Is Krauss looking at this right?

[zapatos]

And it is assuming that such scientists will be operatiing in similar fashion to how humans operate, with the same constraints, the same abilities, the same time and size scale, and the same basic way of looking at the universe, that human's have.

This is your assumption, not his. Don't lay that assumption on his doorstep.

 

That Krauss can care about such a view...

What do you mean 'care' about such a view. He looked at current evidence and followed it forward, just as others have followed it backward to the big bang. You are criticizing him for looking at evidence and using his training to make a prediction; just like all scientists do. Why pick on him and not every other scientist?

 

And to consider he is RIGHT about it, has just about as much validity or purpose, or value, as considering that the Earth is balanced on the back of a Turtle.

Bullshit. Now you are suggesting he is making things up and are questioning his integrity. Or that he has no intelligence at all. He made the prediction based on evidence. Where is the evidence of your Turtle?

 

He is concerned over absolutely nothing real.

He is showing no concern over anything at all that I can see. He is simply telling us what he thinks. I saw no hint of fear, concern, or anything else negative. If anything he seemed to be showing amazement at the universe.

 

If we are to go on flights of fancy, given half a trillion years, there could also be the possibiliy that consciousness the size of star systems could develop, and they could have memories that last a billion years, and they may have the patience of an Ent, or more, and be able to wait for a signal the wavelength of a galaxy to arrive.

The signal will never arrive, no matter how long they wait. If the signal is travelling at c, it will never catch up to the galaxy whose distance is increasing at a rate greater than c.

 

Why make any assumptions at all, about what they will be able to know about, constraining them to the models held in the minds of human Earthlings, when the universe was just a babe, only 13.7 billion years old?

Why do you care what his motivation is? He is a scientist doing science, and trying to convey his wonder of the universe to those like me who could not figure it out on my own. He follows the evidence to its probable conclusion, knowing full well that he could be wrong.

 

This particular post of yours only confirms in my mind that for some reason you either have a bias against Krauss, or you have no idea how scientists use evidence to make predictions.

[Spyman]

I am viewing him as a proxy for people who believe their model of the universe is as good as, or superior to, the universe itself. I think this to be a delusion of sorts.

I am sorry Tar but you are the delusioned one, neither Krauss, any other professional cosmologists, scientist in general or any one else in this thread are claiming that models are superior to nature or that we can predict the future exactly with one hundred percent certainty.

 

 

While people like you and me can have problems trying to understand math, diagrams and advanced models on our free time as amateur cosmologists, the professionals knows about these things, models are tested and compared against reality, models that fails gets discarded. If I drop one hundred apples, I can guess the next apple will fall to the ground too, after some billion apples I will be pretty certain what will happen to the next one.

 

We are currently observing the Universe in all directions, everywhere we look and how far back we look it behaves in a similar uniform fashion. From redshifts they can determine how fast objects where receding from us when they emitted the light we measure and with the help of standard candles like certain supernovas they can determine how long time it took for this light to reach us. When they use this knowledge together they can make a model of how the Universe has evolved the last 13 billion years, this model is far from being a fantasy about a Turtle carrying Earth on its shell.

 

 

Imagine a man is who is running towards the edge of the roof on a high building, people are telling him to stop, that he is going to get hurt, but he is determined to make the leap of faith. He covers his ears and eyes trying to resist their attempts to save him and shouts vigorously to them that Newton is preposterous believing his model of gravity is superior to nature. Newton is concerned over absolutely nothing real, he tells them, that if we are to go on his flights of fancy, there could even be the possibiliy that Ents will save me. Why should I be scared?

 

You can jump all you want, but I am concerned enough to take the stairs back down.

Edited October 8, 2012 by Spyman

[michel123456]

I am sorry Tar but you are the delusioned one, neither Krauss, any other professional cosmologists, scientist in general or any one else in this thread are claiming that models are superior to nature or that we can predict the future exactly with one hundred percent certainty.

