1. All of this is way off topic from the OP ... basically what I was saying is that as I slow down from going the speed of light ... because of relativity would i percieve everything moving away from everything else. could this effect happen from reverse space-time dilation ? ( during slowdown? )

2. Originally Posted by tommac
All of this is way off topic from the OP ... basically what I was saying is that as I slow down from going the speed of light ... because of relativity would i percieve everything moving away from everything else. could this effect happen from reverse space-time dilation ? ( during slowdown? )
The answer is yes, but only if you choose a particular (special-relativity inspired and centered on you) way to determine what is the distance between things. The key point here is, you can think of a distance as being the manifestation of a coordinatization, or you can think of it as being the outcome of a measurement. The difference is that the first is purely mathematical, whereas the second requires that you specify an observer capable of doing the measurement (at least in principle, as they can be hypothetical). Since you are specifying an observer in the latter case, you are free to place that observer in any reference frame you like, and that's where the arbitrariness appears that is already present in the mathematical coordinate choice. The bottom line is, there is really no such thing, in any absolute way, as "the distance between two objects", but there is the distance as perceived by some observer using some definition of distance. If you specify that you are the observer, and you take some special-relativity-inspired way to determine distances, then yes, you will find that as you "slow down" the distances between objects, along the direction of your slowing down, will increase. Will that look like cosmic inflation? No, cosmic inflation is isotropic and is measured by local observers spread out over the universe, and then translated using GR into your reference frame, which is different from being the outcome of measurements done by you and interpreted as reverse-length-contraction.

3. Originally Posted by tommac
All of this is way off topic from the OP ... basically what I was saying is that as I slow down from going the speed of light ... because of relativity would i percieve everything moving away from everything else. could this effect happen from reverse space-time dilation ? ( during slowdown? )
I hate to say this, but you can't go the speed of light. Let's say rather close to the speed of light. You would perceive everything moving away from everything else, but only in the direction parallel to that which you are traveling.

What do you mean by reverse space-time dilation?

4. Originally Posted by tommac
If we have point A and B
and a detector on point A can A ever detect that point B is moving away from it faster than the speed of light?
Yes it can, but it depends on what you mean by "moving away from it". If by that, you just mean "the distance is interpreted as increasing at a rate faster than c", then yes, we have quasars that we observe that we interpret as having distances that increase faster than c. However, we do not picture that as being due to "motion away" from us, we picture that as being due to the expansion of space itself. The problem is, motion is a locally defined concept-- it applies to object passing each other at the same point. It can in many situations be extrapolated to objects that are separated, but these other meanings of motion are coordinate dependent, and lead to all kinds of misconceptions when applied on the large scales of the universe (though they work fine on smaller scales like in our solar system).

5. Originally Posted by Ken G
The answer is yes, but only if you choose a particular (special-relativity inspired and centered on you) way to determine what is the distance between things.
I am OK with that as we are currently the ONLY observer. If we are the only observer than our existance is important and our relative view can be self-centered as in the case of observation ARE the only observers.

6. Originally Posted by tommac
I am OK with that as we are currently the ONLY observer. If we are the only observer than our existance is important and our relative view can be self-centered as in the case of observation ARE the only observers.
But interestingly, the structure of the laws of physics themselves afford a huge importance to other observers, even if they are hypothetical. If you take the perspective that we are the only observers "who count", in some sense, then you have the nagging problem to explain why the laws of physics come out the same for all those other hypothetical observers, who don't count, as they come out for us, who do. Why equip the universe with all that redundancy in laws that only matter for our own perspective?

Furthermore, I do not mean to imply that once we specify the observers, we get the global coordinatization that tell us the distances you are talking about. If we don't employ local observers, then we also have to choose the conventions we will apply to generate that global coordinatization from our own vantage point. We can apply the conventions of special relativity, and get what you are talking about, but that's still an arbitrary choice (it elevates the importance of inertial observers). So there are two levels of arbitrariness: arbitrariness in the observing reference frame, and arbitrariness in the conventions. Your statement above can be used only to relieve that first level of arbitrariness. If we will still be left with arbitrariness, it seems unnecessary to accept the awkwardness of treating ourselves as special when the laws themselves do not.

