, as I discussed in “Is There a Multiverse?” from 2009-03-03, but even without that its obvious that the Universe is a lot bigger that we used to think (the multiverse theories usually say it is infinite).
But to get back to the commonly accepted values above. How can the radius be more than the age? Doesn’t that mean the Universe expanded faster than light? Well, yes, it does actually. Space is allowed to expand at any speed. Its only physical objects which can’t exceed the speed of light. So an object which emitted light 13 billion years ago could now be much more than 13 billion light years away because the space between it and us has expanded so much.
And the 99% of the Universe being invisible is a result of the ultra-fast expansion during the inflationary period. Star light (or anything else) from that part of the Universe will never reach us because the space between it and us is expanding too fast.
As I said in previous comments on the subject, the Universe just keeps getting bigger and more mysterious and our part in it seems to get less and less significant. But that’s just what we would expect based on history.
For many years now there has been a theory that our universe might just be one of many – in fact probably one of an infinite number – of other universes. The Big Bang would be an event where our universe formed inside a multiverse and that other universes with different properties would also exist in parallel to ours.
Recently I have seen more discussion of the idea and it seems to be being taken a bit more seriously now. The latest source was an article in New Scientist: “Dark flow: Proof of another universe?” from 23 January 2009 which provided a possible way to test the idea.
If you have been following current issues in astronomy and cosmology you will no doubt have heard of dark matter and dark energy. These two have caused a lot of trouble because they constitute 95% of the mass of the universe but we really don’t know what they are. Dark matter is material which only interacts gravitationally and clumps on large scales causing gravitational effects on galaxies. Dark energy is a uniform force causing the universe to expand faster as time passes.
As if those weren’t enough we now have dark flow! This seems to be the observation that galaxy clusters are moving towards a specific spot in space (this is independent of the general expansion of the universe) and again, we don’t know why. One possibility is that it is caused by large structures beyond the observable edge of our universe. Another is that the force is from another universe.
I must say I like the multiverse idea from a philosophical perspective because it eliminates many problems with the older Big Bang hypothesis where our universe was all there is and it, including time and space, was created from nothing in the Big Bang.
The problems were: how did the universe originate from nothing, what caused the Big Bang, why does our universe have the special physical laws and constants which make it possible for life to evolve, and what happens before and after the universe (if that even means anything).
If there is a multiverse then presumably it is infinite in time and space. Fluctuations in its material cause new universes to be created constantly. Each universe has its own laws and there are infinitely many, so having one with the exact laws and constants we have is not only possible, it is certain. And the “cosmic bubbles” which become universes continue on infinitely in the past and future so universes always exist.
As I said, its very neat from a philosophical perspective but is it science? Well, being able to test a theory is a major requirement of science. If a theory can’t be tested then we just endlessly speculate on it as a possibility, like philosophers tend to do, without making any real progress. I didn’t think multiverse theories were testable but now it seems that perhaps they are.
We may look back in a few years and think its amusing that we used to think that our universe was all there was. Its very much like the initial assumption that our country was the center of everything, then our planet, then our solar system, then our galaxy. All of those ideas were wrong. Now it seems that even our universe isn’t special either!