 

 

While people like you and me can have problems trying to understand math, diagrams and advanced models on our free time as amateur cosmologists, the professionals knows about these things, models are tested and compared against reality, models that fails gets discarded. If I drop one hundred apples, I can guess the next apple will fall to the ground too, after some billion apples I will be pretty certain what will happen to the next one.

 

We are currently observing the Universe in all directions, everywhere we look and how far back we look it behaves in a similar uniform fashion. From redshifts they can determine how fast objects where receding from us when they emitted the light we measure and with the help of standard candles like certain supernovas they can determine how long time it took for this light to reach us. When they use this knowledge together they can make a model of how the Universe has evolved the last 13 billion years, this model is far from being a fantasy about a Turtle carrying Earth on its shell.

 

 

Imagine a man is who is running towards the edge of the roof on a high building, people are telling him to stop, that he is going to get hurt, but he is determined to make the leap of faith. He covers his ears and eyes trying to resist their attempts to save him and shouts vigorously to them that Newton is preposterous believing his model of gravity is superior to nature. Newton is concerned over absolutely nothing real, he tells them, that if we are to go on his flights of fancy, there could even be the possibiliy that Ents will save me. Why should I be scared?

 

You can jump all you want, but I am concerned enough to take the stairs back down.

 

Taking your example, what Krauss says is that in a few billion years, a man in the future will observe only the roof because the ground floor will have get out of observation, and that around the building only void will exist. Krauss says also that the man in the future will be wrong, and that we are right.

[zapatos]

Krauss says also that the man in the future will be wrong, and that we are right.

Not quite. He is saying that the man in the future will be wrong about some particular aspect of the universe. Similarly, if some intelligent life existed 13 billion years ago, I am quite sure they would understand something about the universe that we are incorrectly speculating about today. You haven't really explained why you have such a problem with that concept.

[Spyman]

Taking your example, what Krauss says is that in a few billion years, a man in the future will observe only the roof because the ground floor will have get out of observation, and that around the building only void will exist. Krauss says also that the man in the future will be wrong, and that we are right.

First of all, you are completely missing the point of my example and I can't even understand what your example is trying to show.

 

Secondly, Krauss is NOT talking about a itsy bitsy tiny winy *few* billion years, he speaks about one hundred billion years, which is more than seven times the current age of the Universe, that's a whole lot more than a few, even in cosmological timescales.

 

Further more, I think that in the context, Krauss is trying to say that future civilizations are unable to use their telescopes and observations of the sky, to peer back in time and see distant galaxies like we currently are. All traces of the Big Bang, such evidence that we currently can observe, will by then be gone forever. They will view a different universe than us and will therefore make other conclusions based on their observations.

 

Like zapatos, I would like to know why you can't accept that different information will cause different conclusions about the same event?

[michel123456]

I can't believe you guys.

 

I think my concept is quite clear. I thought it was evident (i was wrong about that)

 

My concept is that there is no reason to suppose that we are living a "special" period of the universe. The other concept (yours) that people in the far future will observe a different universe, and take wrong conclusions from it, seems complete bogus to me. Not to say ridiculous.

 

At the moment we are speaking about a Spacetime continuum, what we ought to consider logical to space (the cosmological principle) must also count for time.

It looks to me evident that an E,T, on another star of another Galaxy, anywhere else, at any time, should observe something roughly the same as what we are observing from here today. That means an E.T. billions of years in the past, and an E.T. (or H.B.) billions of year in the future. That's what I call the extended cosmological principle.

 

The other cosmological principle, the one we all agree upon, assembled with current cosmology, literally states that only the observers at the same cosmological time with us are observing the same universe than we do. That is in some "cosmological present earth time". Following current cosmology, all other observer should observe some other universe, younger or older

 

So, a standard cosmologist should correct the cosmological principle by stating that 'Viewed on a sufficiently large scale, THAT BELONG TO EARTH PRESENT TIME" (capital letters added by me). See wiki

 

If you are a fervent supporter of the cosmological principle (as i am), you don't want to add anything to it. And if you add nothing to the cosmological principle, you must reach the conclusion that "the properties of the Universe are the same for all observers", either left, right, close or far away, yesterday and tomorrow.