7. Maybe I mistated my point.

Lets say ALL observers dont observe that all galaxies are moving further away. Lets say that only some observers ( lets arbitrarily say that 49% see them all expanding )

Now ... lets say we are the ones that see them expanding ... and we are ones that see them expanding faster and faster.

Does this effect what others observe? Does this mean that we are the center of the universe ... no ... if just means that we are observing the way we are observing.

I dont know if the other galaxies are seeing things in the same way as we are. I am not sure if a photon looking at the universe sees galaxies expanding or contracting ... I dont know if at the EH of a black hole if the galaxies are expanding ... etc ... We have never observed from there so we just dont have that data. We can state that our observations are not unique without jumping to the conclusion that we are in the center of the universe.

We can only say that from our observations ... we may observe things that are unique to our vantage point ... only to be shared with other observers who share the exact variables that can come into the observation .

Ugggg .... I need writing lessons ... does any of that make sense

Originally Posted by Ken G
But interestingly, the structure of the laws of physics themselves afford a huge importance to other observers, even if they are hypothetical. If you take the perspective that we are the only observers "who count", in some sense, then you have the nagging problem to explain why the laws of physics come out the same for all those other hypothetical observers, who don't count, as they come out for us, who do. Why equip the universe with all that redundancy in laws that only matter for our own perspective?

Furthermore, I do not mean to imply that once we specify the observers, we get the global coordinatization that tell us the distances you are talking about. If we don't employ local observers, then we also have to choose the conventions we will apply to generate that global coordinatization from our own vantage point. We can apply the conventions of special relativity, and get what you are talking about, but that's still an arbitrary choice (it elevates the importance of inertial observers). So there are two levels of arbitrariness: arbitrariness in the observing reference frame, and arbitrariness in the conventions. Your statement above can be used only to relieve that first level of arbitrariness. If we will still be left with arbitrariness, it seems unnecessary to accept the awkwardness of treating ourselves as special when the laws themselves do not.

8. Originally Posted by tommac
Does this effect what others observe? Does this mean that we are the center of the universe ... no ... if just means that we are observing the way we are observing.
It sounds like the concept you are looking for is what is called an "invariant", which are things that all observers can agree on no matter what their reference frame or their inspiration for generating global coordinates. The concept of invariants is quite important in relativity, and one might say that only invariants are "real".

9. Interesting idea, but the main reason we think the universe is expanding in the first place is because we measure an overall redshift of the light from stars in every direction minus peculiar speeds. If we were moving at some large speed relative to a static universe and then decelerated back toward rest in the stationary frame, then the distances between stars and galaxies in the stationary frame would appear to become greater, at least along the line of travel, while also taking into account relativistic beaming (aberration) in other directions and all that, but the light from stars that lie in front of us would be blueshifted initially while inertial and remain blueshifted during deceleration, just to a lesser and lesser degree until we came to rest, and all by the same amount regardless of the distance directly in front of us, so that mechanism would not explain the Hubble redshift proportional to distance that is observed.

10. Originally Posted by tommac
Based on what?
Based on everything we know so far.

Originally Posted by tommac
Is that true for all universes?
I don't know...do you have any evidence for other universes and what the physical laws of those universes are?

Originally Posted by tommac
How about before time or right when time came into existance?
Do you not see the problem with the question? Before indicates time. How can something be "before" time. Its like asking what is 2 feet from no where?

Originally Posted by tommac
It really is an unimportant piece of the question ... kind of took a bad tangent here ... the OP could have easily been stated as "very close to the speed of light"
I don't know if I would call it unimportant. If you don't understand the fundamentals it is hard to ask appropriate questions about more complex issues.

