December 3rd, 2013, 02:33 PM
We seem to discover somthing new every month on our little planet Earth.
But how with the vastness of space can we see light from 13 billion light years.
If all we see is a spec in a very powerfull telescope, Why is it,that the photons are not absorberd over such a distance
E.G Dust asteroids planets stars is it realistic to asume, over that the vast distance it hits nothing to get to us on Earth.
The universe is mostly empty space, so most photons don't get absorbed.
For comparison, if we were to take the entire mass of the Solar system and spread it out evenly so that it filled a spherical volume enclosed by Pluto's orbit, it would only have a density of ~1.3x10^12 atoms per cubic cm.
Now this might seem like a lot, but it is still considered a high vacuum. And this is magnitudes greater than the density of interstellar space, which in turn is ~1000 times more dense than intergalactic space.
Look at it this way, a 13 billion light year long 1 tube with a 1 square cm cross section would only contain ~20 grams of material. A similar tube of dry air at standard temp and pressure and containing the same amount of mass would only be ~ 290 meters (less than 1/5 mile) long. We can very easily see things through that distance of dry air. Or put another way, there is more material between us and the top of the atmosphere than there is in all the rest of the distance to a galaxy 13 billion light years away.
also gravatational lensing effect causes light to bend around massive objects ,so maybe light just goes around things to get to our little spot in the universe ? and its not just visible light but from infrared to uv ,xray even gamma very powerful.just trying to convince myself
Very informative indeed!Originally Posted by Janus
December 12th, 2013, 08:54 AM
just my imagination. It is considered that the galaxy from where the light is coming, is the first galaxy of the Universe. May be, even if there is any blocker, it might have come after the light passed through it. Now it is impossible to know if there is a blocker inbetween, But it is proved that there was no blocker of it to stop it in the history. everything is interesting.
Last edited by BlindBoy; December 12th, 2013 at 08:57 AM. Reason: Spelling error
I am still trying to figure out how 2 objects got 13 billion light years away from each other. The speed of light is roughly 670 million mph, earth might be hurling through the universe at 2 to 3 million mph and the same, roughly, should apply to the other objects giving off the light... So, how did they get 13 billion light years apart ?
At the speed of 2 million mph through the universe it would take earth 4.3 trillion years to travel 13 billion light years away from an object.
Last edited by gonzales56; December 15th, 2013 at 02:04 AM.
Remember that is just the observable universe. There are (presumably) objects even further away.
And, that would be objects at the edge of our observable universe; there are also objects in the opposite direction, which are twice as far apart.
Also, they were 13 billion light light years away when they emitted the light but are now more like 40-something light years away (I think).
(Actually, I don't think we have actually observed any objects quite that distance yet.)
They are not limited to such humble speeds because they are not travelling through space in the same way as the Earth is. Instead, the space in between is increasing.The speed of light is roughly 670 million mph, earth might be hurling through the universe at 2 to 3 million mph and the same, roughly, should apply to the other objects giving off the light... So, how did they get 13 billion light years apart ?
Consider a number of galaxies separated by the same distance (far enough apart that the expansion of space is significant and the same between all of them).
At time 0, they are 1 unit apart:
A.B.C.D.E.F
After some time they are 2 units apart:
A..B..C..D..E..F
After the same time again, they are 3 units apart:
A...B...C...D...E...F
And so on:
A....B....C....D....E....F
Now, if we look at the distance between B and C, for example, it increases by 1 at every time step. But the distance between B and D increases by 2 at every step. So the distance between B and D is increasing twice as fast as the distance between B and C; i.e. the speed of separation is twice as great.
Choose any pairs of galaxies and you will see that apparent the speed of separation is proportional to the distance between them. Take two objects far enough apart and the speed of separation will be greater than the sped of light. (But that is OK, because the speed of light limit is a local thing, whereas these objects are in different frames of reference.)
I do not know what the evidence is concerning the idea that objects move relatively slow and it is newly created space/distance between objects that creates most of the space/distance between objects.
Where does this occur?
How is the newly created space/distance between objects created?
If new space/distance is being created by space/distance itself, and not by the motion or movement of objects, couldnt space/distance also just vanish and make objects smash into each other?
It is a combination of general relativity (and all the evidence for that), which provides the model for the universe, plus all the evidence for the big bang theory (which confirmed the predictions of GR).
I'm not sure "created" is the best word; space isn't "stuff". It is just a change in the "metric" (the way distance is defined) that changes over time.How is the newly created space/distance between objects created?