[zapatos]

If you are a fervent supporter of the cosmological principle (as i am), you don't want to add anything to it. And if you add nothing to the cosmological principle, you must reach the conclusion that "the properties of the Universe are the same for all observers", either left, right, close or far away, yesterday and tomorrow.

Yes, the properties of the Universe are the same for all observers. So what? Being able to see an astronomical entity one day and not another did not change any 'properties of the universe'.

 

Someone could see what you did yesterday, but now I cannot see what you did yesterday. Does that mean a property of the universe changed?

 

How is that different than I can see a galaxy today and someone in 100 billion years cannot see it?

[tar]

All,

 

I am operating on the TAR model, and that is the only one I am capable of considering. It can and has been modified over the years, by evidence and logic provided by others. I can focus on, and evaluate various aspects of it to consider if something is or is not the case. When my conclusions differ from the conclusions of others, it is difficult to drop my notions, in favor of theirs. However I generally give particular others, or individual others, the benefit of the doubt and demand of myself that I either accept as true, that which they are telling me, and modify my model appropriately, or find an objective view from which both my model and theirs are modeling the same reality.

 

In this pursuit, I am assuming there is a consistent reality, that is similtaneously being modeled by both me and the other.

 

When both I and the other, understand the same thing to be the case, take a distant galaxy for instance, we envision that galaxy as having to be like ours, or similar in nature, and as we can concieve of the Milky Way as one spiral galaxy, that we can view all at once, in a simulated graphic or an artists rendering, we can take the same type unit and place it out, billions of lys away, and consider it truely to be out there, right now, doing something we will not see it do for 10s of billions of years, or in the case of a very distant one of these galaxy units, not EVER see what it is doing now.

 

But this envisionment leaves out an important consideration. We do not see anything immediately. We see it after the photons make the trip, hit the back of our eye, form signals that are then interpreted by our brains and fed into our model.

We have to make the interpretation that there is a one to one correspondence between the object in question, and our internal model of it. We think of the thing as being outside our bodies and brain, because it is. We have learned how to interpret this one to one correspondence. It is actual and real.

 

You and I both, have a model of the Statue of Liberty, standing in NY harbor. Even though we do not currently see it. It only exists once in reality. That is, there is only one instance of the Statue of Liberty, and it always stands in NY harbor.

 

How many instances of this distant galaxy must we consider to currently be the case? There is only one instance of it. And it is always spiraling in its location in space surrounded by its neighbors.

 

If we can see it now, we know its there. Right where we figure it to be. If space has been, and will be expanding, we will see it standing there tomorrow at a slightly diminished power level, and at slightly redder wavelengths. Less photons tomorrow, than arrived today, and longer wavelengths.

 

A long time ago, that galaxy was "out of view" of a human eye. We had to construct huge eyes, huge lenses to focus the sparse photons on a CCD and interpret the signals and piece the data together over hours and days, to determine that that Galaxy must be spiraling out there, now. It exists in our universe. One instance only. We see it now, and I contend a future race will be able to peice together its existence so that they too will know it is spiraling out there, in the massive way it is.

 

Regards, TAR2

 

Its photons are currently on their way here, and do not have a way to disappear. Longer wavelengths tomorrow, fewer photons, sure. But disappear? How could a galaxy disappear.

 

We have reached farther and farther out into our universe, increased our reach, faster than even the expansion can carry it away from us. I would grant future scientists abilities far beyond our own.

 

Especially if we were to leave them a record of what we have noticed.

