Relativity for dummies. Part 1 – How fast?

How fast?

How long does it take the light to get from the Sun to the Earth?

A:  No time all.  You will hear the answer ‘8 and a half minutes’ but that is from our perspective.  From the perspective of the light, it takes no time at all!  So it takes the light no time, be we see it as taking over 8 minutes.

The point is that time itself is relative. Time changes with speed, it is just that you have to be travelling at incredible speed to notice.  The light in the above example, is actually travelling at infinite speed.  But relativity means time distorts and we observe the light travelling at the fastest speed anything will appear to be travelling at, the speed of light.

Yes, you can go faster than 300,000km/s (lightspeed), it just doesn’t look that way to others.

You may read that the approximately 300,000km/s (the speed of light) is the fastest speed there is. In reality this depends on point of view).  You will also read that if you travel fast enough time will pass more slowly and if you travel the over 4 light years to the nearest star fast enough that although it will still take over 4 years only 1 year will pass for you.  So you would then have travelled over 4 light years in 1 year of your time. If you divide distance travelled by time you get 4 light years per year- or 4x the speed of light at 1,200,000km/s.  The traps that for someone who stayed back on earth over 4 years will have passed so they will see you as having only slightly below the speed of light.

But for you, it is possible to start accelerating and just keep on accelerating with everything appearing normal and able to keep accelerating to 1 times speed of light, 2 times, 4 times and even faster.  It is those that do not come for the ride who will see of as just getting closer and closer to the speed of light but never reaching that speed.


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