Why limited discussion of only looking at history

[CONANGIB]

When you look at a bird in a tree with binoculars, that is not the bird as it exists at the moment but the bird that was there before the light traveled to the scope, which for practical purposes is the bird. You can shoot the bird of before, and it will fall to the ground.

However, when you look at a distant object in a larger telescope, you are looking only further into the past. And we describe our existence and our history from that observation. Yet looking at the most massive galaxy in the known universe, it could in all probability not be there at the moment you look at it. You are looking only at where it was at the time when the light started moving toward the observer. So we are not describing the universe but what use to be in a particular area. How can we say this is this, and make these calculations and theories when we should understand we are looking only at something in the past. And the larger question, why don’t physicist talk more about this?

 

[russ_watters]

So we are not describing the universe but what use to be in a particular area. How can we say this is this, and make these calculations and theories when we should understand we are looking only at something in the past.

This is actually a benefit, not a hindrance. Since the universe is fairly homogeneous, we have its complete history laid out in front of us to look at. Biologists wish they could be so lucky to have a complete fossil record laid out for them with no need to dig!

And the larger question, why don’t physicist talk more about this?

It is certainly a well known, discussed and understood feature.
https://www.google.com/search?q=hub...droid-verizon&sourceid=chrome-mobile&ie=UTF-8

 

[DaveC426913]

How can we say this is this, and make these calculations and theories when we should understand we are looking only at something in the past.

Why is that a problem?
What difference can it make what it is doing right now, if we only have access to it when its light reaches us.

In your bird example, you are shooting at the bird of the past. Your bullet only travels at a few Machs. The bird may leave the perch by the time your bullet reaches it. But what can you do about it?

 

[ZapperZ]

When you look at a bird in a tree with binoculars, that is not the bird as it exists at the moment but the bird that was there before the light traveled to the scope, which for practical purposes is the bird. You can shoot the bird of before, and it will fall to the ground.

However, when you look at a distant object in a larger telescope, you are looking only further into the past. And we describe our existence and our history from that observation. Yet looking at the most massive galaxy in the known universe, it could in all probability not be there at the moment you look at it. You are looking only at where it was at the time when the light started moving toward the observer. So we are not describing the universe but what use to be in a particular area. How can we say this is this, and make these calculations and theories when we should understand we are looking only at something in the past. And the larger question, why don’t physicist talk more about this?

I don't understand this last part. Physicists (and astronomers and astrophysicists) DO talk about this, and talk about it a lot! It is why the CMB is always touted as the light during the INFANT universe, etc...etc. and why studying it is so important on understanding the early universe! Did you sleep through that?

I seldom fail to hear the claim that when we look at our most distant stars or galaxy, we are peering back into time. I have heard this many times, both in TV documentaries (please watch both versions of "Cosmos") and in print. So your assertion here that these were seldom mention is very puzzling. Maybe you don't remember them, or missed them. But do not confuse that with us neglecting such things.

Zz.

 

[gmax137]

Also keep in mind that there is nothing happening on that far distant star "now" that can affect us here any sooner than the light leaving the star "now" arrives "here."