It could. GR just says that a stable universe is implausible (it would require things to be incredibly finely balanced). It used to be thought that expansion would slow and eventually reverse but the recent discovery that expansion appears to be accelerating seems to put the kibosh on that.If new space/distance is being created by space/distance itself, and not by the motion or movement of objects, couldnt space/distance also just vanish and make objects smash into each other?
I get the idea that the universe is not stable, what i dont get is how two galaxies in the universe can be 6 trillion miles x 13 billion miles away from each other if the universe is only 13 billion years old. I apologize for my ignorance.
It is worse than that. The furthest objects we could see are now (as much as that can be defined) over 46 billion light years away. So there are objects in the observable universe that are 93 billion light years apart.
This might help: Observable universe - Wikipedia, the free encyclopedia
can we travel ON light to other galaxies
No.
Unfortunately it does not help me. I just cannot and do not understand how those distances are factual. Lets say you and I travel at the speed of light towards this galaxy that is estimated to be 13 billion light years away, ok? We will travel less than 13 billion light years and arrive at our destination. Those on earth observing us (the same way they look at and calculate distance and speed now) on our journey would say we travelled faster than the speed of light and thats why we got there sooner but, that would not be the case. Right? In my mind, hubbles law is irrelevant when something or someone actually begins the journey towards a distant object because the something or someone travelling those "calculated" distances will appear to speed up, when they have not, and arrive much sooner than calculated.
Right or wrong? The further away something is the faster it seems to be travelling? The further we got from earth the faster we too would appear to be travelling, even though we are not? Travelling away from earth and constantly getting closer to this object supposedly 13 billion light years away from earth would also cause that object to appear to slow down more and more, correct? In my mind the calculations of actual distance are wrong.
Well if you had a clue it might help.
What?and arrive much sooner than calculated.
Maybe you can understand this. Object that are claimed to be 40 billion light years away from earth surely travelled that distance in well under 40 billion years.Well if you had a clue it might help.What?and arrive much sooner than calculated.
Again, traveling at the speed of light, what you would call 30 billion light years away from earth, might not even take something traveling at the speed of light 100 million light years to accomplish (the math would have to be done to find out the actual time for something to cover the distance).
Last edited by gonzales56; December 21st, 2013 at 04:17 AM.
Nope.Object that are claimed to be 40 billion light years away from earth surely travelled that distance in well under 40 billion years.
They didn't travel all that distance: the space between them expanded.
If you travel 13 billion light years at the speed of light it will take 13 billion years.
Lets stick with reality and say, "near the speed of light". Yes, we will see the distance as less and so it will take us less than 13 billion years. (Ignoring the fact that the galaxy is actually receding from us.)
No, they would see us travelling at near the speed of light and say it took us just over 13 billion years. (Again, ignoring the fact that the destination is moving away.)Those on earth observing us (the same way they look at and calculate distance and speed now) on our journey would say we travelled faster than the speed of light and thats why we got there sooner but, that would not be the case. Right?
However, they will know that our time is dilated (relative to them) and so they will agree on how much time we think it took.
No, because the calculations are all done in the same frame of reference. Hubble's measurements were all done in the frame of reference of the Earth. Nowadays, something called "co-moving coordinates" are used.In my mind, hubbles law is irrelevant when something or someone actually begins the journey towards a distant object because the something or someone travelling those "calculated" distances will appear to speed up, when they have not, and arrive much sooner than calculated.
We never use the distances/times of the travelling object. Especially true in the case of light as that is not a valid frame of reference.
Wrong, in the sense that distance doesn't automatically make something appear to travel faster.Right or wrong? The further away something is the faster it seems to be travelling?
Right, in the sense that, on cosmological scales, the changing scale of distance between objects causes them to separate at a rate dependent on distance. This has nothing to do with the relativistic effects above.
No.The further we got from earth the faster we too would appear to be travelling, even though we are not? Travelling away from earth and constantly getting closer to this object supposedly 13 billion light years away from earth would also cause that object to appear to slow down more and more, correct?
We don't measure distance by travelling to those stars, so the relativistic issues you raise above are largely irrelevant. Also, the entire model is based on the theory of (general) relativity and so any other effects that are relevant are included automatically.In my mind the calculations of actual distance are wrong.
That is explained by post 8; objects far enough apart will be separating at more than light speed.
Dont matter if something travels at the speed of light or near the speed of light. It would not take it 13 billion years to reach that galaxy. It would do it sooner.