11. Originally Posted by Ken G
The answer is yes, but only if you choose a particular (special-relativity inspired and centered on you) way to determine what is the distance between things. The key point here is, you can think of a distance as being the manifestation of a coordinatization, or you can think of it as being the outcome of a measurement. The difference is that the first is purely mathematical, whereas the second requires that you specify an observer capable of doing the measurement (at least in principle, as they can be hypothetical). Since you are specifying an observer in the latter case, you are free to place that observer in any reference frame you like, and that's where the arbitrariness appears that is already present in the mathematical coordinate choice. The bottom line is, there is really no such thing, in any absolute way, as "the distance between two objects", but there is the distance as perceived by some observer using some definition of distance. If you specify that you are the observer, and you take some special-relativity-inspired way to determine distances, then yes, you will find that as you "slow down" the distances between objects, along the direction of your slowing down, will increase. Will that look like cosmic inflation? No, cosmic inflation is isotropic and is measured by local observers spread out over the universe, and then translated using GR into your reference frame, which is different from being the outcome of measurements done by you and interpreted as reverse-length-contraction.
Well put I was trying to think on how to express it adequately and was falling far short. Your explanation is great.

12. Originally Posted by grav
Interesting idea, but the main reason we think the universe is expanding in the first place is because we measure an overall redshift of the light from stars in every direction minus peculiar speeds. If we were moving at some large speed relative to a static universe and then decelerated back toward rest in the stationary frame, then the distances between stars and galaxies in the stationary frame would appear to become greater, at least along the line of travel, while also taking into account relativistic beaming (aberration) in other directions and all that, but the light from stars that lie in front of us would be blueshifted initially while inertial and remain blueshifted during deceleration, just to a lesser and lesser degree until we came to rest, and all by the same amount regardless of the distance directly in front of us, so that mechanism would not explain the Hubble redshift proportional to distance that is observed.
Why blueshifted? If we are percieving things to move away from us then we would also percieve the redshift. Please explain ...

13. Originally Posted by tommac
Why blueshifted? If we are percieving things to move away from us then we would also percieve the redshift. Please explain ...
Let me see if I can put this in another way.

When we look out it appears everything is moving away from us.
There is absolutely no reason to think we are in a special place in the universe.
The further something is out from us the faster it travels.

So there are a few things that can be happening

Code:
```1) We are in a special place and everything is really moving away from us
Problems with this:
well it means we are in a special position without any real explanation as to why.if we are stationary we have to figure out what makes our position in the universe replusive to everything else, but usWe have to explain why things further away are travelling faster then things closerWe have to throw out SR because then the speeds really are relative and some objects would be travelling faster then the speed of light not only to us but to many other reference points in the universe.```
Code:
```1) All galaxies are really not moving but actually shrinking making the space look like it is getting larger between us
Problems with this:
We don't have any idea how or why this would happen.We don't have any evidence of this happeningIf it is happening we have to explain why this effect is also effecting the wave energy levels of light altering them exactly the amount needed to compensate for all the matter shrinking.   IE the idea that it should explain, red shift, falls down when you look at the data.  For example with shrinking matter you would expect all red shifts to be the same and it would be directly related to the amount we shrank not the distance an object is from us.  We would also be able to measure this change in energy levels of photons at a local scale which we don't```
Code:
```1) All galaxies are really not moving but the photons are just getting "tired" and loosing energy
Problems with this:
There is no known mechanism for a photon to get "tired"Tired photons would say that photons don't have a zero rest mass and actually experience time meaning SR is wrong.```
Code:
```1) All galaxies are really not moving but the space in between is actually increasing
Problems with this:
There is no known cause for this inflation of space (we call it dark energy)```
Notice the last one's only problem is that we don't know the cause. Not that it breaks well known and tried and tested theories. Sure GR might be wrong like Newtonian mechanics was technically wrong.

Also note the main stream ideas are supported by multiple lines of evidence.

Sure some magical might happen if we looked at the universe from some other position but we have no evidence of this and thus no reason to think it is true. All the evidence points to the physical laws being the same everywhere in the universe. Helium here in our galaxy acts exactly like helium in a galaxy that is 13 billion light years away.

The static universe had SOOO many problems before red shifts, the CMBR and other recent discoveries came along. Trying to explain the red shift in a static universe is just ignoring all the other fatal flaws in that ideas.

