The farther away you look, the further in the past you see
The Sunday Nation
Nairobi,
22 June 2014
When Albert Einstein discovered the principle of relativity, he was wondering about the relationship between cause and effect. The question in his mind was: can something happened and its effect be observed instantaneously with the occurrence? The obvious answer was no; there must be some time lapse from the moment an event occurs to when the observation is made.
Think about it; when you open to this page in the newspaper, some time must pass by before you are able to see it. It is a very short time lapse, but certainly not zero.
This led Einstein to next logical conclusion: that there must be a minimum time between cause and effect. Furthermore, if there is a minimum time, it follows that there is a maximum speed of interaction.
When this dawned on him, Einstein went on to proclaim that light must be travelling at this maximum speed of interaction. Without going into the detailed reasoning behind this proclamation, it is enough to state that, to date, no other phenomenon has ever been found to travel faster than light.
By using an ingenious definition of the unit for measuring distance – the metre – scientists fixed the speed of light to an exact value: 299,792,458 metres per second exactly! But for most purposes, this figure is rounded off to 300,000,000m/s; or 300,000km/s.
Now if you have normal eyesight, you will be holding this page about 30cm away from your face. Therefore, moving at 300,000,000m/s, the light from the page takes about 0.000000001 of a second to reach your eyes. That is; one billionth of a second!
So, you are not seeing the page as it is now but how it was one billionth of a second ago. We can extend this argument and say that everything you see with your eyes is what was there at least 0.000000001 of a second ago.
Furthermore, the farther away you look, the further into the past you see. For example; the moon is about 384,000km away, so light from there takes about 1.28s to reach the earth. We see it as it was about one and a third second ago. And at 150,000,000km away, light from the sun take 8m:20s to get here. If God switched it off, we wouldn't notice anything for more than 8 minutes!
Now the nearest star to the sun is 39,900,000,000,000km away. Light from there takes about 4 years and three months to get here! Since this is the nearest one, it means that when we look up in the sky at night what we see is stars as they were at least 4 years and three months ago – the view you'll see tonight was how things were BEFORE March 2010!
But we can take it further: if we looked at stars that are far enough, shouldn't we be able to see the time when the universe began?
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