That galaxy, travelling at perhaps 2 million mph combined with the rate of expansion, got that far from earth in far less time than 13 billion years, and something traveling at the speed of light or near the speed of light + expansion would arrive at that galaxy in far less than 13 billion years from now, right?
Again, correct me if i am wrong but, if the expansion between us and that galaxy was greater than the speed of light then we would not be seeing it. Correct? Near the speed of light or the speed of light, surely then, can overcome the speed of expansion between earth and that galaxing, and as it got closer and closer the speed of expansion would continually be reduced. How is this wrong?
Last edited by gonzales56; December 21st, 2013 at 05:04 AM.
Why do you think this?
No.That galaxy, travelling at perhaps 2 million mph combined with the rate of expansion, got that far from earth in far less time than 13 billion years, and something traveling at the speed of light or near the speed of light + expansion would arrive at that galaxy in far less than 13 billion years from now, right?
You're wrong.Again, correct me if i am wrong but, if the expansion between us and that galaxy was greater than the speed of light then we would not be seeing it. Correct? Near the speed of light or the speed of light, surely then, can overcome the speed of expansion between earth and that galaxing, and as it got closer and closer the speed of expansion would continually be reduced. How is this wrong?
I have no idea what you mean by "overcome the speed of expansion".
We still have to travel IN space.
If we're travelling in space and that space is expanding then we travel WITH that expanding space: regardless whatever the final distance is (at the end of the journey) because of that expansion we've still only travelled at light speed.
However long light takes to cover the distance is exactly how long it would take us if we travel at light speed.
Ignoring the complication of expansion for the moment, if there is an object at 13 billion light years and you travel at (or nearly at) the speed of light, then it will take 13 billion light years (or slightly more) to get there. That is what "light year" means.
Once you factor in expansion, then it will always take you more time. As you head towards that distant galaxy, the distance between you and it. If it is far enough away, that will be happening faster than you can cover the distance and so you will never reach it.That galaxy, travelling at perhaps 2 million mph combined with the rate of expansion, got that far from earth in far less time than 13 billion years, and something traveling at the speed of light or near the speed of light + expansion would arrive at that galaxy in far less than 13 billion years from now, right?
I am not clear on the details at the extremes, but I believe there are objects which we can (in principle) see which are moving away faster than the speed of light. But when the light was emitted, they were not.Again, correct me if i am wrong but, if the expansion between us and that galaxy was greater than the speed of light then we would not be seeing it. Correct?
This might answer some questions in more detail: Frequently Asked Questions in Cosmology
And if you want to learn more: Ned Wright's Cosmology Tutorial - Part 1
Maybe i can word my questions different.. The universe is 13 billion years old right? The speed of light is the speed limit correct? Minus expansion, light should be no further that 26 billion light years across the universe, right? Galaxies, only travelling at a fraction of the speed light, minus expansion, would only be in the millions of light years apart from one and another? Any expansion in space between objects greater that the speed of light would not allow that light to reach each other. The only way, in my mind, that light reached earth from an object 40 billion light years away is if that galaxy is not 40 billion light years away.
If you slap 40 billion light years of new space between objects, and only give light a feww billion years to travel it, it is not going to cover that space. It will not hit earth. How is this wrong?
That is a "local" limit for things in the same frame of reference. It doesn't apply on cosmological scales where the objects are not moving relative to one another in the same frame of reference but are in different frames of reference with different scale factors.
A lot of people seem to think there is some sort of contradiction here but there can't be. The "speed limit" comes from the theory of relativity and the expansion of space comes from the theory of relativity. It is a single theory. These are two different results of the theory. Because the theory is internally consistent (which it must be because it is a "theory") then there cannot be a conflict here.
See the above FAQ or tutorial for more. Or John Baez's: gr
Free Christmas trivia: Joan Baez is his cousin.
The speed of light in each "frame" is still the same in each "frame" regardless of distance or our perception of distance from earth. Light, like Us and our galaxy, does not expand with the space between "frames". Again, if 40 billion light years of new space is created in a billion years between us and and the galaxies nearest to us, that light would be cut off from us and it would then take 40 billion years to reach Us. We would no longer see those galaxies. How is this wrong?That is a "local" limit for things in the same frame of reference. It doesn't apply on cosmological scales where the objects are not moving relative to one another in the same frame of reference but are in different frames of reference with different scale factors.A lot of people seem to think there is some sort of contradiction here but there can't be. The "speed limit" comes from the theory of relativity and the expansion of space comes from the theory of relativity. It is a single theory. These are two different results of the theory. Because the theory is internally consistent (which it must be because it is a "theory") then there cannot be a conflict here.See the above FAQ or tutorial for more. Or John Baez's: grFree Christmas trivia: Joan Baez is his cousin.
