# Seeing Back in Time? **URL:** \ **Category:** Factual Questions\ **Created:** [January 18, 2010, 2:29pm UTC](https://boards.straightdope.com/t/seeing-back-in-time/525421 "2010-01-18T14:29:19Z")\ **Posts on this page:** 4\ **Page:** 2
**Author:** ![RedSwinglineOne](https://avatars.discourse-cdn.com/v4/letter/r/a9adbd/32.png) [@RedSwinglineOne](https://boards.straightdope.com/u/RedSwinglineOne)\ **Post date:** [January 19, 2010, 5:29pm UTC](https://boards.straightdope.com/t/seeing-back-in-time/525421/21 "2010-01-19T17:29:04Z")
> [@Exapno\_Mapcase](#): > > Moving a camera in our time closer to a supernova that took place 1000 years ago wouldn’t capture any images from before the supernova, no matter how fast you got the camera closer. I believe the point was to move the camera further away. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [January 19, 2010, 5:59pm UTC](https://boards.straightdope.com/t/seeing-back-in-time/525421/22 "2010-01-19T17:59:21Z")
Ah, I get it. Though that makes the ability to see the planet, and especially the people on the planet, even less plausible. ---
**Author:** ![Anne\_Neville](https://avatars.discourse-cdn.com/v4/letter/a/b9e5f3/32.png) [@Anne\_Neville](https://boards.straightdope.com/u/Anne_Neville)\ **Post date:** [January 19, 2010, 6:29pm UTC](https://boards.straightdope.com/t/seeing-back-in-time/525421/23 "2010-01-19T18:29:32Z")
> [@The\_Hamster\_King](#): > > The earliest we can see is the [cosmic microwave background radiation](http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation). When we look at it we’re actually looking at the “hot fog” that filled the universe for the first several hundred thousand years of its existence. During that era the universe was opaque, so we can’t see any further back. They are, however, very interested in finding things other than the microwave background as far back in time as they can (called high-redshift or high-Z galaxies). These can tell us about how galaxies formed and how they evolve over time. > [@LiveOnAPlane](#): > > Additionally, we need to keep in mind the possible resolution from far distant objects even when they can be seen. We might be able to see a star, but even with infinite resolution, we could never see people on a planet circling htat star; there just aren’t enough photons coming to us to build a picture at that level of detail. > > …unless, of course, you have CSI: Miami enhancement software available to you. Even if you did get enough photons, you’d need a ridiculously huge telescope to do it. If you wanted to do something far more modest- say, see the flag that the astronauts planted on the Moon- you’d need a telescope [805 feet in diameter](http://www.rocketroberts.com/astro/flag_on_moon.htm). And that’s just to see a blob- to see it actually look like a flag, you need something more like three and a half **miles** in diameter (all this is ignoring atmospheric effects). If we want about 10 cm resolution (that’s what spy satellites supposedly have) to see something on a planet of Alpha Centauri, you’d need a telescope a billion miles in diameter. That’s a little bigger than Saturn’s orbit around the Sun. The Crab Nebula is 6500 light-years away, so that’s even worse. The telescope would have to be something like half a light-year in diameter. ETA: The largest optical telescope in the world is 10.4 meters in diameter. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 19, 2010, 6:48pm UTC](https://boards.straightdope.com/t/seeing-back-in-time/525421/24 "2010-01-19T18:48:02Z")
> [@](#): > > The earliest we can see is the cosmic microwave background radiation. When we look at it we’re actually looking at the “hot fog” that filled the universe for the first several hundred thousand years of its existence. During that era the universe was opaque, so we can’t see any further back. That’s the limit for light (any kind of light, including radio, x-rays, etc.), but you can in principle see back further with other forms of radiation. For the CMB, we’re seeing the Universe as it was approximately 300,000 years after the Big Bang. With the equivalent in neutrinos, we should be able to see back to about 200,000 years after the Bang, though detecting neutrinos at that low an energy is tricky. And in principle, using gravitational waves, we think we ought to be able to see back to about 10[sup]-26[/sup] seconds after the Bang, but that’s well beyond our current technology: We’re still a few years away from detecting any gravitational waves at all, and it would probably take a device about three generations more advanced than that to detect the cosmological background. [Previous page](https://boards.straightdope.com/t/seeing-back-in-time/525421.md?page=1)