Astronomy was full my freshman year, so I didn't take it. ELI5 what were looking at, why what were seeing may not be there, how we know that etc. (science is not my strong suit)
Anything we see is because light is reflected off of it or is generated by it - our eyes and brain process that reflected light into an image. Anything we see in the night sky is because of the same reason. The moon is seen because light is bounced off of it to our eyes. The stars are seen because they generate light that travels through space to get to our eyes. It takes like time to arrive at our eyes (even though it travels about 300,000 kilometers per second). On earth, it travels so fast, we can pretty much consider it instantaneous. So if we see a cup in front of us, it's because light bounced off of it and hit our eyes in negligible time. The light from the sun takes about 8.5 minutes to reach earth because of its distance from the earth, so, if we were to look at it, what we see is really how the sun looked about 8.5 minutes ago. A light-year is a measure of distance - it's the distance light travels in one year or about 9.5 trillion miles. If we see an object, like a star, that is 1 light-year away, we're actually seeing how that object looked 1 year ago since that's how long it took for the light it generated/reflected to reach our eyes. Some of the stars/galaxies we're seeing in that image are billions of light years away, so what we're seeing is how that star/galaxy looked billions of years ago. In that time, that star may have gone supernova (blown up) and been destroyed. In other words - it may no longer exist. So what we're seeing is how it technically looked in the past. To put it in perspective, some of the objects in that image are probably over 13 billion light-years away, so it's how they looked 13 billion years ago. Our solar system and the earth are just over 4.5 billion years old, so what we're looking at is how those stars/galaxies looked over 8 billion years before our solar system probably existed. If an alien race sent a communication from a planet orbiting a star out there in that pic, it would take billions of years to reach the earth just like light. When we get it, they may long be gone. Or they may still exist and have advanced so far, they're on their way here to eat us alive or enslave us. Yay!
I know this is very theoretical and that your PhD is in Dunkology and not astronomy; but is there a limit to how far in lightyears we'll be able to see? Like are these telescopes that can see farther and farther into space hitting diminishing returns? I don't often think about space beyond satellites or Star Trek movies...but this is really throwing me for a loop. It's insane to me how vast the universe is, but also how the microscopic world is almost a universe into itself... (not high, just a little sleep deprived and enjoying the sweet summer air)
Nice post! When we mention “reflected light,” should we now also say “bended light” from gravitational lensing as a 3rd category of “anything we see.” Just we don’t see that phenomenon in everyday life, but in that image …. wow!
The limit to how far back they can see is probably around the time the universe was completely opaque, which was around 380,000 to 400,000 years after the Big Bang. Once this opacity ended, it's thought 1st generation stars, also called Population III stars would have formed, which would be more massive in size than even the largest stars we've discovered so far and could in theory be detected. None have been discovered yet and although unlikely to find one, the JWST is currently our best chance at making such a discovery. The big reason it's thought discovering a 1st generation star would be difficult is because the larger the star, the faster it burns out, so chances are they've already turned into black holes or gone supernova and their gas has coalesced to join other second and third generation stars by now. Not to mention the JWST simply may not have sensitive enough instruments to find them even though it's currently our best shot.
We also happen to exist at a time that we can still see so far out and back. If the expansion of the universe continues at the rate it is the Universe will be so large and expanding so fast that we will not be able to most of it. Eventually things will get so dispersed and vast that we will not see much beyond our own local group of galaxies.
How do we know the universe is expanding though? Could it be that our galaxy is just moving? Motion/expansion is hard to tell without a reference point (again, I have no astronomy background and only took physics in high school to go to Six Flags)
Redshifting of light. Wavelengths of light are stretched further than they would be if not for the accelerated expansion of empty space between galaxies moving away from our own Milky Way. Light from some galaxies are accelerating away from us faster than in the distant past. So for instance in the early universe, dark energy wasn't as dominant as it currently is at present day, however over time, it has become the dominant energy source that is thought to be cause of the accelerated expansion of the universe. This was the big discovery found in the 90s when Hubble launched. Einstein for instance thought the universe would expand but eventually the force of gravity would cause all matter in the universe to eventually collapse into a Big Crunch. Others thought perhaps expansion would go on linearly forever. But when Hubble launched and gathered data it was revealed that the universe is not only expanding at a constant rate from the Big Bang, but is in fact accelerating it's expansion faster than anticipated. What is causing the acceleration? Scientists call it dark energy, while not fully knowing what it actually is. Some hypotheses hold the belief that empty space itself is dark energy and there's tentative experimental evidence to lay credence to it like the Casimir effect. However the measurements of the Casimir effect does not match up with the data gathered from the accelerated expansion of the universe as a result of dark energy so it's thought perhaps the accelerated expansion is from some other unknown mechanism that hasn't been explained just yet.
I am not nearly smart enough to know what I am looking at .......but DAM, its freakin awesome!!! It blows my mind that we have the technology to view this, makes you think there is someone out there besides us............we cant be the only ones in this vast universe, all this vast beauty and size for one planet??
Stuff like this gives us hope and should be prioritized in lieu of petty Earth problems. I love that Space Exploration and all is catching fire again, while my kids are still young. Going to be fun for them as they grow and see stuff like this.