Currently I'm having this discussion with a friend, self proclaimed conspiracy lover, who has a big problem with the big bang. Every time I point out the basic fatal flaws of a static infinitely old universe he wants to ignore them and try to explain why expansion is wrong and the static universe would be a better fit to some data point like red shift without grasping that when he invents some mysterious force that is causing all matter to shrink while properly adjusting all photons energy levels that this mysterious force is in just as bad of a position as Dark Energy being unknown. But with Dark energy there is actually more then 1 line of evidence that supports it.

14. Originally Posted by tommac
Why blueshifted? If we are percieving things to move away from us then we would also percieve the redshift. Please explain ...
If we were to consider the universe to be static in a stationary frame, and we are moving at some large relative speed to that frame, then the light we receive from the stars in front of us would be blueshifted. If we were to then decelerate in the opposite direction of our line of travel, then the distances between stars and galaxies would appear to become greater, the distances expanding equally to the front and back of us at least, but we would still be travelling toward the stars in front of us at the same time that they are "expanding" away. The stars closest to us will always remain blueshifted to some degree as we decelerate until we pass the point of rest in the stationary frame and begin moving in the opposite direction, whereas the closest stars in the opposite direction will then become blueshifted instead.

Upon further reflection, though, and what you replied, I'm now saying only the stars closest to us will remain blueshifted whereas in my last post I said the stars directly along the line of travel in front of us would all be blueshifted by the same amount regardless of the distance. I was thinking before that only the instantaneous relative speed to the stars, or to the stationary frame in general, would be all that mattered as far as the redshift or blueshift goes, but now I realize that if all distances expand to the same degree upon deceleration, then stars at twice the distance will have the appearance of moving away twice as fast with twice the redshift and so forth, just like the Hubble relationship after all, so there must be something to do with the simultaneity shift during deceleration there which determines different measured relative speeds at different times that varies with distance. Considering this, the original blueshift for stars at any distance, due to our initial inertial relative speed, will only add to that, then, while it seems the redshift should indeed increase with greater distance during deceleration, making the blueshift a local effect only, so it would seem an overall redshift in all directions at large distances would indeed predominate, which tends to agree with what you were saying after all. Oops. Sorry about that.

Thinking about it even further, though, as we decelerate, if the distance between the stars appears to be expanding, then their relative speeds away from us also becomes greater with greater distance, so even our own relative speed to the stationary frame is not an invariant except locally, since it varies with distance to individual stars even though the stars themselves are stationary to each other, so the rate of expansion between stars may not be constant either, but vary with distance as well. If stars that are very far away cannot recede faster than the speed of light relative to us, then they would be travelling away at a lesser rate than a direct Hubble expansion rate. You're right, this is confusing.

Here's one more thing. As we decelerate back into the stationary frame, if we were to stop the deceleration by simply turning off our engines (not considering gravity pulling us back while we travel inertially forward but by engines instead) when we reach the point of rest with a static universe, then everything should then be observed as stationary to each other as we are once again stationary to it as well. That appears to mean that while we were travelling forward inertially, everything else in the universe was travelling toward us at the same time and the deceleration cancels that effect. In other words, while we were travelling forward inertially, everything would appear contracted toward us along our line of travel compared to the distances observers in the stationary frame would measure, but it appears it should also mean that everything is moving toward us at a faster rate with greater distance along our line of travel in both directions, in order to be cancelled out upon decelerating back to rest when the stars are then "expanded" away from us until they reach their initial state of rest relative to us. I don't think I've ever heard anything like that with Relativity except for the Rindler horizon behind us, which might apply here, but I'm not sure how to think about it, since it would have to apply in front of us as well. It's getting complicated. Richard, help!

15. Regarding this one:

If space-time itself expanded ... then the red shift would not be constant but would be relative to the amount of space time that is in between any two objects. therefore the further away two objects were the more redshift one would see. Regardless of which observer you were you would see more redshift when looking at distant objects.

