Stranger Than We Can Imagine Read Online Free Page B

last-ditch and somewhat extreme attempt to locate a fixed point, could we not declare the centre of the universe to be our omphalos? The answer, once more, is no. There is no ‘centre of the universe’, as we will see later, but for now we can also reject the idea for being ridiculously impractical.
    So how can we say anything definite about our position, or that of the cup of tea? There may not be a real ‘fixed point’ which we can use, but we are still free to project our own frames of reference wherever we like. We can create a reference frame centred on ourselves, for example, which allows us to say that the tea is moving relative to us. Or we can create one centred on the tea, which would mean that we were moving relative to the cup. What we can’t do is say that one of these frames of reference is correct or more valid than the other. To say that the tea moved past us would be to declare our innate, tea-ist prejudice.
    There is an apt example of how one frame of reference is no more valid than another in Einstein’s 1917 book,
Relativity
. In the original German-language edition, he used Potsdamer Platz in Berlin as the frame of reference in one example. When the book was translated into English, this was changed to Trafalgar Square in London. Bythe time the book was out of copyright and made available online as an eBook, this had been changed to Times Square in New York because, in the opinion of the editor, ‘this is the most well known/identifiable location to English speakers in the present day.’ What is important about the reference point, in other words, is that it has been defined as the reference point. Practically, it could be anywhere.
    The first step towards understanding relativity, then, is to accept this: a statement of position is only meaningful when it has been defined along with its frame of reference. We can choose whatever frame of reference we like, but we can’t say that it has more validity than any other.
    With that in mind, let us return to Zurich in 1914.
    Einstein gets on a steam train in Zurich and travels to Berlin. He is leaving his wife Marić and their two surviving children in order to begin a new life with his cousin, who will later become his second wife. Imagine that the train travels in a straight line at a constant speed of 100 km/h, and that at one point he stands, holds a sausage at head height, and drops it on the floor.
    This raises two questions: how far does the sausage fall, and why is he leaving his wife? Of these two questions Einstein would have found the first one to be the most interesting, so this is what we will focus on.
    Let us say he holds the sausage up to a height of five feet above the train floor and drops it. It lands, as you would expect, near to his scuffed shoes, directly below his raised hand. We can say that it has fallen five feet exactly. As we have just seen, such a statement only makes sense when the frame of reference is defined. Here we take Einstein’s frame of reference, that of the inside of the train carriage, and we can say that relative to that, the sausage fell five feet.
    What other frames of reference could we use? Imagine there is a mouse on the railway track, and that the train rumbles safely over the mouse as Einstein drops his sausage. How far would the sausage fall if we use this mouse as a point of reference?
    The sausage still starts in Einstein’s hand and lands by his feet. But, as far as the mouse is concerned, Einstein and the sausage are also moving over him during the sausage’s fall. During the period between Einstein letting go of the sausage and it hitting the floor, it will have moved a certain distance along the track. The position of his feet when the sausage lands is further down the track than the position of the hand at the moment it was dropped. The sausage has still fallen five feet downwards, relative to the mouse, but it has also travelled a certain distance in the direction the train is travelling in.