Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 02/05/2012 14:13:16

Title: When looking at distant objects, are we looking at the past?
Post by: thedoc on 02/05/2012 14:13:16

I’d like to know about seeing things light years away.  I understand that we see things when the light arrives to our vision on Earth, but I wanted to ask when we see objects light years away, are we looking into the past?  
Asked by Katherine, Hemel Hempstead


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[chapter podcast=3948 track=12.04.29/Naked_Scientists_Show_12.04.29_10069.mp3](https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.thenakedscientists.com%2FHTML%2Ftypo3conf%2Fext%2Fnaksci_podcast%2Fgnome-settings-sound.gif&hash=f2b0d108dc173aeaa367f8db2e2171bd)  ...or Listen to the Answer[/chapter] or [download as MP3] (http://nakeddiscovery.com/downloads/split_individual/12.04.29/Naked_Scientists_Show_12.04.29_10069.mp3)

Title: When looking at distant objects, are we looking at the past?
Post by: thedoc on 02/05/2012 14:13:16

We answered this question on the show...



Chris - Effectively, yes you are.  Light travels at 300,000 kilometres a second – very, very fast.  Rather than report distances in terms of miles, kilometres, or metres in space, it’s more convenient to say, “how long would light, travelling at the speed of light, take to go from where it started to us here on Earth?”  And actually, it conveniently works out as about a billion miles an hour.
So if you sent a radio message, which is a form of light, between the Earth and Pluto, Pluto is about 6 billion kilometres away, so it would take about 6 hours for your message on your mobile phone or your signal to go from here to Pluto.  If someone then sent a message back from Pluto, it would again take about 6 hours for that message to come back.  So it’d be a pretty slow conversation.  
So in other words, yes, there's been a very big delay in time between the time that your message was sent from one place to the other place and that means a time lapse must have happened because light has a finite speed at which it can travel.

Title: Re: When looking at distant objects, are we looking at the past?
Post by: myself on 04/06/2012 02:33:08

Not really.  Photons don't do time, so they have no past or future.  And you can't actually be certain it started where you think it did.  It might have been distorted on the way.  The more photons you collect, though, the more confident you can be that they mostly represent an actual past.