Universe (3)

The last issue I want to touch on in this essay is time. We are used to thinking about time in terms of the two domains of past and future, separated by a constantly moving “now”. However, as stipulated by Einstein, time is local, not absolute. This means that there is no universal “now” across the Universe. Light takes 8 minutes to travel from Sun to Earth. If I asked you whether the Sun is still there “now” we would have to first agree on which “now” I am talking about. If the Sun disappeared “now” (Earth time) we would not find out about it for another 8 minutes. There is no “now” instantly applicable to both the Sun and Earth. In fact, there is no such thing as simultaneous events. Using similar logic we will realise that looking into the night sky we see stars the way they were thousands, millions or even billions years ago. It is like looking back in time (with the Earth used as reference).

OK – let’s assume that the Sun went out 4 minutes ago. This event cannot be undone and darkness will embrace the Earth in another 4 minutes. So what is the status of the Sun’s disappearance in terms of Earth’s chronology? Has it happened? Not really, because we have no way of knowing about it at this moment and it has not affected us in any way. So it has not happened? Again, not quite because future is normally something we can affect, which does not apply in this case – the darkness will inevitably fall in 4 minutes. The cosmologically correct explanation is that Sun’s disappearance is outside our space-time cone i.e. outside the area of space-time which either has affected us or can be affected by us. There is even a clever term for this in-between state – “elsewhen”. In this sense much of the future has already happened but has not arrived to us yet.

One last comment. What is the Universe expanding into? Apparently this question cannot be answered because it is the space itself that is expanding. Let’s imagine a two-dimensional world on the surface of a balloon which is being inflated. In the two-dimensional convention it is not expanding into anything – it just keeps getting bigger. Our Universe does the same in 3D + time. Think of Neo trying to get out of the subway station where defunct programs were parked.



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