Edited October 9, 2012 by tar

[zapatos]

But this envisionment leaves out an important consideration. We do not see anything immediately. We see it after the photons make the trip, hit the back of our eye, form signals that are then interpreted by our brains and fed into our model.

Right. We see it after the photon makes it to us.

 

...and I contend a future race will be able to peice together its existence so that they too will know it is spiraling out there, in the massive way it is.

How will they piece it together if the photon never reaches them? If the photon travels at c, and the distance between the galaxies is increasing at a rate greater than c, how will the photon ever hit the back of their eye?

 

We have reached farther and farther out into our universe, increased our reach, faster than even the expansion can carry it away from us.

That is incorrect. We are not 'reaching' anywhere. The photon still needs to come to us, and it cannot come to us faster than c.

Edited October 9, 2012 by zapatos

[tar]

 

How will they piece it together if the photon never reaches them? If the photon travels at c, and the distance between the galaxies is increasing at a rate greater than c, how will the photon ever hit the back of their eye?

 

Zapatos,

 

Well here is exactly the point I am trying to make. The object is not what we see. It is the object's photons, informing us of its existence that we see, here and now. Whether the galaxy itself is now a black hole, invisible to everywhere, even its neighbors, is not critical or even pertinent to what we see. We see what it was at an earlier time, and that informs us as well, of its distance from us.

 

Starting now, we watch the young distant galaxy. It gets smaller, ages more and more slowly, its photons get sparser, and more redshifted. If it mathematically must be, currently moving away from us, faster than the speed of light, but we currently see it, what it is doing now, is not important. That information might never get to here. But every moment of that galaxy's existence, between its age now, and its age when it's recessional speed reaches C, must be on its way here, and we will see the appropriate photons coming in, when we look in its direction. If now we see it at a Z of 5, we will see it age only a year, in five years? As it's redshift increases over the eons, it will age slower and slower, never reaching the age of 13.7 billion years in our 100billion year old eyes. When we are 500billion years old, it MUST look younger than its age when it's recessional speed exceeded C. Either that, or we would see it older than 13.7billion years old, which physics is predicting is not going to happen. The light stream between us, and that galaxy has no way to break. We are connected to that galaxy in this fashion. Forever. 5 or 10 billion years worth of ants are currently on their way here, on that rubber band. And there is no "last" ant, to arrive. There is always the next one, just a stretched wavelength behind.

 

Regards, TAR2

[zapatos]

...every moment of that galaxy's existence, between its age now, and its age when it's recessional speed reaches C, must be on its way here, and we will see the appropriate photons coming in, when we look in its direction.

Agreed.

 

 

...When we are 500billion years old, it MUST look younger than its age when it's recessional speed exceeded C.

Everything in the universe looks younger than it 'actually' is, since some amount of time, whether long or short, passes between the time the photon leaves the object and the time it arrives at your eye.

 

The light stream between us, and that galaxy has no way to break. We are connected to that galaxy in this fashion.

You'll have to explain that in terms of physics. But it brings me to my question, which I would appreciate if you would answer in a yes/no fashion to start even if you give more explanation after.

 

Do you believe that a photon emitted from a star, whose recessional speed exceeds c, will ever reach our eye?

 

And as a follow up, if you answer yes to the above question:

Did the photon mentioned above travel at c?

 

And as a follow up, if you answer yes to the above question:

How did the photon travelling at c catch up to an object whose recessional speed exceeds c?

Edited October 10, 2012 by zapatos

[tar]

Zapatos,

 

Yes I believe those things.

 

But it is because I believe them, and because we see the galaxy now, that I am sure we will always see the galaxy, when we look in that direction. It can never run out of photons, as long as it exists. And those photos, that started out in our direction, have only essentially three attributes, relative to us. 1. They are on their way to us, 2. They are now reaching us, 3. They missed us on the way by and are on their way to some area of space behind us (should we be facing the galaxy in question). There is not an age we can reach where these three conditions are not still valid.

