Question About the Universe

Hey Stile, cheers.I suppose that there is some basic aspect of optics that I am not remembering but I was wondering why distant objects do not appear much larger than they are if the light from them is spreading out in all directions. Larger and all fuzzy.Either that or why we don't see distant stars getting farther apart from each other in directions other than directly down the line of sight. Or do we see that?Edit; If there are 2 stars that are 100Mpc apart from each other today. Tomorrow they will be 10.6 million km farther apart. 100 million km in 10 days. If our line of sight is perpendicular to their separation, why do we not see that distance increasing? Or do we?Edited by Prototypical, : No reason given.

Ahhh... but they do.
They don't seem so much "larger and fuzzier" though... 'cause that's not how light works. They do, however, seem fainter.Here's an example:Let's say I'm on a mountain top with a flashlight.
You are on another mountain top a mile or so away from me.
I shine the flashlight directly at you.We know that the light coming from a flashlight expands out. By the time it gets to you, a mile away... the light from the flashlight would cover a surface area of possibly a few square miles!
But... I'm sure you can tell from your past experiences... you do not see me with a light that is a few square miles large. You see a tiny little speck of a flashlight off in the distance.Why?Because we only see what our eyes detect.Yes, the light from the flashlight is expanding all over the place.
But, as far as you're concerned, you still only see the light photons that hit your eyes.
Also... your brain processes this information (as well as all the other photons that are hitting your eyes from other sources...) into the image that you "think you see" when your eyes are open.
(^^... this is awesome...)-------------
Total awesome aside thing:
-the image you see isn't really "physical stuff in front of you that you see."
-the image you see is more "a picture created by your brain that is developed from the input information from your eyes."
That is, you may feel like you are "seeing out your eyes"... but you're not. You're just "seeing" an image that is created from within your brain... inside your head Kind of like you may feel that "your thoughts" are above your head, or maybe up and in front of your head a bit... but they all reside in your head, between your ears. Ancient greeks/romans (before modern medicine) used to think "their thoughts" were located in their chest, where their heart was, even.Example: Think of a barcode scanner hooked up to a computer and a monitor. The scanner (your eyes) scans the barcode (real world) and the computer (your brain) processes the information and spits out the numbers that the barcode stands for to the monitor (the image "you see"). From this, you "see" the numbers from the barcode... but you don't actually see the barcode itself... reality could be filled with "barcodes" even though the image our brain processes decodes these into "useful numbers."
Heh... I think that's awesome
Ceci n'est pas une pipe
-------------Now, to explain the "faintness" of the flashlight.Let me just pick some numbers here for illustration.
Let's say the flashlight sends out 1 billion (1 000 000 000) photons.
If you're up close to the flashlight, maybe 80% will hit your eyes... 800 000 000 photons. This will be bright.
Now, let say you back up some distance, and maybe only 10% of the photons hit your eyes... this will be a lot fainter.
Now, on your mountain top, about a mile away... maybe only 0.00145% of the photons hit your eyes... obviously, the "light you see" will be very faint (down to 14 500 photons).At some distant point, the photons from the flashlight will diffuse so much and get so far apart from each other... that your eyes will be able to fit in "the gaps" and you won't see any light at all, even if there is nothing between you and the flashlight except for space. You will simply be "too far away to see it." Or, as we generally say, the light will be "too faint to see."
The more powerful the light, the more photons are sent out, and the farther away you can be until you get into "the gaps" and cannot see the source.Now, it is interesting to note that the individual photons don't actually stop. They're still going... on and on through space. Past you and beyond you. If you had massive, huge eyeballs that picked up more photons... you would be able to see the flashlight again. It's just that your eyes are small enough to fit into the gaps at this distance. And, therefore, you can no longer detect the light."The gaps" don't even have to be complete, 100% gaps. It's also more like... not enough photons from the source in a certain amount of time are hitting your eyes in order for your brain to process an image out of them. At some point, a few photons from the light source will hit your eyes... but your brain just won't acknowledge them (will consider them "noise").Light sources send out photons in all directions, all the time. But it's not like strict directions. That is, it's not like you could be at some far distance and shift your head 2 inches to "see the photon stream" and then shift your head back 2 inches into "the gap" and the light disappears. That's not how it works. It's more like... random wave-streams of photons constantly expanding away from the light source. When you can no longer see the source... it just means that the photons have diffused out so much that the random gaps are large enough to render your means of detection (your eyes and brain) useless.Does that help? Starting to get past my level of physics.
But, I'm pretty sure we do see this.
I'm pretty sure we see everything getting farther apart from everything else, everywhere. No exceptions.
(Edit: ^^^This above line is not entirely true. Or, at least, it's misleading. Please see Message 53 for some details, if interested).Which is exactly why we know that space is expanding. Again, these specifics are beyond me for what we have and have not observed.
But I would guess that we have seen this, and we do see this.
Just out of curiosity... I know that a Mega parsec (Mpc) is very, very large... maybe 10.6 million km and 100 million km aren't all "that large" in comparison to 100Mpc.
I would do that comparison first, if I were you. Then see what sort of percentage increase this is and see if it would be something that would actually be easy to detect or not.Hopefully, if I'm getting totally off base, someone with more experience in these matters can pop in with an answer.Edited by Stile, : It's just a picture of a pipe, sillyEdited by Stile, : Correcting mah ignorance

