Can you phone home from a black hole?

14 February 2010

Question

Is it possible to make a phone call from a black hole?

Answer

We put this question to Andrew Pontzen, research fellow at the Kavli Institute for Cosmology:

Andrew - The short answer is no, but maybe you could receive a text message. So let me take a step back and try to explain. Basically, when you make a mobile phone call the device that you're holding in your hand is using radio waves to send your voice to the person at the other end of the call. Radio waves are just a certain form of light - we can't see it directly but we receive it using antennae in our mobile phones and other devices. Because it's a form of light, just like any other light, it can't get out of a black hole. So you cannot send your voice out of the black hole, there's no way for you to have a conversation. On the other hand, light can certainly get into a black hole and in the same way radio waves can get into a black hole. So if you were to adapt your mobile phone so it could just receive text messages without having to communicate to the network, then you could actually receive a text message from your mum just before you died at the centre of the black hole.

Diana - Lovely! so no-one can hear you scream from a black hole but you could pick up a text telling you to pick some potatoes the next time you go shopping. That answer was given by Andrew Pontzen and you can hear more from him answering your science questions and keeping us up to date with space site news on our Naked Astronomy podcast available from thenakedscientists.com/astronomy.

Add a comment