Yes. There is a point beyond which we could never see anything because, as you say, space is expanding faster than the light can traverse the distance. That is why there is a "horizon" or edge of the observable universe.
That distance doesn't correspond to the distance at which things are receding at the speed of light (for reasons I haven't fully got my head round, myself).
Are you saying or suggesting that the galaxy they are looking at, the image itself, is not 13 billion light years away, it is much closer than that and they are simply using calculations to say that the actual galaxy in the image, not the image, is now 13 billion light years away?
Not the location or distance of the observable universe but rather where these things are now?
I don't think I am saying that. But I'm not really sure what you are asking. which galaxy?
If we see a galaxy that it took 13 billion light years for the light to reach us, then it was 4 (???) billion light years away when that light was emitted and is now ~46 billion light years away.
But you probably need someone who understands this stuff better than me to explain it...
[QUOTE=Strange;505771]No. When astronomers say that we see an object in space X number of light years away, they mean it was that far away WHEN THE LIGHT WE SEE TODAY LEFT IT. (caps only for emphasis) That particular object is much further away now. Moreover, this does not include the additional distance light had to cover that comes from the expansion of the Universe (don't even ask how fast the Universe is expanding. In my research, no one knows)The problem you are facing is, I believe, common. You cannot use the everyday experiences you are used to in attempt to understand cosmological concepts. These concepts seem to defy what most people think of as common sense. For example, when most people think of an explosion, they think of a "ground zero" where the explosion occurred and the effects that radiate outwards from it. Now, if you try to use that logic with the Big Bang and assume there is a center to the Universe and ask questions like "where is it?" or "what direction does it lie?", you'll quickly find yourself lost. There is no center to the Universe. It's one of those things like 2 + 2 = 4. Just accept it or be prepared to spend a few years learning higher Cosmology/Astro Physics. In addition, space is *curved* which adds a whole new series of issues to understand. Note that this is not the "dimples" in space/time ascribed to mass by Einstein's Theory of General Relativity; space itself is actually curved. No, I don't completely understand it either
Cheers!
Michael
sir ir r aj asked:
can we travel ON light to other galaxies
That's not exactly true, it depends on what you mean by "on". It is conceivable that we could use high powered lasers to propel craft at less than light speed to other stars, and I suppose, given the right set of engineering circumstances, such a system could be used (in multiple sets of series) to propel a craft to another galaxy, but even if we could achieve velocities that approached light speed, it would take millions of years at the very least.
If, on the other hand, you are asking if we could literally *ride* a beam of light, then no, not at the current or any forseeable future level of technology. Nice thought though
Michael
How can light leave from something in the universe 45 billion years ago? That light, IMO is but a few billion years old, not 10's of billions of years old (if the universe is 13 billion years old).
Did anyone say that? The light that has taken 13 billion years to reach us, is from objects that are now ~46 billion light years away. The light they are emitting now, will not reach us for hundreds of billions of light years (if ever).
It is all relative, right? Calculating time, and thus distance/space, based on our perspective, at our speed through space, just seems off to me. For 1 second just imagine that you are traveling at the speed of light and I am sitting on earth. At the speed you are moving, what happens to time?Did anyone say that? The light that has taken 13 billion years to reach us, is from objects that are now ~46 billion light years away. The light they are emitting now, will not reach us for hundreds of billions of light years (if ever).
Maybe I can ask like this... Time dilation, correct? Space-time, right? Any change in time would change ones perceived/calculated distance would it not? A change in time is also a change in space?
Everyone has to agree on the speed of light.....? What has to change in order for everyone to agree on the speed of light is space-time and thus distance, correct? The 13 billion light years away number is a time and distance based on our motion. Change the motion and time and distance changes with it... ?
It seems to me that if someone was looking at light and calculating how far that light has travelled and for how long, they are doing so based soley on their relative motion and not universal fact. It seems to me that if I was moving much faster than them, while looking at the same light, and then calculated its distance and time, my calculation in both time and distance would be much shorter than the other person who's speed was much slower than mine.
Last edited by gonzales56; January 2nd, 2014 at 04:55 AM.
no it wouldn't. because c is c to all observers, no matter what speed.
