Relativity: unwrapping a mystery
A close look at the foundations of a theory that redefined the universe.
[Posts are sequential, to be read/heard in date order - opposite to the order they’re generally displayed in. Paid-for posts have technical content.]
To hear an audio version of this post (10 mins 40 secs), click the arrow below:
Relativity has proved to be one of the most successful theories of all time. Over the past 117 years or so it’s been credited with explaining a whole variety of phenomena for which no other explanations had been found.
But what explains Relativity?
This isn’t a frivolous or trivial question. For as long as there have been scientists – and before them ‘natural philosophers’ – it’s been the role of science to uncover the causes behind all forms of observed effects. From discovering why the sun rises in the East every morning to why the tides rise and fall across the oceans, from what creates the light and heat pouring out of our sun and every other star to how various life-forms use that light and heat to give themselves energy, every answer leads to yet more questions. Every “This is how it happens” leads to “But how does that happen?”. Science never stops asking “Why?” or “How?”.
Except in the case of Relativity.
Relativity tells us that: (a) The speed of light is a universal absolute; and (b) Every fundamental physical law (including the speed of light) operates identically in every (uniform non-gravitational) state of motion.
All the verifiable evidence to date suggests that the universe does indeed conform with these principles; but there are quite a few un-verifiable bizarre effects that the accepted view of Relativity brings with it. Such as: railway carriages (and other objects) which are simultaneously two or more different lengths, depending on who’s doing the measuring; pairs of clocks that are each simultaneously running slower than the other; pairs of events, A and B, such that A happens before B, both happen simultaneously, and B happens before A (all for the same pair of events) – depending on the state of motion of the observer.
According to the accepted interpretation of Relativity, these aren’t just matters of perception; two clocks are both slower than each other, the same pair of events does actually happen in three different orderings, the same railway carriage is two different lengths at the same time.
Relativity has brought us outstanding successes, from nuclear power to deep space exploration out to the very edges of our solar system. The next logical step would surely be to find an explanation for that unique property of light and its various apparently contradictory side-effects. Who knows what potential benefits this might bring? Or what new perspectives it might reveal?
But the accepted view on Relativity offers no such explanation. That view simply says “That’s just how it is. We live in a relativistic universe. Get used to it.”
For science, which is all about finding explanations for things, this seems like a big oversight, particularly in respect of a theory with such far-reaching implications. Because Relativity is not without its down side: it rules out – for ever – anything or anyone crossing space at faster than the speed of light (so forget about interstellar travel at realistic time-scales); it issues dire threats of potentially catastrophic time-slips if anyone is ever clever, and foolish, enough to find a way around that speed barrier; it places serious obstacles in the way of any scientific explanation of universal effects that are required to perform identically over all states of motion – notably inertia and gravitation.
In short: in accepting the standard view of Relativity without requiring any notion of why it behaves the way it does, scientists are effectively agreeing to having their hands tied in respect of various possibly highly important areas of research – without even asking why.
===============================================
So why have five generations of scientists found Einstein’s theory so persuasive, even with all those unexplained and unproven weird side effects? Sure, the observations fit the formulae, for those situations that can be tested - but that could be for quite a different reason from the one Einstein came up with (watch this space…). Maybe we should go back and look again at the evidence he himself found so convincing.
At the time of Einstein’s deliberations various puzzling finding were being talked about, but his mind was made up by just two. In his own words, “They were enough”. The two observations that he found so compelling were Fizeau’s experiment and the aberration of starlight. Both deserve closer examination. We’ll look at the starlight issue in a future post; for the time being Fizeau’s experiment will give us plenty to think about.
In 1851 Hippolyte Fizeau was grappling with a conundrum that had the scientific world baffled. Light slows down when passing through water, right? (Or any other translucent medium). If the water is flowing in the same direction as the light, that helps the light speed up a bit - but it doesn’t add its full speed to the speed of the light passing through it.
No, the speed of light in moving water is less than the speed of the water plus the speed of light in static water. Why would that be? Shouldn’t the water boost the speed of the light, carrying it along with the full speed of its own momentum?
Fifty years later Albert Einstein was looking at the formula that Fizeau had derived for this situation. It was remarkably similar to a formula of his own - which was nothing to do with light in water. His concern was men in railway carriages.
If a man is walking along inside a railway carriage at speed u, and that carriage is itself moving at speed v, then from the perspective of an observer standing on the railway embankment that man’s resulting speed will be u + v. Obvious, innit?
Not to Einstein. When he applied his Relativity theory to the man in the train, from the perspective of the trackside observer that man’s overall speed turned out to be a little less than the sum of u and v; Relativity tells us that we can’t simply add two speeds together like that - and at speeds near to the speed of light that difference can be significant.
Einstein derived a formula giving the combined speed. And when he applied his formula to the light-through-water situation it fitted to a high degree of accuracy. Einstein reasoned that the light-in-water speed was being added to the water’s own speed, just like the man’s speed and the carriage speed - but just like the man on the train, a Relativistic adjustment was needed for the overall speed.
Einstein took this as totally convincing confirmation of his Relativistic velocity addition formula - and so also of his Special Theory of Relativity. Not to put too fine a point on it, this is the bedrock on which Relativity is founded.
Fast forward now several decades, to a rather better understanding of how light moves through water. We’ve now known for some time that light is impeded by water, not swept along by it (like the man in the train), slowed by the interaction of the light with the atoms in the water itself (see the video at the end of this article for details).
It’s not a great leap to realise that less frequent interactions, when the atoms of the water are moving away from the light source, will give less of a slowing effect; even a simple analysis yields the result that the resulting light speed is not increased by the speed of the water - the issue that so puzzled Fizeau and his colleagues. Just from this observation it’s immediately apparent that the ‘light moving through water’ scenario is radically different from the ‘man through train’ scenario.
So, contrary to what Einstein himself believed and considered so significant, we don’t need Relativity to explain this effect. Detailed analysis yields a formula which is remarkably similar to Einstein’s, without reference to Relativity, giving results identical to Einstein’s to ten-figure accuracy or better.
You can see that analysis, and that formula, in this post. The take-home message is this: one of the two cornerstones to Einstein’s formulation of Relativity theory - causation of ‘the Fizeau Effect’ - is itself totally without foundation. [Surprisingly, this isn’t mentioned in articles on Fizeau’s experiment and its place in the derivation of Relativity Theory, even though it’s now common knowledge.]
In future articles we’ll look at how other misperceptions have shaped Relativity and how it’s interpreted. We’ll confirm all that’s best in it and jettison those myths that have stood in the way of scientific endeavour for over a century. In the meantime check out the articles, presentations and other resources available here.
This video from Fermilab, the US National Accelerator Laboratory, comparable to the Large Hadron Collider, gives details on the motion of light through water: