Schrödinger's Cormorant

2.2 It’s All Relative

Introducing the concept of relativity in classical physics

You are lying on your backs in the Piazza Michelangelo, gazing up as the stars overhead slowly move across the night sky. “Actually”, opines Nefertiti, “it is we who are moving, it just looks like it’s the stars moving because we are so focussed on ourselves as the centre of everything”. “How do you know?” demands Cormorant. “Now that” chimes in Galileo, who has materialised nearby, ”is an interesting question. Let’s discuss it - but keep your voices down, the Inquisition may be about”. Galileo has been here before – he explains that motion is always relative: "there is no such thing as absolute velocity. Everything is static in its own reference frame and moving in other reference frames. This is a central idea of relativity. So, in your frame of reference (that’s the technical term), you are static and the stars are revolving around you but to your distant relative, gazing through his thirteen telescopic eyes at the sky above his planet orbiting Alpha Centauri B, it looks pretty clear that it’s your planet which is moving, while he is comfortably at rest in his acid bath. Both of you are right – it’s just a question of perspective.”

“I knew that” replies Nefertiti.

Later, as you are flying home at the end of your Florentine mini-break, Nefertiti decides to practise her shot-putting in the aisle of the plane (N.B. always check with your airline first). She throws the same distance – measured along the length of the fuselage - that she regularly achieves when she is on the ground at home: the speed of the plane makes no difference.

Cormorant is still sitting in his nest, awaiting your return. Galileo reports Nefertiti's result to him. “This comes as no surprise to me. I established long ago that if you do any kind of mechanical experiment you get the same result in any frame of reference, regardless of movement of those reference frames relative to one another. This is another central idea of relativity. So if you, Signor Cormorane, settled in your nest, could peer into the plane and gauge the distance Nefertiti has achieved, you would agree precisely with her own measurement. If you both measured the time of flight of the shot, you would also agree precisely. Again, the speed of the plane makes no difference.“

Cormorant decides to pass the time by thinking about this mathematically:

Question 2-1

All of this feels like a rather long-winded way of confirming what now – steeped as we are in everyday experience and Newtonian mechanics – seems obvious. It’s important, though, because it helps convince us numerically that what Galileo said is right: the laws of mechanics are the same in any reference frame. So that’s relativity. “OK”, says Cormorant, “that was pretty easy. I think maybe we make too much fuss over this Einstein guy.” Nothing could prepare him for what comes next.

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