Two important points here. The questions you raise are based on the effects of relativity. This is also the basis of the big bang model and so any such effects are, by definition taken account of. Also, in order to make these age / distance comparisons throughout the universe, a consistent frame of reference is used ("co-moving coordinates").
Speed of light is the same but, the different speeds of the observers, observing the same light, produces different calculations of distances and time the light has travelled. C is constant, distance and time is not, they change with speed.
The reference frame is only ours.. Change the speed at which we move and the time and distance numbers will change as well. Remember, regardless of how fast something is traveling, all observers at all speeds must agree that the speed if light is the same. The only way this occurs is because they will not agree on the time or distance the light has travelled. In our frame that galaxy appears to be 13 billion light years away, however, increase our speed and that same galaxy will be less than 13 billion light years away.Two important points here. The questions you raise are based on the effects of relativity. This is also the basis of the big bang model and so any such effects are, by definition taken account of. Also, in order to make these age / distance comparisons throughout the universe, a consistent frame of reference is used ("co-moving coordinates").
Yes. So? We know exactly how much a change of reference frame would change the measurements and the required calculations. We know we are not stationary with respect to co-moving coordinates and that is taken into account. If we were moving at a different speed, then the observations would be slightly different and so would the corresponding calculations. This is all part of the model.
I'm not sure what your point is. It seems to be, "the calculations must be complicated and I don't understand how it is done." All I can suggest is that you work through the tutorial linked earlier. Or ask some more specific questions.
ifthe moment a light beam hits earth, which traveled 2 lys to reach us, a spaceship would pass earth at c: it would also calculate the source to be 2 lys away.Speed of light is the same but, the different speeds of the observers, observing the same light, produces different calculations of distances and time the light has travelled. C is constant, distance and time is not, they change with speed.
Not true. The spaceship, travelling near (*) the speed of light, would calculate the distance to be less.
(*) Just to make it possible to calculate the answer.
We would scream and shout that it was 2lys away but, that space ship would not. At .99c the people would see the light as being just 2 light days away. This is time dilation, special relativity.ifthe moment a light beam hits earth, which traveled 2 lys to reach us, a spaceship would pass earth at c: it would also calculate the source to be 2 lys away.Speed of light is the same but, the different speeds of the observers, observing the same light, produces different calculations of distances and time the light has travelled. C is constant, distance and time is not, they change with speed.
If that spaceship then travels to that light source, their clock will show it took 2 days. If they turn around and head back to earth, it will take another 2 days. When they arrived back on earth, we will have had 4 years pass. I think they call this the twin paradox.
Last edited by gonzales56; January 2nd, 2014 at 08:23 PM.
The point is that our observations of the speed of light and space-time is only relative to our motion and gravity. Change the motion and gravity and space-time changes. 2 light years to Us on earth is a distance that will not be 2 light years away to an observer at a different speed and gravitational influence.
The spaceship would measure the source as being 1.7 light months away. (Where did you get 2 light days from?)
Yes. So what?
I was being lazy and took it off a Hawkins science channel programThe spaceship would measure the source as being 1.7 light months away. (Where did you get 2 light days from?)
For 2 light years to be compressed to 2 light days, the spaceship would need to be travelling at 0.999996c !
Thank You Strange....
Probably much of what we think is right today will be laughed at in a hundred years.
This just confirms my reasons for putting you on ignore.
Bloody Hell a Jim Colyer post that isn't crap song lyrics (just crap).
Like we are laughing at the theories of 100 years ago... relativity, quantum theory, etc?
Hmmm. Maybe not, then.
ok, now i'm confused.
so that light took 2 lyrs to reach earth hitting the passing spaceship also. but it wouldn't take the spaceship 2 lyrs to get to its source traveling only .9c?
As measured by observers on Earth, it would take the the spaceship 2.2 years to get there. But for the people on the ship, only 1.7 months would pass.
This video may help
Didn't you hear the news? Stars are connected by light pillars :P~
*runs away*
oh you're talking about observersAs measured by observers on Earth, it would take the the spaceship 2.2 years to get there. But for the people on the ship, only 1.7 months would pass.
What else is there?oh you're talking about observersAs measured by observers on Earth, it would take the the spaceship 2.2 years to get there. But for the people on the ship, only 1.7 months would pass.
i shouldn't reply pre-coffein input lol.What else is there?oh you're talking about observersAs measured by observers on Earth, it would take the the spaceship 2.2 years to get there. But for the people on the ship, only 1.7 months would pass.
What Mathman said.
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