Saturday, April 04, 2009

What would it look like to fall into a black hole?


21:46 01 April 2009 by
Stephen Battersby
Video:
Falling into a black hole would be a one-off sightseeing trip, so this simulation,
calculated by Andrew Hamilton and his team at the
University of Colorado,Boulder, is a safer option

Falling into a black hole might not be good for your health,
but at least the view would be fine. A new simulation shows what you might see
on your way towards the black hole's crushing central singularity. The research
could help physicists understand the apparently paradoxical fate of matter and
energy in a black hole.
Andrew Hamilton and Gavin Polhemus of the University of Colorado, Boulder,
built a computer code based on the equations of Einstein's general theory of relativity,
which describes gravity as a distortion of space and time.
They follow the fate of an imaginary observer on an orbit that swoops down
into a giant black hole weighing 5 million times the mass of the sun, about
the same size as the hole in the centre of our galaxy.
As you approach, a dark circle is bitten out of the galaxy containing the
black hole, marking the event horizon – the point beyond which nothing can
escape the black hole's grip. Light from stars directly behind the hole is
swallowed by the horizon, while light from other stars is merely bent by the
black hole's gravity, forming a warped image around the hole.

Horizontal ring
To distant observers, the horizon has a size of one Schwartzschild radius
– about 15 million kilometres for this hole – but as you approach, it recedes
from you. Even after you cross this radius, there is still a point in front
of you where all light is swallowed, so from your point of view, you never
reach the horizon.
Hamilton and Polhemus have painted a red grid on the horizon to help visualise
it (as the horizon is spherical, the two circles on the grid represent the
north and south "poles" of its central black hole). And as you pass one Schwartzschild
radius, another artificial visual aid pops up. The white grid that loops around
you marks where distant observers would place the horizon – this is where
you'd see other people falling in if they followed you through the horizon.
The strangest sight is reserved for your last moments. So close to the
centre of the black hole, you feel powerful tidal forces. If you're falling
in feet first, gravity at your head is much weaker than at your feet. That
would pull a real observer apart, and it also affects the light falling in
around you - light from above your head is stretched out and shifted to the
red end of the spectrum. Eventually it gets red-shifted into nothingness,
so your whole view will be squeezed into a horizontal ring.

Information paradox
This process might shed some light on a black hole puzzle. Quantum calculations
seem to show that there is too much complexity within a black hole - in earlier
work, the researchers calculated that it should be possible to create much
more entropy (a measure of disorder) inside the black hole than is measured
by outside observers.This is like a supercharged version of the
old black hole information paradox, which pits the apparent destruction of
objects - and information - that falls into a black hole against quantum mechanics,
which states that quantum information can never be lost.The problem may
be that we have a naive view of space, which breaks down
inside the black hole. To calculate total entropy, Hamilton and Polhemus assumed
that you add up all the possible states that matter and energy could take
at different points in space. But along with other theorists, they suspect
that this usual assumption, called locality, doesn't work inside a black hole.
Somehow, different points in space seem to share the same states - but it's
not clear how.
That's where visualisations like this might just help. "Close
to the singularity, it appears that the entire three-dimensional universe is
being crushed into a two-dimensional surface," says Hamilton
(see
Our world may be a giant hologram). But whether it hints that a
2D view is more fundamental is not yet clear. "Does it have any profound significance?
I don't know," says Hamilton.

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