# Time-travel Viewer

by jackchen
Tags: timetravel, viewer
 P: 14 Now, we all know from our own telescopes and stuff, we manage to capture images (light) from stars 1000 light years away from us. Thus what we capture is what the stars look like 1000 years ago. They could look different now. So, assuming at this instance, I have a telescope-camera placed 65million light years away from Earth, I'll be able to see dinosaurs?
 Sci Advisor P: 2,194 Simply on the basis of the fact that light takes time to reach the destination, yes you would be able to "see" the dinosaurs. Note, however, the size of the telescope you would need. Assume that if you want to "see" the dinosaur, you want to resolve features a tenth of a meter across. A pixely dino, but it will have to do. Unfortunately for you, at a distance of 65 million light years, a .1m feature subtends an angle of about 3*10^-20 arcseconds. Assuming perfect resolution in your telescope, you'd need a mirror with a diameter of about 440 light years to even resolve the beasts. There is also the little problem of the fact that the dinosaurs are giving off almost no light, at least compared to sources normally viewed from 65 million ly distant. In fact, for every squared meter of detector you can expect one photon to arrive from your cute cuddly buddy about once every 10^20 years. Fortunately for us, our 440 ly diameter mirror has an area of about 10^37 m^2! So we can expect a nice flux of about a couple hundred million photons a second. Still, not exactly like watching cable.

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