• Question: How do we know that a black hole is a geometrically defined region of spacetime that has such a strong gravitational pull that nothing can pass through it , when we can't get anywhere near it?

    Asked by 758rhed26 to David, Eva, Nicholas, Rachel on 18 Nov 2015.
    • Photo: Nicholas Pearce

      Nicholas Pearce answered on 18 Nov 2015:


      Hello,

      Black holes were thought about long before we knew if they actually existed! If Einstein’s famous theory of general relativity was looked at, it predicted that tiny regions of spacetime with lots of mass (and therefore gravity) formed that they could have so much gravity not even light could travel fast enough to escape from them.
      Scientists worked more on this prediction and lots of what we know about black holes are just ideas about them. As these ideas developed more, we started looking for black holes and knew what to try and look for.
      Eventually we were able to find black holes based on the properties predicted by these theoretical scientists. That’s how we know lots about them – we know what they *should* be like and then found things that matched the predictions!
      Here is a great video about what it would be like to travel inside a black hole: https://www.youtube.com/watch?v=3pAnRKD4raY
      It’s all based on predictions based on what we currently know about black holes.

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