 

Regards, TAR2

 

fourth condition. They get absorbed, and inform some other entity between us and the galaxy, or some entity behind us.

Which allows for the possibility that that entity might re-emit a photon, analogous to the original.

[zapatos]

Zapatos,

 

Yes I believe those things.

 

But it is because I believe them, and because we see the galaxy now, that I am sure we will always see the galaxy, when we look in that direction. It can never run out of photons, as long as it exists. And those photos, that started out in our direction, have only essentially three attributes, relative to us. 1. They are on their way to us, 2. They are now reaching us, 3. They missed us on the way by and are on their way to some area of space behind us (should we be facing the galaxy in question). There is not an age we can reach where these three conditions are not still valid.

 

Regards, TAR2

 

fourth condition. They get absorbed, and inform some other entity between us and the galaxy, or some entity behind us.

Which allows for the possibility that that entity might re-emit a photon, analogous to the original.

Ok.

 

You believe a photon will travel at c, and that a photon can reach an object whose recessional speed exceeds c.

 

But I missed the answer to the last question.

 

How did the photon travelling at c catch up to an object whose recessional speed exceeds c?

 

Similarly, how will I catch up to my wife if I am running at 10mph, and she is driving away at 20mph?

[michel123456]

 

(...)

Similarly, how will I catch up to my wife if I am running at 10mph, and she is driving away at 20mph?

 

If i understand Tar's idea:

You are not alone running at 10mph. Some billions years ago, some other husband was running away in your wife 's direction, and your wife hasn't reach this husband yet.

 

that is because following the standard model, we were all created at the same time (the Big Bang).

Edited October 10, 2012 by michel123456

[zapatos]

If i understand Tar's idea:

You are not alone running at 10mph. Some billions years ago, some other husband was running away in your wife 's direction, and your wife hasn't reach this husband yet.

 

that is because following the standard model, we were all created at the same time (the Big Bang).

Sometimes I wonder if it is risky starting analogies because of where it can go, but...

 

If this other husband started running toward my wife when she was still accelerating in her car, and he was running at 10mph and the car was only going 5mph, he could catch her. But if she is already going faster than 10mph when I start running, I will never catch her.

 

We didn't all start running toward her at the same time. Some started running when she was travelling slowly, before she realized a bunch of crazed men were chasing her!

[tar]

Zapatos,

 

Your wifes car has a very small speed, compared to the speed you can run. You can run at C. The recessional speed of a galaxy, from ours is how the slowly accelerating speed of your wifes car has eventually exceed C. If you were to leave the house, after she has exceed C, you would not catch her.

But her car itself, is actually standing still, on the road, for the analogy to be more appropriate. In fact she might as well get out of the car, and wait for you, it is the road that is expanding in length, and the distance between her and the house, is increasing faster than the speed of light. I am wondering, under the stationary wife, waiting for you next to her car, whether we should reevaluate the possibilities of you, moving at C, reaching her. The wife and the house, are receeding from each other at greater than C, and the road continues its slow stretch. It is not the speed of the accelerating stretch you need to overcome, as much as the incredible distance between the house and the wife, at the point at which the slow stretch of any peice of the road, has added up to an above C recessional speed of the house to the wife. But each peice of the road is only slowly expanding, compared to your C speed, and you can actually make progress from cobble to cobble. Even though the cobbles are expanding, there is still the same number of them, so to speak, on the road. And from one end of a single cobble to the other, the ends are NOT receeding from each other, at greater than C. At C, you can transit a cobble, even though it keeps taking you slightly longer to transit the next. There is only a finite number of cobbles to transit, so at any length of time it takes to transit a cobble, you eventually should be able to reach your wife.

 

Right?

 

So let me hold in reserve the possibility that I might not agree with the statement that light from a galaxy receeding at plus C can not eventually reach our Milky Way, and put that aside for a moment, as a side question. The actual question does not pertain to what photons that distant galaxy is emitting now, it pertains to the photons it emitted in the 13.7 billion years prior to now.

