Theory of relativity…

On my break, I had a chance to read, or at least get half way through, a book called “The Elegant Universe”, by… er… someone.

Its about superstring theory, which is the current grand unified theory, which attempts to unify Einsteins relativity with quantum mechanics. Its all quite interesting, and complicated.

But… Ive always struggled to get a feel for the theory of relativity. This book had a nice explanation which I will attempt to describe in a kinda simplified way… I will try and get it right, let me know if I make any mistakes!

1. You have to believe the speed of light is constant. This is hard to do, because it means if someone throws a ball at you at 10kmh and you run towards the ball and 10kmh, then the ball will hit you at 20kmh. This doesnt happen with light. Light will always be heading towards you at the speed of light, or away from you at the speed of light, regardless of how fast you are heading towards or away from the source. This has evidently been experimentally proven since ages ago. But this is the key point.

2. Imagine a atomic clock, where a photon bounces back and forth between two plates. Bounce, bounce, bounce. At the speed of light. The number of bounces are like the ticks of a clock.

3. Now, if the clock is not moving, it just goes, bounce up, bounce down, bounce up, bounce down at the speed of light. Isnt bounce a funny word…?

4. But, imagine if someone puts it in a bus. And the bus is moving, and you are just watching from the footpath. What do you see? Bounce up, bounce down, sure… but because the bus is moving, the photon appears to move in a sine wave kinda thing. So far so good right?

5. So, from your point of view, the photon is travelling a longer distance, over the sine wave thing. Now, we know that Distance=Speed*Time right? Distance has just increased, so either speed or time must increase too. But… from point 1, speed is constant. So…. time increases. ie, time slows down for the clock. Similar things can be shown for length and mass.

and this has been experimentally established. What a weird world we live in!

Theory of relativity…

3 thoughts on “Theory of relativity…

  1. Falafulu Fisi says:

    Yes, relativity and also quantum mechanics , the two pillars of modern physics are weird, in terms of everyday experience. I did papers both in quantum mechanics & relativistic mechanics when I was at Uni, and when the concepts were first introduced, they seemed unreal, because they had nothing equivalent in our everyday experience.

    Such concept in relativity that the faster you travel towards the traffic lights, if it is red lights it would turn greens, because of the Doppler Effect. The faster you travel away (or recede) from the traffic lights if it is green lights, it would turn red (red-shift). Red-shift is the measurement that is used today to detect how fast are other galactic bodies are moving away from earth. So, relativity is weird if one thinks of it in terms of everyday experience. Say if you have 2 photons, which they both travel at speed of light , C, traveling in opposite direction, either photon will see each other receding at speed of light C and not 2*C as we see in everyday experience. Time could be delayed (slowed down or speeding up) and length could be shortened (contract) or lengthen (expand).

    Another concept is quantum mechanics (QM), is that the outcome of any measurement (experimental observation) is dependent on the observer (experimenter). It basically says, that things are not real unless one looks. An example here, is that the moon doesn’t exist, unless one looks up the sky. So, if one doesn’t look up to the sky to observe the moon, one could argue that the moon doesn’t exist simply because you haven’t look (ie, measure or perform experiment). This school of thought is known as Copenhagen Interpretation.

    After all, that is how physical reality manifest ifself. So, Relativity and Quantum Mechanics are just how Physics (Laws of the universe) work. There is no contradiction there at all.

  2. Great example with the photons going away from each other! Thanks! but doesnt quantum mechanics also say that to observe something also interferes with the thing being observed? so you are no longer observing what you are trying to observe in the first place? Its very weird, but fascinating. The book is great, but I kinda gave up with the multidimesional calabri yau stuff…

  3. Falafulu Fisi says:

    Greg said…
    but doesnt quantum mechanics also say that to observe something also interferes with the thing being observed? so you are no longer observing what you are trying to observe in the first place?

    Yes, that is correct. The philosophy of quantum mechanics (QM) has been debated for almost a hundred years to date, started by proponents Neils Bohr and his Copenhagen fellow scientists (Max Born, Heisenberg) against Einstein, Schrodinger and others where they thought at the time that QM was incomplete. To Date the debate is still going on. Facts are facts , ie, QM experimental observations are verified and solid, the disputes are in its interpretation. Bohr on one side said that when you make observation (the very act of doing that changes the outcome), which philosophically mean that reality is subjective and not real objective. Einstein’s camp on the other hand, that QM is in complete, since reality must exist with or without an observer to change the outcome. He mean that reality must act and operate independently without a conscious mind (an intelligent observer). The debate has gone far from Physics into philosophy and Epistemology. The definition of reality and existence in philosophy, that things (material) must exist in one entity for all time (eternity). Any entity that doesn’t conform to this, then it is not real (doesn’t exist). But QM says, that matter exist in dual nature, ie, Particle-Wave-Duality. This means that matter could exist in one entity (particle) and at a certain point in time it becomes different or changes into another entity (wave). Einstein didn’t like this intpretation because it makes reality & existence becomes subjective rather than objective where declared at the time that QM must be an incomplete theory.

    The whole epitome of this QM debate is symbolized by the well-known double-slit experiment. Watch it here on an animation YouTube clip:

    Dr Quantum – Double Slit Experiment

    Greg, would you mind sending me an email please, since I couldn’t find your contact info in your blog. I have some software ideas that I want to discuss with you in an informal sense. Who knows, ideas might lead to something.


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