The answer is 42

Douglas Adams' Hitchhiker's Guide to the Galaxy, a tetralogy in five volumes, is something of a cult among scientists and technorati, for being loaded with mind-boggling fictional science, and also deliriously funny.
According to The Hitchhiker’s Guide to the Galaxy, researchers from a pan-dimensional, hyper-intelligent race of beings constructed the second greatest computer in all of time and space, Deep Thought, to calculate the Ultimate Answer to the Great Question of Life, the Universe, and Everything.
After seven and a half million years of pondering the question, Deep Thought provides the answer: “forty-two.”
The reaction: “Forty-two!”
“Is that all you’ve got to show for seven and a half million years’ work?”
“I checked it very thoroughly, it’s 42,” said the computer, “and that quite definitely is the answer. I think the problem, to be quite honest with you, is that you’ve never actually known what the question is.”

That's why lots of astrophysicists know that the answer is 42, and they've been putting some effort into finding the question; here are two serious attempts:

"The preliminary results of a new measurement of the so-called Hubble Constant, taken by radio telescopic means at Cambridge University in England is 42. The Hubble Constant determines the speed at which galaxies are receding from each other, and thus tells us the age of the universe from the time of the Big Bang. It so happens that Douglas Adams, in the book and radio series A Hitchhiker's Guide to the Galaxy in 1978 had a massive computer calculate the meaning of life and the answer was: 42." (8 novembre 1996).

"After pondering the weighty question of the mass of the Milky Way galaxy, astronomers have come up with an answer: 42.
That is, our galaxy weighs three times 10 to the power of 42 kilograms - a number written as 3 followed by 42 zeroes, which has echoes of author Douglas Adams's fictional answer to the question of life, the universe and everything in his series Hitchhiker's Guide to the Galaxy.
It seems esoteric but knowing the weight of the galaxy - the amount of matter it contains - is key to solving important astronomical problems. "(Australian Sunday Telegraph - 6 juillet 2007)

The Hubble Constant is a pretty good candidate for the Ultimate Question, because it is supposed to determine the velocity of expansion of the universe, and by that way to tell us if our universe is for ever expanding, or if it will slow down, stop, then go into reverse toward the Big Crunch. Alas, even though our eminent scientists don't really have a clue, it seams that more recently the Hubble Constant's value is estimated more often as around 65...

Was Deep Thought sadly mistaken ?
Could it be that the answer is really 65 ?
Horresco referens...

Mise à jour 21 mars 2013 : We also have a new estimate for how fast the universe is expanding (a.k.a. Hubble’s constant): 67.15 plus or minus 1.2 kilometers/second/megaparsec. (One megaparsec = around 3 million light years). That is a slightly less expansion rate than those derived from previous data collected by NASA’s Spitzer and Hubble space telescopes, which employ different measurement techniques.
http://blogs.scientificamerican.com/cocktail-party-physics/2013/03/21/walking-the-planck-our-lopsided-universe/