COSMIC EXPANSION:GRAVITY SAVES
Your waistline maybe spreading but you can’t blame it on the expansion of the Universe.So saysRichard Price,a physicist at the University of Texas at Brownville,who has worked out that while some objects are stretched by cosmo logical expansion,others are not .
Cosmologists,says a report on New Scientist.com have long accepted that the universe is expanding ,causing galaxies to spread apart like raisins in a rising loaf of bread,as the space between themstretches.But while Price was teaching a summer course ,a question from a high-school student floored him.
He asked me if , as space expands ,we all get bigger too, says Price.I knew the standard answer was no but I couldn’t explain why not.And when I consulted my colleagues, neither could they.
Since atoms are made up mostly of empty space,with electrons orditing the nucleus at distances typically many hundreds of times its diameter,it seemed reasonable to ask whether the electrons would be dragged away from the nucleus by the stretching of space.
Price decided to examine the simplest system, that of a hydrogen atom,with one negative electron orbiting positive proton.He found if the force involved –electromagnetic in the cases of atoms—binding the system together is stronger than a certain criticalvalue, the system will be entirely unaffected by the cosmological expansion.
This means that the solar system—which is quite tighly bound by gravity—doesn’t expand.Your desk doesn’t expandYour dog doesn’t expand, says Price.But clusters of galaxies,which are only loosely bound by gravity,will feel this effect.
Price alsofound that the atoms never experience just a little stretching –either they must ignore the expansion of the Universe or they will be completely torn apart.
This all-or-nothing effect is a startling results says Roy Maartensa cosmologists at the University of Portsmouth in the UK.
This question has been knocking around since the 1930s , but nobody has found this before.Andrew Jaffe,an astrophysicists at Imperial College London in the UK believes the effect becomes interesting in so-called big rip cosmologies in which the universe is not only expanding , but the expansion is accelerating.
Price ‘s calculation still holds in this case,but you start to see the opposite effect, says Jaffe.The expansion of the universe accelerates drastically.