What do you mean, “it’s a silly question”? Sir Arthur Eddington wouldn’t agree with you. He argued in 1924 that the mass of the Sun could be expressed in kilometres (1.5 km actually) and that the mass of the Earth was about 5 millimetres (on which scale, the mass of a person would be a length considerably smaller than an atomic nucleus). Continue reading
I have a recurring nightmare – that one day someone will invent a solution to global warming, one that involves either extracting excess carbon dioxide from the atmosphere, or persuading the majority of people to drive electric cars which can be charged from solar power.
“Why is that a nightmare?” I hear you ask. Surely it’s what everyone is desperately hoping and praying for? Well, yes, of course it will save us and the planet from overheating and flooding etc, so of course it would be welcome – but it would then immerse us in another, rather different problem, in that the growth of the car would continue unchecked, and in fact probably accelerate. Continue reading
In my last post on this topic, I explained that there are two distinct ways of expressing the relationship between mass and energy in special relativity. One is known as concomitance, where mass and energy are really the same thing, and different observers moving at a constant speed relative to each other will disagree on the magnitudes of both quantities. The other is the interconvertibility approach: mass and energy can be converted into each other, mass being Lorentz-invariant (all inertial observers agree on its magnitude) while energy is not. In the former view, the equation E = mc2 expresses the identity between the two concepts and can be applied to any macroscopic body, while in the latter it is a conversion formula used to calculate how much energy a given mass can be converted to, and vice versa. Continue reading
This was one of Alexander Pope’s truest adages (as long as you remember that the emphasis is on the word little: there is nothing dangerous in being well-informed, the trouble arises when one extrapolates from an inadequate knowledge base). Unfortunately, in this hyper-specialised world, all any of us can manage on most topics is a little learning; we can specialise in one, or perhaps two or three things, but for the rest we have to just accept what we are taught and what we read in books and newspapers, or hear on TV or radio.
I am frequently reminded of this by examples I come across, in blogs, popular science articles, and even some books, of the misuse of Einstein’s famous equation E = mc2. It seems to me that these are often founded on a very inadequate understanding of the equation, what it means and where it comes from. Continue reading
An evening with some old schoolfriends from the 1960s, and another evening listening to rock classics on Planet Rock, are responsible for this one. It was one of my favourite poems at that time, but I have not read it for years. Continue reading