 

If we can see it now (as sparce and redshifted as it is), that requires that we have been seeing it, since the universe became transparent to us (eternal Milky Way observer types), at that distance. I would imagine that the (three second) moment the universe became transparent to photons, we could see clearly about 600thousand miles out, surrounded by the fog of an untransparent universe. This clearing of the fog, would expand out at the speed of light, as photons released at the clearing reached us. At some point, probably only a few 10s of millions of years, (but let's say 10 billion just to make sure) the first light of this distant galaxy reached the Earth, and from that point on, we have watched it age in close to real time, dilated only by its increasing redshift. That galaxy's actual age, is 13.7billion years old, but we are seeing it much younger than that. We have yet to see it age to 13.7 billion years old. All the photons, from when it was young till now, are on there way here, now, regardless of its current recessional speed, and we will be receiving those photons when they get here.

 

Regards, TAR2

[ACG52]

I would imagine that the (three second) moment the universe became transparent to photons

 

377,000 years, not three seconds.

 

we could see clearly about 600thousand miles out, surrounded by the fog of an untransparent universe.

 

You couldn't see any distance at all. A uniform fog of ions means that photons could barely travel any distance before absorbtion.

 

This clearing of the fog, would expand out at the speed of light, as photons released at the clearing reached us.

 

There was no 'clearing'. It happened everywhere at just about the same time, as the temperature of the universe dropped below a 3000K.

[zapatos]

Zapatos,

 

Your wifes car has a very small speed, compared to the speed you can run. You can run at C. The recessional speed of a galaxy, from ours is how the slowly accelerating speed of your wifes car has eventually exceed C. If you were to leave the house, after she has exceed C, you would not catch her.

But her car itself, is actually standing still, on the road, for the analogy to be more appropriate. In fact she might as well get out of the car, and wait for you, it is the road that is expanding in length, and the distance between her and the house, is increasing faster than the speed of light. I am wondering, under the stationary wife, waiting for you next to her car, whether we should reevaluate the possibilities of you, moving at C, reaching her. The wife and the house, are receeding from each other at greater than C, and the road continues its slow stretch. It is not the speed of the accelerating stretch you need to overcome, as much as the incredible distance between the house and the wife, at the point at which the slow stretch of any peice of the road, has added up to an above C recessional speed of the house to the wife. But each peice of the road is only slowly expanding, compared to your C speed, and you can actually make progress from cobble to cobble. Even though the cobbles are expanding, there is still the same number of them, so to speak, on the road. And from one end of a single cobble to the other, the ends are NOT receeding from each other, at greater than C. At C, you can transit a cobble, even though it keeps taking you slightly longer to transit the next. There is only a finite number of cobbles to transit, so at any length of time it takes to transit a cobble, you eventually should be able to reach your wife.

 

Right?

No. If for every inch of road I traverse, the road grows by two inches, I will never reach my wife. It is that simple.

 

...The actual question does not pertain to what photons that distant galaxy is emitting now, it pertains to the photons it emitted in the 13.7 billion years prior to now.

...All the photons, from when it was young till now, are on there way here, now, regardless of its current recessional speed, and we will be receiving those photons when they get here.

Correct. That is not in question

 

The photons that were emitted prior to the recessional speed exceeding c will reach us.

The photons that are emitted after the recessional speed exceeds c will not reach us.

After the last photon that was emitted prior to the recessional speed exceeding c reaches us, no other photons from that galaxy will reach us. At that point the galaxy will be lost to us.

[michel123456]

No. If for every inch of road I traverse, the road grows by two inches, I will never reach my wife. It is that simple.

 

I don't think it is that simple.

 

When the road grows by 2 inches, it means that there is scale factor of 2. When the scale factor is applied to space, it is applied also to any velocity (because velocity is spce/time), and thus it is applied to C also.

