Light years?

[Dicart]

Or slows down. Or moves (somehow) further away. But suppose the observer changes position?

Dave answered my question in part - that it wouldn’t slow down in a vacuum, that it remains constant but this assumes it would change if the way it was traveling (no longer in a vacuum) changed, yes?

No, the light do not slow down (his speed) because of the movement of the object who is emmiting it.
It can only (not only but let do it simple) slow down because of the density of the matter it is traveling through, and this latter point has nothing to do with the movement.

 

[DaveC426913]

Sorry wegs, blame me. Dicart has become more interested in denigrating me then actually addressing the questions you asked.
Nevertheless, his digression may serve to inspire more questions from you.

But I think we should let you drive the questions rather than mansplaining to you in some sort ego contest.

 

[Beer w/Straw]

Does light move slower due to gravity?

 

[DaveC426913]

Does light move slower due to gravity?

Yes and no. It's nuanced.

The short answer is:
Light rising out of a gravitational field does not slow down; instead its gets red-shifted.
The longer answer gets into some edge cases that are harder to grasp easily.

 

[wegs]

Sorry wegs, blame me. Dicart has become more interested in denigrating me then actually addressing the questions you asked.

lol There must be a backstory there that I’ve missed.

But I think we should let you drive the questions rather than mansplaining to you in some sort ego contest.

No worries. Hopefully, that adage “no question is stupid, only the one you didn’t ask” applies here.

Okay, so how can we ever know what distant galaxies look like in the present? Are we only looking at things now, that were from the past? (from a light year perspective)

Is there no such thing as “right now” when we’re talking about other galaxies, and outer space in general?

 

[Dicart]

Sorry wegs, blame me. Dicart has become more interested in denigrating me then actually addressing the questions you asked.
Nevertheless, his digression may serve to inspire more questions from you.

You think i am denigrating you because probably of your own ego (you resist the fact you could have been wrong, one time in your life).
I only pointed obvious errors (this is at least what think it is) and instead of discussing and debate about what i said (and if you are right you should be able to defend your own position) you are talking about ... me (i am a troll etc).
This is not how science work.

 

[DaveC426913]

Okay, so how can we ever know what distant galaxies look like in the present?

We've assembled enough observations that we have a pretty good idea of what billion year old galaxies are that are more than a billion years old.
We may not know what a specific galaxy looks like "now", but we see other galaxies that are older than the one we're currently looking at, and we can project what it ought to look like.

But frankly, it's kind of meaningless to wonder what a galaxy a billion light years away looks like "now". It is forever separated from us by that billion light years.

Are we only looking at things now, that were from the past? (from a light year perspective)

Essentially, yes.

Dicart is correct in one respect: there are basic answers and there are more advanced answers - for those with some knowledge under their belt. When Dicart says "That is wrong." what he really means is "that is simplistic; there's more to it than that." I'm sparing you the details until and unless you express an interest in a deeper dive.

Is there no such thing as “right now” when we’re talking about other galaxies, and outer space in general?

Essentially, true. Unlike Newton's view of the universe, Einstein's universe is based on the postulate that there is no such thing as a universal time.

 

[Seattle]

lol There must be a backstory there that I’ve missed.

No worries. Hopefully, that adage “no question is stupid, only the one you didn’t ask” applies here.

Okay, so how can we ever know what distant galaxies look like in the present? Are we only looking at things now, that were from the past? (from a light year perspective)

Is there no such thing as “right now” when we’re talking about other galaxies, and outer space in general?

You can't see a distant galaxy in the present. You don't see the Moon in the present but the delay is minimal. You don't see the Sun in the present, the delay is about 8 minutes.

I was going to address relativity and the constant speed of light but Dave just did that.

 

[DaveC426913]

You think i am denigrating you because probably ...

Show some respect for the OP and stay on-topic. Troll elsewhere.
Reported for off-topic trolling.

 

[wegs]

You can't see a distant galaxy in the present. You don't see the Moon in the present but the delay is minimal. You don't see the Sun in the present, the delay is about 8 minutes.

So we (humans) are only ever seeing the sun, stars, moon…in their past?

 

[Seattle]

So we (humans) are only ever seeing the sun, stars, moon…in their past?

Yes, that's the nature of light having a speed and not being instantaneous. It's possible that the large star Betelgeuse (brightest star in Orion) isn't even currently in existence. It's due to become a Super Nova anytime within the next few thousand years or it could have already happened. We wouldn't know yet because of its distance from Earth.

 

[Dicart]

Show some respect for the OP and stay on-topic. Troll elsewhere.
Reported for off-topic trolling.

Me too.
Dont try to scare me.

 

[DaveC426913]

So we (humans) are only ever seeing the sun, stars, moon…in their past?

Everything beyond the tip of your nose is seen as it was in the past.