The question is as space-time expands ... do objects expand with them. I have heard that this was argued as NO ... and I am sure the same reference to the paper about the expansion of the universe will be reference with something about woody allen and brooklyn.

However ... IF space-time expanded ... and objects expanded with space time ... then wouldnt you have the same observations ...

Originally Posted by WayneFrancis
Code:
```1) All galaxies are really not moving but actually shrinking making the space look like it is getting larger between us
Problems with this:
We don't have any idea how or why this would happen.We don't have any evidence of this happeningIf it is happening we have to explain why this effect is also effecting the wave energy levels of light altering them exactly the amount needed to compensate for all the matter shrinking.   IE the idea that it should explain, red shift, falls down when you look at the data.  For example with shrinking matter you would expect all red shifts to be the same and it would be directly related to the amount we shrank not the distance an object is from us.  We would also be able to measure this change in energy levels of photons at a local scale which we don't```

16. Hahahah .... welcome to my world. This is like my drive into work in the morning. This is what I go through struggling through stuff that is way above my intellecual capabilities. That is why I usually jump over to this board and see if I can actually make any sense of what I have been thinking.

It seems that at least to some extent you are agreeing with me here ... or at minimum have fallen under the same confusion that I am.

Originally Posted by grav
If we were to consider the universe to be static in a stationary frame, and we are moving at some large relative speed to that frame, then the light we receive from the stars in front of us would be blueshifted. If we were to then decelerate in the opposite direction of our line of travel, then the distances between stars and galaxies would appear to become greater, the distances expanding equally to the front and back of us at least, but we would still be travelling toward the stars in front of us at the same time that they are "expanding" away. The stars closest to us will always remain blueshifted to some degree as we decelerate until we pass the point of rest in the stationary frame and begin moving in the opposite direction, whereas the closest stars in the opposite direction will then become blueshifted instead.

Upon further reflection, though, and what you replied, I'm now saying only the stars closest to us will remain blueshifted whereas in my last post I said the stars directly along the line of travel in front of us would all be blueshifted by the same amount regardless of the distance. I was thinking before that only the instantaneous relative speed to the stars, or to the stationary frame in general, would be all that mattered as far as the redshift or blueshift goes, but now I realize that if all distances expand to the same degree upon deceleration, then stars at twice the distance will have the appearance of moving away twice as fast with twice the redshift and so forth, just like the Hubble relationship after all, so there must be something to do with the simultaneity shift during deceleration there which determines different measured relative speeds at different times that varies with distance. Considering this, the original blueshift for stars at any distance, due to our initial inertial relative speed, will only add to that, then, while it seems the redshift should indeed increase with greater distance during deceleration, making the blueshift a local effect only, so it would seem an overall redshift in all directions at large distances would indeed predominate, which tends to agree with what you were saying after all. Oops. Sorry about that.

Thinking about it even further, though, as we decelerate, if the distance between the stars appears to be expanding, then their relative speeds away from us also becomes greater with greater distance, so even our own relative speed to the stationary frame is not an invariant except locally, since it varies with distance to individual stars even though the stars themselves are stationary to each other, so the rate of expansion between stars may not be constant either, but vary with distance as well. If stars that are very far away cannot recede faster than the speed of light relative to us, then they would be travelling away at a lesser rate than a direct Hubble expansion rate. You're right, this is confusing.

Here's one more thing. As we decelerate back into the stationary frame, if we were to stop the deceleration by simply turning off our engines (not considering gravity pulling us back while we travel inertially forward but by engines instead) when we reach the point of rest with a static universe, then everything should then be observed as stationary to each other as we are once again stationary to it as well. That appears to mean that while we were travelling forward inertially, everything else in the universe was travelling toward us at the same time and the deceleration cancels that effect. In other words, while we were travelling forward inertially, everything would appear contracted toward us along our line of travel compared to the distances observers in the stationary frame would measure, but it appears it should also mean that everything is moving toward us at a faster rate with greater distance along our line of travel in both directions, in order to be cancelled out upon decelerating back to rest when the stars are then "expanded" away from us until they reach their initial state of rest relative to us. I don't think I've ever heard anything like that with Relativity except for the Rindler horizon behind us, which might apply here, but I'm not sure how to think about it, since it would have to apply in front of us as well. It's getting complicated. Richard, help!