That's why we observe galaxies receding at apparent speed multiple of C.

 

Or:

if the road is 10 inches long, one inch travel is 10% of the road.

 

When suddenly the road extends to 20 inches long (by scaling), then one "scaled-inch" still is 10% of the length, or 2 inches. The important thing is that for the same time, the distance as measured in the new space system (the scaled-space) remains constant: that's the main property of C.

[zapatos]

When the road grows by 2 inches, it means that there is scale factor of 2. When the scale factor is applied to space, it is applied also to any velocity (because velocity is spce/time), and thus it is applied to C also.

Are you saying that the photon is now travelling at 2c? If so that is incorrect.

If not, can you please restate?

 

Or:

if the road is 10 inches long, one inch travel is 10% of the road.

 

When suddenly the road extends to 20 inches long (by scaling), then one "scaled-inch" still is 10% of the length, or 2 inches. The important thing is that for the same time, the distance as measured in the new space system (the scaled-space) remains constant: that's the main property of C.

Again, it sounds as if you are saying that even though space between 2 objects has increased, that it will not take any additional time for a photon to travel between those 2 objects. If that is what you are saying, it is incorrect.

 

What is a 'scaled inch'? Does it have different physical properties than a regular inch?

 

Can you define 'scaling' (as in, 'the road extends...by scaling'? Is scaling synonymous to 'metric expansion'?

 

Twenty inches are twenty inches. If a photon takes x amount of time to traverse 10 inches, it takes twice as much time to traverse 20 inches, whether you call them 'scaled' or not.

[Iggy]

But it is because I believe them, and because we see the galaxy now, that I am sure we will always see the galaxy, when we look in that direction. It can never run out of photons, as long as it exists. And those photos, that started out in our direction, have only essentially three attributes, relative to us. 1. They are on their way to us, 2. They are now reaching us, 3. They missed us on the way by and are on their way to some area of space behind us (should we be facing the galaxy in question). There is not an age we can reach where these three conditions are not still valid.

The size of the telescope needed to make the observation is the limiting factor. That's why Krauss added the qualifier about the size of the telescope in his remarks.

 

---

 

I don't think it is that simple.

 

When the road grows by 2 inches, it means that there is scale factor of 2.

It is even less simple. The scale factor grows (even if the universe is always expanding at a constant rate) over time. If the scale factor is one today (it usually is set that way) then the scale factor will be two when the distance between things doubles (from what they are today).

 

When the scale factor is applied to space, it is applied also to any velocity (because velocity is spce/time), and thus it is applied to C also.

That's why we observe galaxies receding at apparent speed multiple of C.

 

Or:

if the road is 10 inches long, one inch travel is 10% of the road.

 

When suddenly the road extends to 20 inches long (by scaling), then one "scaled-inch" still is 10% of the length, or 2 inches. The important thing is that for the same time, the distance as measured in the new space system (the scaled-space) remains constant: that's the main property of C.

Not at all. Imagine gluing pennies to a rubber sheet. As you stretch the sheet the thing that remains constant is the speed of the photon relative to the size of a penny. If you draw a grid on a rubber sheet, and stretch it, the speed of the photon relative to the grid is not constant.

 

Your conclusion is true that photons are currently arriving here in the Milky Way which started out getting further away from us (that's why the past lightcone on the spacetime diagrams have a teardrop shape). The photons were pointed at us and trying to make their way across the distance to us, but space was expanding too quickly back then so that the distance between the Milky Way and the photon was initially increasing. The reason we see those photons is because expansion decelerated for the first few billion years sufficiently that some photons did cross the Hubble distance and started making progress in our direction.

 

The deceleration of expansion fell less and less until it became negative (which is the onset of acceleration... negative deceleration is acceleration). Any photon emitted towards us now by a galaxy with a current superluminal recession speed will never reach us. They will move away from us at an ever increasing rate.

