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It’s pretty clear that light holds the key to the whole matter of Relativity – and also, arguably, to the whole matter of matter itself. It’s not at all clear why light should travel at the same speed relative to any other object – but it becomes crystal clear why it should seem that way, when we start looking at the fine detail.
First let’s take a look at that notion that light travels at the same speed relative to anything else. How about a simple analogy: You’re driving at 40 miles an hour along the motorway, a police car passes you moving at 100 miles an hour – and it pulls away from you at a relative speed of one hundred miles an hour, not just sixty. So ok, you speed up to ninety miles an hour, trying to keep up with it – and it’s still pulling away from you at a hundred miles an hour relative to your speed, not ten! And here’s maybe the strangest thing of all: the police car hasn’t changed its speed, hasn’t accelerated at any time; it’s just doing that steady one hundred miles an hour all through that car-chase drama.
This is exactly what’s proposed by Relativity, for light, though at a rather faster speed than 100 miles an hour. Never mind if you’re moving at 30 miles an hour, 90 miles an hour, 1,000 miles an hour or a million miles an hour, light will pass you and pull away from you at exactly the same relative speed: 299,792,458 metres per second.
Here’s where you’re surely bound to start thinking: “This isn’t about the light, that’s not changing in any way. It’s got to be about me, the moving observer, and how I perceive or experience the speed of this light that’s passing me.”
And you’d be right. But how? And why? And how come this applies not just to people, physical observers, but to any form of matter – everything acts as if light is passing it or interacting with it at that same relative speed, no matter what speed the object in question is itself travelling at?
There’s a remarkably simple answer to this, one which makes it absolutely clear why everything is the way it is, on closer examination. The answer is, quite simply: everything is made of light.
Yes, you read that right. Every physical object, every particle, in the universe is formed from light (including those higher and lower frequencies that our eyes just don’t see). We’re used to having light flying all around us, and across space between the stars, at that roughly 300 million meters a second. But in extreme circumstances nearly 14 billion years ago – just after the Big Bang – untold gadzillions of photons of light were packed into an incredibly tiny space. And in that jam-packed space – smaller than a single subatomic particle, we’re told – some of those photons, one in a few billion or so, wrapped around on themselves and formed stable loops cycling on the spot at the speed of light. We call these stable loops ‘elementary particles’, and as the universe expanded and cooled those elementary particles grouped together to form atoms – and the rest is history.
This isn’t just a flight of fancy, or idle speculation. There are reams of scientific studies that support this idea, including quite a few from Nobel laureates. In 1925 Count Louis de Broglie was the first person ever to win a Nobel prize on the strength of his PhD thesis, in which he proposed that electrons were wavelike in nature. Just two years later Clint Davisson made another Nobel-winning discovery, when he and his grad student showed interference patterns – a sure sign of wave-based structure – from streams of electrons reflected off crystals of nickel. At least ten studies since then, probably quite a few more by now, have shown photons and elementary particles are interchangeable in particle accelerator experiments.
In 1934 two eminent physicists, Breit and Wheeler, proposed a process in which two opposing high-energy photons would be collided head-on to produce a pair of particles, one of matter and the other of antimatter (Think of two fast-moving ice-skaters meeting head-on and linking hands so they end up spinning on the spot together, then releasing each other’s’ hands: two linear motions become two spinning motions). A multi-stage version of the Breit-Wheeler Process was achieved in 1997 at SLAC, the US National Accelerator Lab at Stanford University, creating particles of matter from pure light. So real substance was given to the timeless words of sages and mystics throughout the ages: matter is indeed formed from light.
Just to put a bit of icing on the cake and bring the story full circle: in 2008 a team of French physicists, Catillon, Gouanère et al., actually recorded physical evidence of the ‘particle internal clock’ first proposed by de Broglie almost a century before, the periodic cycling of the wave that forms the particle we refer to as an electron. Erwin Schrödinger (of Schrödinger’s cat fame, and more significantly the quantum mechanical wave equation that won him his Nobel prize) had in 1930 theorised a periodic ‘jittery motion’ in the behaviour of an electron which suggested a regular cyclic pattern in its formation; the French team actually found that pattern in particle accelerator experiments and recorded it in graphs. Something is zipping around inside an electron – at the speed of light!
All of this, of course, goes to confirm Einstein’s proposal that matter is energy: E = mc squared (as if we need any further confirmation, on top of atom bombs and nuclear power). That energy is light energy, photons spun into tiny loops circling at almost 300 thousand kilometres a second.
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So why might this cause the speed of light to be experienced identically relative to every other observer or object, whatever their own state of motion?
For the answer to this we need to look closely at the implications of that light-based structure. Light travels at the speed of 300 million metres a second, usually abbreviated to the letter c. In a static particle all of that speed is taken up with cycling round on the spot to form the particle itself. But if that particle is moving, then this means the light-flow forming that particle is travelling along in the direction of the particle’s motion at the same time as cycling around to form the particle.
