Tag Archive: paradox


    This post is (partly) an answer to the puzzle that I posted here (Why’s the sky dark at night?).                                                                                                            Did I say partly? The reason is that this “paradox”(The Olber’s Paradox as it is [in]famously known) has yet to be completely answered.

 According to Henrich Olber, the   sky should look something like the image that I found on Wikipedia(and found particularly apt for this post). But that’s not the case, right? Several explanations have been proposed for this somewhat ‘strangeness.’

Theory 1: Dust present between the stars and the galaxies veils the light that we should be seeing.

What’s wrong with it? The dust from the stars would eventually heat up and start radiating the light.(that’s one theory that eats the “dust”)

Add-fact: Even if all the matter in the Universe were converted to Energy(the famous e=mc^2), given the immensity of the Uni., the   energy would be just enough to raise the temperature of the Uni. to 20 kelvin(that’s about -253 deg.Celcius- not very much, huh!)

Theory 2: Let’s bring some “Big-Bang” to this paradox. Galaxies are dispersing, always running(or flying) away from each other(that’s the Big-Bang Theory!). So, a phenomenon known as the redshift occurs. As a sidenote, redshift is the same phenomenon that occurs  when the pitch of a siren increases when it approaches you and lessens as it moves away(here’s an audio). The main difference here is that it’s light. As another sidenote, light consists of a spectrum, there is the visible region(made up of the colors), there is the microwave region(the name says it all), the radio region and a host of other. The difference is the frequency with which vibration occurs. Returning to our paradox now.

So, according to the theory, the visible part gets shifted to the invisible infrared part(are you still with me?) and that’s why we do not see the light(literally).

Something’s wrong, again!! : The problem with this explanation is that if there is a shift in the visible region, then, there should also a shift from the other Ultraviolet region to the Visible one and we are (again) at square one.

What, another theory(3)?: Yep. This one’s a little tricky. The dark sky is due to the large distance light has to travel to reach us. It is, more scientifically speaking, attenuated as it reaches us.

Triple Trouble:Let’s take a concentric layer on which stars are uniformly spaced. If we decrease the distance from the centre, the ellipse formed will be shorter and thus, there will be lesser stars on this one. Now, we would be right if we said that the light from the distant stars gets attenuated by a certain factor f when it reaches the other stars. However there is a factor f  more stars on the larger ellipse. The net effect is a cancellation!

What’s Generally Accepted: Today’s most apt explanation is “The Universe NOT being infinitely old although infinitely large”. Light has a finite velocity(~300000 kpsecond) and light from the distant galaxies takes some time to reach us. For e.g light from the sun takes about 8 minutes to reach the Earth, so we’re seeing the sun as it was 8 min. ago. As it stands, our Universe is approx. 13 billion years old. So, we cannot see light beyond that! Galaxies, on the other hand, do not live infinitely, their emitted light dim. These two conditions prevent a fully blazing night sky to be seen.

The Trouble: Just Jokin’, I leave it to you to find it and possibly gain International fame!

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“He who is fixed to a star does not change his mind.” -Leonardo da Vinci

                        Whenever he is alone at night, Henrich likes to watch the beautiful stars in the sky. It so happened that, one day, as Henrich was sitting at his usual spot, a seemingly innocuous thought flashes across his mind- “why is the sky dark at night?”- he asks. Being rather proficient with Science, Henrich is able to determine that if the Universe is uniformly filled with stars, the whole of the night sky should be blazing with lights from these stars, but that isn’t the case. “Why?”, he asks. Why, indeed?

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The answer to this question is perhaps one of the most famous paradoxes known in science!

You cannot teach a man anything; you can only help him discover it in himself.” -Galileo

Here’s the answer!