Your perception can't really tell the delay for distances closer than anything on Earth.
Even our highest satellites, 36,000km up, have only a tenth of a second delay.

Remeber though: it's pretty meaningless to talk about what distant object might like "in the present". The speed of light is the speed limit for all of nature, so there's no universal "now".

 

[Michael 345]

#1 - Deep Field: SMACS 0723
NASA’s Webb Delivers Deepest Infrared Image of Universe Yet

Status: 1st Image Released 12/July/22 ~10:39am EDT



NASA's James Webb Space Telescope has produced the deepest and sharpest infrared image of the distant universe to date. Known as Webb’s First Deep Field, this image of galaxy cluster SMACS 0723 is overflowing with detail.

Thousands of galaxies – including the faintest objects ever observed in the infrared – have appeared in Webb’s view for the first time. This slice of the vast universe is approximately the size of a grain of sand held at arm’s length by someone on the ground.

Thought this would be of interest

If you have the app lots of pictures will be coming

 

[parmalee]

To be much clearer let say the same thing with the same units :
"So A galaxy one billion light years from us has light reaching us having travelled one billion light years."

1. There is no galaxy at one billion light year.
2. If you consider that it was some galaxy (at least) one billion light years away from us when it emmited the light, the light could not have traveled one billion light years, because of the expansion : It has traveled more.

I'm not entirely clear as to how you think saying this differs, say, from saying something like this:

"It would be inaccurate for me to state that my dog is 15 years old, because, in the time that I have said such, she has already aged that much more."

In other words: sure, but what exactly would be the point of expressing what Dave has already expressed succinctly in the rather more convoluted--and, by no means, any more accurate--manner that you have expressed above?

 

[Dicart]

I'm not entirely clear as to how you think saying this differs, say, from saying something like this:

"It would be inaccurate for me to state that my dog is 15 years old, because, in the time that I have said such, she has already aged that much more."

In other words: sure, but what exactly would be the point of expressing what Dave has already expressed succinctly in the rather more convoluted--and, by no means, any more accurate--manner that you have expressed above?

The point is you can speak of your dog like this because you are wrong, he has not aged much more but only a bit more and this is neglectable.
You can not speak of a galaxy like you are speaking of your dog barking around you.
Here we are speaking of billions of years, not of nanoseconds (thats propably the point you dident see).

You do the same considerations when you consider that SR apply or not, it depends if there is something significant or not.

When you do cosmology you need to take this in account, not if you speak of everydays things.

 

[Sarkus]

I think the point is that, for the level that the OP is at in their understanding of the topic, trying to be precise, rather than just conveying the basics, will be more likely to confuse rather than help. Introducing concepts such as expansion is thus likely a step too far at this stage.

 

[Dicart]

I think the point is that, for the level that the OP is at in their understanding of the topic, trying to be precise, rather than just conveying the basics, will be more likely to confuse rather than help. Introducing concepts such as expansion is thus likely a step too far at this stage.

I think that when we are talking about cosmology, conveying wrong basics will confuse the OP soon or later.

 

[wegs]

Everything beyond the tip of your nose is seen as it was in the past.

Your perception can't really tell the delay for distances closer than anything on Earth.
Even our highest satellites, 36,000km up, have only a tenth of a second delay.

Remeber though: it's pretty meaningless to talk about what distant object might like "in the present". The speed of light is the speed limit for all of nature, so there's no universal "now".

Thanks for your explanation and it’s been very helpful. Also thanks for not making me feel stupid like a few others in this thread.

A light year measures distance not time so perhaps it seemed like someone asking how many minutes are in a mile? lol It’s much clearer now to me, but I have other questions now that this is out of the way.

 

[parmalee]

The point is you can speak of your dog like this because you are wrong, he has not aged much more but only a bit more and this is neglectable.
You can not speak of a galaxy like you are speaking of your dog barking around you.
Here we are speaking of billions of years, not of nanoseconds (thats propably the point you dident see).

Thanks for telling me what I "dident see." Not sure how you came to that conclusion, but I'd posit that you don't seem to "see" perspective. Neither do you seem to grasp scale, for that matter.

You do the same considerations when you consider that SR apply or not, it depends if there is something significant or not.

When you do cosmology you need to take this in account, not if you speak of everydays things.

Again: sure. Bu,t also, again: the post of Dave's is not "wrong" in that regard. It is not exhaustive, i.e., does not address expansion, etc., but neither does it profess to be. There's a difference between incomplete and incorrect, yes?

Edit: Also, if we're going to be persnickety... nanoseconds? Seriously? The units of time by which we measure the time it would take to convey a sentiment somewhat more complex than a simple yay or nay would likely be seconds--not thousands of milliseconds or millions of nanoseconds. Again: scale.