Question

Special relativity

Looking through some super telescope, you see a kid living on Jupiter blowing out 10 birthday candles on his cake. Assuming people everywhere have the same birthday traditions we do,

a) How old is the kid when you are looking at him?

b) The kid is not on Jupiter, but suppose you know the kid is 11 years old when you are looking at him. How far away is he?

Answer 1

Hey there!

For you to understand this concept, you should know the speed of light . The speed of light is mind boggling 300,000 km in a second!!!!

Here light can be from any radiations to anything that you see. So if any instant takes place , it would take some time to reach you. In the case of sound it is slow, when compared to light. Because light is so fast , in a speed that we can't live imagine fully off!

Let me explain one more simple concept also. One light minute is the distance travelled by light in a minute. We already saw that light travels 300,000 km in a second. So in one minute , the light travels 300,000 x 60 seconds = 18,000,000 km = 18 million km. (This distance is one light minute) In the same way when it come to one light year, you could calculate like the same. 300,000 km x 365 days x 24 hours x 60 seconds (dsitance light can travel in a second x seconds in a year)

a) Lets get into the question now. First we should know how many light minutes is Jupiter far from Earth. Jupiter is actually 588 million km far from Earth. This means

(588 million km / 18 million km) = 32.7 light minutes!

This means if you turn on a torch from earth, it would take 32.7 minutes for that torch light rays to reach Jupiter!

In the same way if you saw that kid from Jupiter through that fancy telescope blowing a candle , that just happened 32.7 minutes before our time line at the present!! So he is 10 years and 32.7 minutes old when you saw him blowing the candle.

b) Now comes the concept of light year. If you saw him blowing the 10 year old candle through that telescope , but you knoe that he is 11 years old already, that means that light from that planet took 1 year to reach earth. This means that place is one light year away! Now you know what one light year means! THAT IS A HUMONGOUS DISTANCE!!