In effect, that light-flow will trace out a spiral path: think of an airplane putting out a trail of orange smoke, say, behind it – skywriting. Let’s say it’s flying at sixty miles an hour – a mile a minute – just to keep things easy. If it flies repeatedly in vertical circles, each a mile around, in the same place, it’ll trace out sixty circles an hour; that’s pretty obvious.
If the pilot decides to travel cross-country while still tracing out those circles, though, things change. That trail of orange smoke becomes a spiral – and if the pilot keeps the diameter of the circles the same, there won’t be so many circles per hour as some of the plane’s speed is taken up with the cross-country element of its motion.
We can pin down that effect more precisely by considering a length of cord wrapped around a long straight pipe. Again keeping figures simple, let’s say the cord is 80 centimetres long and the pipe is eight centimetres around. This means if we wrap the cord around the pipe with the turns tightly bunched together, we’ll get exactly ten turns:
But if we stretch the cord out along the pipe at the same time as wrapping it around, we’ll get less turns out of our length of cord. We may get only nine, or eight, or even less – it depends how far along the pipe they go. If we took a photo of this arrangement, each half-turn would show as a diagonal rather than a vertical line (assuming our pipe is horizontal).
The same principle would apply for our skywriter – and for our light-flow for a moving particle (on a much smaller scale). Let’s look at how the figures work out in a very simple example with our cord-around-pipe scenario. To make it even clearer, we could hammer our pipe flat; the distance along the pipe, the distance around the pipe and the length of the cord itself (for one half-turn) would form the sides of a right-angled triangle.
If we think of wrapping the turns of cord spirally 6 centimetres apart, that’s 3 centimetres along the pipe for each half-turn; each of those half-turns would also measure 4 centimetres around the pipe. This gives a right-angled triangle with shorter sides 3 cm and 4 cm. If you’re familiar with right-angled triangles you’ll know that this makes the diagonal (the length of cord used in each half-turn) 5 centimetres, since 3 squared plus 4 squared equals 5 squared. So each whole turn of the pipe takes ten centimetres, giving us only eight turns for the complete cord rather than ten. If we spaced the turns further apart, we’d get even less turns out of our eighty centimetres of cord.
Exactly the same goes for our light-flow around a particle. The light-flow through space (with the motion of the particle) and the light-flow around the particle combine as two sides of a right-angled triangle to give the full rate of light-flow (which we call c, remember). So if the speed of our particle through space is three-fifths of c then the rate of energy-flow around the particle will be four-fifths of c, giving five-fifths of c, or full light speed
Unwrapping all this, we see that a particle moving at three-fifths of light speed will only have four-fifths of the full rate of light speed going around it to give it its form. And here’s the kicker: the energy flow going around a particle (as well as between particles) is what carries time effects *. It must be – there is nothing else! So an object moving at three-fifths light speed will experience time at only four-fifths of the normal rate. This is precisely the time dilation factor given by Relativity theory for such a situation.
More generally, the linear component of the formative energy-flow in an object moving at any speed will reduce its cyclic energy-flow component, and so its time-experience, by exactly the factor defined by Relativity as some sort of unexplained cosmic effect. This is the factor that’s been shown to apply to the extended half-life of ultra-high-velocity muons arriving on earth from the upper atmosphere – the internal clocks of those muons have literally slowed down, extending their effective lifetimes, due to their reduced time-experience resulting from their reduced cyclic energy-flows.
This isn’t by any means the whole story as to why everything experiences the speed of light relative to them as full light speed – but it’s a good start. A reduced clock speed goes a long way to balancing a reduced relative light speed to give a false impression of full speed. In the next post we’ll see how other aspects of this distorted perception, due to the motion of an observer or physical object, complete the picture to give the impression of total symmetry between different states of motion – including apparent invariance of the relative speed of light.
* Footnote: The fact that the passage of time is the result of the energy-flows around and between particles is implicit in Relativity Theory (though not recognised there):
(a) In Relativity formulae and equations, the time component is always multiplied by c, the speed of light; this is a natural consequence of time-effects being caused by those energy-flows – at the speed of light;
(b) In Relativity time is seen as an imaginary dimension, represented mathematically by i, the square root of minus one; this reflects (!) the fact that in Relativity objects are regarded as moving through time, whereas time is actually moving through those objects as energy flows – Relativity gives a sort of looking-glass perspective on the true nature of time. [It’s also a fair question to ask why would things (and people) age simply as a result of moving through an imaginary dimension – whereas it makes perfect sense that energy flowing through objects, carrying information on changes of state, etc, would give rise to changes in those objects – what we call ‘ageing’.]
Technical note: The flow-path of light energy around a particle or composite object may be quite complex, it needn’t be just a single circular loop. This explanation of particle or object time dilation still applies in the same way. For those interested in such things (and with a bit of maths ability), the next post, time dilation in complex energy-flow structures, gives a detailed breakdown of such situations. There is a small charge for access to this post. Note that Complex energy-flow structures includes multi-particle objects, such as spacecraft, people etc - this analysis covers such objects, filling in the detail to Ryan Chester’s overview of time dilation in composite structures, referred to in the previous post: Relativity? What Relativity?
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