The light that spreads out in directions that are not towards you never reaches your eye. So it cannot contribute to how large the object appears or how bright the object appears. What you see is only the light that travels in the direction along the line of sight between you and a star.Now if the object were surrounded by a cloud of dust so that the light that as it spreads out can be reflected or re-radiated in your direction, then you can see a larger bright image resulting from the star.

Exactly. 100 Million parsecs is about 326 million light years, while 100 million km, is about 6 light minutes. (The earth/sun distance is about 150 million km).In fact even without considering the expansion of space, stars do move relative to each other (proper motion). Over long periods of time, we do see the shapes of constellations change due to relative motion of the stars. The link below shows how the Big Dipper is expected to change over long periods of time. Page not found | Department of Astronomy

Because that means that the increased angle of separation between them, from where we're sitting, is 0.00000000000117 degrees, or to put it another way, the angle subtended by a typical bacterium if it was on the Moon. You couldn't see that, could you?

Cheers again for all that typing you did there. That's like the mother of all answers! I think that I have a grasp on diffusion and dimness. I guess what I am trying to understand is if my intuitive concept of expansion is the same as the way the universe is expanding.I was trying to eliminate the 'normal' diffusion of light out of the question by considering streams of single photons on parallel vectors. Would those 2 streams experience diffusion caused by the expansion of space?Or if you projected a stream of single photons at a receiver would the expansion of space require that you adjust the beam in order to maintain the line of sight?

No I suppose not.If I imagine an equilateral triangle consisting of my eye and any two stars. As the universe expands will that triangle remain equilateral?

Well. Fuck me sideways.
Thanks for the questions, I just learned some important shit over here.I had written a response of rambling junk. Then I decided to look up a quick google and did me some learnin'!In my last post, I said something like "everything, everywhere is expanding" due to the expansion of space.
This is not actually true.Only space is expanding, everywhere and in every direction.
Think of it like a force.A desk is made of atoms but mostly empty space, right?
Well, all the "empty space" inside the desk is expanding.
However... the desk itself as an object is not expanding.The forces holding the atoms of the desk together (electromagnetic? strong? weak? whatever, I don't know....) are strong enough to overcome the expansion of the space within the desk.Therefore, an 80 cm wide desk will never expand. It will always remain 80 cm wide.
But... if we have two 80 cm wide desks floating in space... 100 Mps apart... then they will get farther and farther apart by about 100 million kms every 10 days... as you mentioned in your previous message. (Assuming your math is right, I didn't check it or anything).Hopefully that makes sense. Mystery of the Expanding UniverseSo, armed with this knowledge, I will attempt some guesses at your questions: No. ...kinda.
I don't like the term "diffusion" as it seems to suggest that the streams would spread out in a non-parallel-like fashion.
The direction of travel of the two streams would always be parallel at any specific point in time you cared to look at them.
However, the distance between the two streams would, in fact, increase due to the expansion of space.Maybe at the source, the two streams were 1 million kms apart.
After travelling through 100 Mps of space... the streams would be 101 million kms apart (or something like that... again, I'm not doing any math, just trying to use some numbers as an example).Please note, though... that at all specific points in time, the direction of travel of the two streams are always parallel.So I would say... no, they do not experience "diffusion."
They do, however, experience "expansion." Never.
The receiver would always be there.
The stream of single photons would always be directed at the receiver.
Expansion of space would not alter either of these two facts.Expansion of space would, however, alter the frequency at which individual photons were detected by the receiver. The amount of space between the emitter and receiver would expand and therefore increase. Unless they were fixed to each other... like being in the same room or something. But if they were in space... then they would expand away from each other.As they expand away from each other... the photons take longer and longer to get from emitter to receiver.As the photons have more time to travel from emitter to receiver... the space between each photon in the stream will also expand more and more as the photons travel.Therefore, the time difference between photons hitting the receiver would increase....I think, anyway. Sounds legit to me *******
(Old, silly post is hidden after this point, if anyone wants to see how stupid I used to be. I refuse to delete it 'cause I spent time on it. So there )
*******
(Use the "Peek" button in the bottom right of this post to view my hidden shame) Edited by Stile, : Just learning. Always learning. Stupid learning... what did I ever do to you!