Edited October 12, 2012 by Iggy

[michel123456]

(...)Not at all. Imagine gluing pennies to a rubber sheet. As you stretch the sheet the thing that remains constant is the speed of the photon relative to the size of a penny. If you draw a grid on a rubber sheet, and stretch it, the speed of the photon relative to the grid is not constant.

(...)

 

??? that is forbidden by Relativity. The speed of a photon must remain constant. and for that to be true the speed must be relative to the size of the grid.

 

Are you saying that the photon is now travelling at 2c? If so that is incorrect.

If not, can you please restate?

 

 

Again, it sounds as if you are saying that even though space between 2 objects has increased, that it will not take any additional time for a photon to travel between those 2 objects. If that is what you are saying, it is incorrect.

No, I'll try to restate. C is constant. See below.

 

 

What is a 'scaled inch'? Does it have different physical properties than a regular inch?

a "scaled inch" is an inch in a scaled metric system (imperial system) or if you prefer it is an "expanded inch" in an "expanded metric".

 

Can you define 'scaling' (as in, 'the road extends...by scaling'? Is scaling synonymous to 'metric expansion'?

 

Twenty inches are twenty inches. If a photon takes x amount of time to traverse 10 inches, it takes twice as much time to traverse 20 inches, whether you call them 'scaled' or not.

Yes, scaling=metric expansion but scaling has a wider meaning : it can be both expansion or contraction.

 

when c=m/s in one system,

 

then C=M/S in the second system

 

If space only is scaled by two then we have M=2m and s=S (because time is not scaled)

Edited October 12, 2012 by michel123456

[tar]

377,000 years, not three seconds.

 

 

 

You couldn't see any distance at all. A uniform fog of ions means that photons could barely travel any distance before absorbtion.

 

 

 

There was no 'clearing'. It happened everywhere at just about the same time, as the temperature of the universe dropped below a 3000K.

 

ACG52,

 

Excuse me for using my own frame of reference and not being specific about it. The three seconds I am using, is a "human" moment. It is our timescale and here and now sense, that I am giving to the eternal observers, stationed at the position of the Milky Way, before it formed. When the universe went transparent, it happened everywhere in the time frame you are suggesting, but I am an observer of the event, without godlike powers to see it all at once. A photon can not reach me, that was emitted during a time prior the clearing. One second after the clearing,(from a godlike perspective), I as a Milky Way area observer, could not possibly "see" further than 196,000 miles. After three seconds (a human moment) I could see no further than 600,000 miles.

 

That was the picture I was painting. Not the clearing happening from a Godlike perspective, but the clearing happening from an observer's perspective. And that is the best way to look at it, because that is the way we see it.

 

Regards, TAR2

[Iggy]

??? that is forbidden by Relativity. The speed of a photon must remain constant. and for that to be true the speed must be relative to the size of the grid.

 

 

No, I'll try to restate. C is constant. See below.

c is constant in special relativity and not constant in general relativity (general relativity is the more general case of relativity... the complete theory). Expanding cosmic models are solutions of general relativity because one thing that makes special relativity special is that it can't handle expanding metrics like your analogy.

 

By the way... galaxies don't expand compared to expanding space. If the speed of light were constant compared to an expanding metric like you say then it would be variable compared to observers that don't expand in galaxies that don't expand like pennies glued on the rubber sheet.

[michel123456]

c is constant in special relativity and not constant in general relativity (general relativity is the more general case of relativity... the complete theory). Expanding cosmic models are solutions of general relativity because one thing that makes special relativity special is that it can't handle expanding metrics like your analogy.

 

By the way... galaxies don't expand compared to expanding space. If the speed of light were constant compared to an expanding metric like you say then it would be variable compared to observers that don't expand in galaxies that don't expand like pennies glued on the rubber sheet.

(bolded mine)

Isn't it exactly what we are observing?

C is constant for us (all photons reach us at C) but we observe galaxies receding at speeds multiple of c.