OK, I'm looking into the night sky through a telescope and I observe a different galaxy. It is this specific amount of light years away. Here is what confuses me:
If it takes this specific amount of years for the light to reach out Earth,then how do we know how it looks today?
expand that to the background radiation of the entire universe. YES we know how the universe looks billions and billions of years ago, but as time goes by, how do we know how the Universe looks at this specific moment in time?
If it takes this specific amount of years for the light to reach out Earth,then how do we know how it looks today?
expand that to the background radiation of the entire universe. YES we know how the universe looks billions and billions of years ago, but as time goes by, how do we know how the Universe looks at this specific moment in time?
-
There's no way to know any drastic changes. If a sun that was 20 light years away blew up, we would take 20 years to see that explosion. There is no quicker mode of transfer than light.
Similarly, we can't use telescopes to formulate an understanding of where everything is. That's where red shift comes in. Using that, we can tell how far away something is A CERTAIN TIME AGO, and how fast it's moving. Using complicated physics, we can estimate where it is NOW, and we can continue to tell, because it will keep moving the same way.
Similarly, we can't use telescopes to formulate an understanding of where everything is. That's where red shift comes in. Using that, we can tell how far away something is A CERTAIN TIME AGO, and how fast it's moving. Using complicated physics, we can estimate where it is NOW, and we can continue to tell, because it will keep moving the same way.
-
You don't know how it looks today. In fact, it might not even be there today. Works for our Sun, too. Only what you see of it is only 8 minutes old because it's way closer than that galaxy. That is, the Sun could snuff out right now but we would not lose its gravity pull and its light until 8 minutes later, the time it takes things at the speed of light to travel 93 million miles from the Sun to Earth. And, yes, gravity also travels at light speed.
And yep, the speed of light limit applies to all things in our universe. So nothing we see out there is as it is now; they are all old news.
BTW there is really nothing relativistic here...unless you want to say the speed of light limit is relativistic. It isn't you know. The speed of light was confirmed years before the theories of relativity came into being. In fact, that the speed of light is the same no matter what was the major drive for forming the special theory of relativity. In other words C begat the theory, the theory did not begat C.
And yep, the speed of light limit applies to all things in our universe. So nothing we see out there is as it is now; they are all old news.
BTW there is really nothing relativistic here...unless you want to say the speed of light limit is relativistic. It isn't you know. The speed of light was confirmed years before the theories of relativity came into being. In fact, that the speed of light is the same no matter what was the major drive for forming the special theory of relativity. In other words C begat the theory, the theory did not begat C.