17. Originally Posted by tommac
Regarding this one:

However ... IF space-time expanded ... and objects expanded with space time ... then wouldnt you have the same observations ...
The Big Bang is built on the expansion of space-time. Objects do not expand with space time. You would not have the same observations, because with increasing mass you have an increasing amount of red-shift. Gravitational force is similar to acceleration away from you: it causes light to red-shift.

18. Originally Posted by gzhpcu
The Big Bang is built on the expansion of space-time. Objects do not expand with space time. You would not have the same observations, because with increasing mass you have an increasing amount of red-shift. Gravitational force is similar to acceleration away from you: it causes light to red-shift.
I never said mass increases ... that would violate some law.

I am just saying ... if space-time was expanding ... Then objects would need to expand. If you have a volume ... lets say a liter ... and the liter-second was expanding. that the water that was in that liter-second would(it could be plausable) also expand.

19. Originally Posted by tommac
I never said mass increases ... that would violate some law.

I am just saying ... if space-time was expanding ... Then objects would need to expand. If you have a volume ... lets say a liter ... and the liter-second was expanding. that the water that was in that liter-second would(it could be plausable) also expand.
Explain why objects embedded in spacetime need to expand just because spacetime expands. (BTW: This assertion is made I believe in the book "The Final Theory" by Mark McCutcheon - which has been completely criticized as pseudoscience)

20. Originally Posted by gzhpcu
Explain why objects embedded in spacetime need to expand just because spacetime expands. (BTW: This assertion is made I believe in the book "The Final Theory" by Mark McCutcheon - which has been completely criticized as pseudoscience)
I didnt say they NEED to ... just saying : "what if" ... or maybe even ... "why not"?

It space-time expands all over ..... then for example .... the space-time in between the earth and the sun would expand. Lets say it doubled ( it would be of course much less than this ... but lets say it doubled ) ... if we dont double in size then we become much more dense. the volume of the earth would be halved, the volume of the sun would be halved ... while the distance between the earth and the sun would stay the same from a space-time stand point.

So lets say that the sun expands with space-time and the earth expands with space-time then everything appears that it is staying the same proportions ... except that you will have a redshift effect from the expansion of the space-time.

I look at it ... and trust me I am probably wrong ... but the way I currently see it is similar to how space contracts near a black hole. object DO contract ... and compact ... In fact space-time is kind of flat ( 2d ( kind of ) ) at the EH ... if you extrapolate the effects of a black hole out to infinity ... couldnt you show that space contraction and time dialation can continue to expand?

I understand that for a black hole even the most massive ... the gravitational force disipates very quickly ...

However lets take say a universe sized black hole that contains gazillions of our universes of mass in it. Say where its gravitational effect pervades our universe. As we get further away from that ... our existance could resemble something emmited from a white hole ( threw this in to get more responses ) .

21. Originally Posted by tommac
It space-time expands all over ..... then for example .... the space-time in between the earth and the sun would expand. Lets say it doubled ( it would be of course much less than this ... but lets say it doubled ) ... if we dont double in size then we become much more dense. the volume of the earth would be halved, the volume of the sun would be halved ... while the distance between the earth and the sun would stay the same from a space-time stand point.

So lets say that the sun expands with space-time and the earth expands with space-time then everything appears that it is staying the same proportions ... except that you will have a redshift effect from the expansion of the space-time.
No. Objects do not become more dense if the spacetime between expands. Objects get smaller to the observer as spacetime expands.

Originally Posted by tommac
I look at it ... and trust me I am probably wrong ... but the way I currently see it is similar to how space contracts near a black hole. object DO contract ... and compact ... In fact space-time is kind of flat ( 2d ( kind of ) ) at the EH ... if you extrapolate the effects of a black hole out to infinity ... couldnt you show that space contraction and time dialation can continue to expand?

