yes, we can look back in time
How do we know what happened billions of years ago in distant galaxies? Because physics only lets us see the past.
After a weekend in which a massive debate erupted in the comment section of a post discussing the merits of giving the Institute for Creation Research the ability to grant master of science degrees, one recurring theme has caught my eye. If to be scientific and objective, we need to observe and experiment, how can we possibly observe our universe and see what happened billions and billions of years ago? Hasn't time already passed so now everything that we're saying about how the universe formed and grew just guesswork?
Well, actually, on the biggest scale of them all, we can observe exactly what happened all those billions of years ago and construct a model based on direct and indirect observations. Light is a stream of photons that travel at 299,792,458 meters per second or 6 trillion miles in a given year. But wait a second here. Something doesn't add up. The nearest star, Proxima Centauri, is about 25.2 trillion miles away. A photon emitted from that star or reflected from anything that lies in its vicinity would take 4.2 years to get here. So when we look at Proxima Centauri, we see light that's been traveling over four years. And that would mean that we're seeing the star just as it was when the photons left it and are in effect, looking back at time.
The same concept will also work with the farthest objects in the observable universe, 78 billion trillion miles, or 13 billion light years away. When we look at them, we're actually looking at the dawn of the universe. Thanks to the basic laws of physics, astronomers have the ability to look into the past and even if they can't see anything visible to the human eye, they can still detect a wide variety of energies and waves that take as long as light to reach us. Our ability to see into the slow birth of our universe is only limited by our tools and as we keep going, we'll be able to see and detect more and more, giving us an ever improving idea of what was going on. Maybe, one day, with the right set of tools, we'll be able to probe down to the Big Bang itself. It's all just a question of the technology we'll need and knowing what we should be looking for when we're aiming our sensors and dial in on the right part of the sky.