Probably not. Stars are not stationary relative to each other even once expansion of space is subtracted out. For example, the stars in the Andromeda galaxy are moving towards the Milky Way and earth, and we expect that the two galaxies will collide at some point.I understand that what you are really mean to is whether the expansion of space is isotropic (uniform at all points and in all directions). I think there is some evidence that the acceleration of the expansion is at least slightly non-uniform.Page not foundEdited by NoNukes, : No reason given.

Electromagnetic.

I was under the impression that the increasing distance between galaxies is not the same as the increasing distance between me and a ball that I have thrown. Galaxies are not moving through space but rather new space is being created(?) or introduced between them.Experience tells me that you need some kind of pressure to squeeze that new space in between those galaxies given that space is actually a thing. So if dark energy is responsible for the expansion of space and the increasing distance between galaxies, am I right to think of it behaving in the same way that forces work locally? Dark energy has to overcome the mass of all the galaxies in order to move them? In order to do that it must be pushing 'off of' something else.edit; And it would increase equally down the entire length of the streams?Edited by Prototypical, : No reason given.

Sort of I guess but I was wondering if the expansion has any effect on light in directions other than down it's direction of travel. It stretches the light but does it bend it in any way?

This is true. Those two things are certainly not the same.What I meant by "this of it like a force" was that the new space that is being created doesn't necessarily push everything out of the way. That is, if two things are linked with other forces (gravity, electromagnetic, or any of the others...) it is possible that the forces that link them together will be greater than the "force" from the expansion of space. If so, then the objects will not move apart. I don't know. Sorry... I'm not entirely sure what you mean.
"The stream" of photons isn't a single thing. It's a bunch of individual photons.
The rate at which they distance themselves from each other is the same down the entire length of the streams.However, when the photons are closer to the emitter, this rate will not have much time to act on them. Therefore the parallel streams would be closer.
Then, as the photons are farther and farther away from the emitter... the rate of expansion has more time to act on them and therefore the parallel streams will be farther and farther apart from each other. I don't know for sure.
But I would guess "no."
Light does get bent, but due to the effects of gravity. I think.

Doggonit. Why do you guys repeat this stuff? For at least the third time... with respect to galaxies, the answer is that both types of changes in separation are happening. Galaxies do move relative to each other in exactly the same sense that a ball moves relative to you. For example, the Andromeda galaxy is actually moving towards the Milky Way and the two galaxies will collide at some point.There is also the effect of increasing separation due to the expansion of space. For distant galaxies this is the more dominant effect.

I think we're answering two different questions.
I didn't mean to imply that they weren't both occurring. Only that they were two distinct, separate ideas. My point is that the way Andromeda is moving towards the Milky Way has to deal with normal gravitational forces.
It is simply overcoming the effect of the expansion of space.
In this manner (normal gravitational forces), some galaxies are moving apart, and some are moving towards each other.I do not know if "the effect of the expansion of space" is considered "a force" or not. Can it be measured in Newtons? Because of that... I don't know if I can talk about it as "the force of the expansion of space."It's not really a force, but just more space expanding.
Or is it "a force"?
Since there's more space... you need "a force" to overcome it...Or do you simply compare rates?
That is, space expansion obviously has it's own rate-of-expansion (although it's difficult to measure it precisely).
And that is simply compared to whatever forces are causing the rate of relative motion (velocity) through space?
Then it's just a matter of adding/subtracting the two rates of motion to see which one is "dominant"?