Black holes are bad - but black strings could revolutionise physics....

Note: I'm getting married in under a month, so, to keep posting while full blown wedding prep goes into operation, I'm going to be focusing more on simplicity and single stories.

How we might see inside a black hole

What's worse than a black hole? Ok, yes, you could be sitting on the toilet when an angry dwarf bursts in with a crossbow an accuses you of sleeping with his girlfriend:

Oh, thank you HBO for giving me not just a picture, but a video clip to go with that line!

But, aside from that, what's worse than a black hole? Lots of them of course! A cluster of black holes may just sound like something a physicist was making to scare his kids, but there are theories of physics - theories involving space having hidden extra dimensions - that would make it possible for there to be massive strings of black holes floating through the universe.

Above: Professor Farnsworth is the man to tackle this. Better him than me.

The phenomena that could give rise to this is called 'black string': Imagine a tower, made of black holes stacked one on top of the other, stretching through the universe, slicing through whole galaxies like razor wire - that's a black string. Such a thing can exist in theory, although no-one can guess how one might form. Now, a number of questions might pop into your head if you actually encountered one of thee things, such as  'how do we escape this thing' and 'who thought it was a good idea to make a last minute bargain space tourism booking with a guy called 'The Doctor'? But the question that Roberto Emprani, of the Instituci o Catalana de Recerca i Estudis Avancats asked was: If something makes this thing vibrate, what happens to it?

Above: If you're thinking that Roberto's question is on par with asking 'what happens if I try to re-wire the big red doomsday button', you'd probably be right.

Roberto clearly has an interest in finding the answers to such terrifying scenarios of cosmic disaster, because he and his companions have developed a series of equations to find the answer: The slightest vibration causes the string to collapse into a long ribbon of black holes, joined by short necks - like a cosmic necklace of black, sucking, pearls (here's the paper). OK, that just sounds like terrifying cosmic death in a slightly different configuration, and it is, but it might - might - point the way to the of holy grail of physics: How to see inside a black hole.

Above: A quick spot by Greenwich Museums, explaining hat our theories predict could be inside a black hole.

How so and why do we care? A black string can be thought of as being a very elongated black hole, and like a black hole it has an infinitlydense singularity in the middle where all the laws of physics break down, safely cut off from the rest of our universe by an vent horizon - an impassable one-way barrier. If a string is made to vibrate, and collapses into individual black holes, the event horizon can briefly vanish along parts of its length, exposing the singularity.

If you've seen the movie 'interstellar' then you'll know that being able take data from an exposed singularity would let us unify general relativity and quantum mechanics, possibly opening the doors to faster than light travel, time travel, and a political systems that only promote honest, trustworthy politicians*.

Could this all actually happen? According to some theories our universe has more dimensions than its obvious 3 space plus 1 time. If that's true then all black holes would actually be black strings, just with their long axis oriented along the hidden, folded up, extra dimension so we only see their spherical cross section.
If that's a bit tough to visualise, imagine the good old fashioned 'rubber sheet of space' with the stereotypical gaping pit of a black hole punched through it:

Like this, the old rubber sheet with a weight visual metaphor. Although if you try to actually stretch a real rubber sheet this much you're probably going to put the weight through the ceiling in a moment.

Draw a big circle around the entrance to the hole, to represent the impassable event horizon. Now zoom in on the rubber sheet until you can see the thickness of the sheet. That thickness is the sheet's extra dimension (or extra direction) squashed down small - we exist on the surface of the space-time sheet so we can't sense it, but it's there. If the circle marking the edge of the black hole extends all the way through the sheet then it's actually a very short cylinder - or a very short string.

What if we could inflate the thickness of the sheet, expanding the extra dimensions, so we could see the black hole as a string? Well then we could watch the string collapse, and perhaps see the singularity exposed - if our card tower of theories holds together. Inflating an extra dimension like that is, in theory, possible: That's what happened to our regular 3 space dimensions just after the big bang. So, maybe, just maybe, the impassable barrier around a black hole can be beaten.

The question would then become not if we can, but if we should.....

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