Not Scientific Science
Created | Updated Dec 2, 2004
Time travel: sci-fi?
When you look at the clear night sky, you see stars - those tiny
diamonds suspended in the vast pitch-black emptiness. But stars shine
because...? Our own sun, which is a star, emits light. Stars are like
giant bulbs but are much more powerful.
Light travels at a speed of 3.0*108m/s in vacuum and space is mostly
vacuum. In other words light can cover a mighty distance of 300,000,000m in only 1 second!
The thing is that 300,000,000m is a just one of those small amounts in space. Other stars are billions of kilometres - let alone metres - away. Astronomers, in fact, use light year as the unit for distance. One light year is the distance travelled by light (in vacuum) during one
year. Therefore one light year equals (300,000,000*3600*24*365)m.
A single light year is definitely huge: 9.46 trillion kilometres - no
need to put this in digit form - in fact. But where exactly do I want
to converge? A star that you see in the night sky is not one but many
light years away. This means that it is very far away. But most
importantly, it means that light from this particular star takes many
years - and not mere seconds - to reach your eyes! So what?
When you watch a star, you are actually only seeing the light it
emitted years ago. At present, the star may be somewhere else in the
night sky. (Stars do move in space). It might have deflected a
little to the east or north or north-northeast. The star is still
emitting light though. This light will, however, be seen in the
following decades or even centuries; or simply next year.
When you watch stars at night, you are actually looking in the past. So who or what is time travelling? The star? You? Or light? The
further something is from you, the further in the past you are
penetrating into.
Maybe then, someday, the newest technologies will be able to observe
these seconds after the Big Bang - if it ever occurred in the first
place.
Happy Birthday The h2g2 Post!
Other science issues (not too complicated don't you worry)
can be found at the World-Science.net
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