Originally Posted by tommac
However lets take say a universe sized black hole that contains gazillions of our universes of mass in it. Say where its gravitational effect pervades our universe. As we get further away from that ... our existance could resemble something emmited from a white hole ( threw this in to get more responses ) .
A black hole warps space. An object under the influence of strong gravity gets torn apart. The changes in the force of gravity are so steep that, near the black hole (and within its event horizon) the forces on your feet are much stronger than the forces on your head. The forces eventually become strong enough to tear apart everything - spaceships, astronauts, feet, cells, even atoms - via ordinary mechanical forces.

22. Originally Posted by gzhpcu
No. Objects do not become more dense if the spacetime between expands. Objects get smaller to the observer as spacetime expands.
I am saying if ALL space-time expands ... not just between objects.

we can argue the otherone later ... I am not saying this happens or not but would like to follow it through logically.

Lets say ALL space-time in the universe is expanding.

That means that all rulers are longer than they used to be, the SOL is still constant ...

If the earth did not expand with the space-time that contains the earth. then the earth would be smaller but with the same mass ... thus more dense.

Say the earth was 1 earth volume ... and space-time expanded in such a way that one earth voume-second doubled. The earth without expanding would have 1/2 the volume that it did before the expansion of space time.

but still has the same mass.

Lets for a second forget about if that is possible or not ... do we agree that is the case?

then lets go on and discuss why this isnt the case.

23. Originally Posted by tommac
I am saying if ALL space-time expands ... not just between objects.
I understood that.

Originally Posted by tommac
we can argue the otherone later ... I am not saying this happens or not but would like to follow it through logically.

Lets say ALL space-time in the universe is expanding.

That means that all rulers are longer than they used to be, the SOL is still constant ...

If the earth did not expand with the space-time that contains the earth. then the earth would be smaller but with the same mass ... thus more dense.
This is something different from the expansion of spacetime. You are saying that rulers get stretched. OK, then if the earth did not expand, it would, in this case, be denser.

Originally Posted by tommac
Say the earth was 1 earth volume ... and space-time expanded in such a way that one earth voume-second doubled. The earth without expanding would have 1/2 the volume that it did before the expansion of space time.

but still has the same mass.
OK, but what are you driving at?

24. Originally Posted by gzhpcu
I understood that.

This is something different from the expansion of spacetime. You are saying that rulers get stretched. OK, then if the earth did not expand, it would, in this case, be denser.

OK, but what are you driving at?
How would you be able to detect that vs the current understanding of universal expansion?

Basically you would have the same redshift ... are there other ways to determine that distant galaxies are moving away from us?

25. Why do you think you would have the same redshift in that scenario?

26. Originally Posted by speedfreek
Why do you think you would have the same redshift in that scenario?
you have a loss in energy ... space-time is stretching ... similar to how mainstream views it. All I am changing is that all space time is expanding ... rather than just inbetween things ...

Think of the viewpoint of something going through relativistic changes with time dialation and legnth contraction ... distances of all objects from its point of view change in distance they are away from each other.

redshift or blueshift depending if they are falling into or coming out of the well.

27. But if photons were also to expand with the universe in order to keep the speed of light constant, why would the wavelength of that light be longer when it arrived, if our rulers had expanded too?

28. Originally Posted by tommac
you have a loss in energy ... space-time is stretching ... similar to how mainstream views it. All I am changing is that all space time is expanding ... rather than just inbetween things ...

Think of the viewpoint of something going through relativistic changes with time dialation and legnth contraction ... distances of all objects from its point of view change in distance they are away from each other.
The answer to that one is simpler. If all objects expand with space-time also, then when they emit light, the wavelengths emitted from atoms would be smaller the further in the past we go, so with greater distance to the star that emitted the light. However, during transit, the wavelengths, or the distance between photons, increase with time as well, in the same proportion as the wavelengths currently emitted by the same atoms as they expand with the universe, so there would be no redshift or blueshift with distance in that case, and we wouldn't even know the universe was expanding.

29. I'm still attempting to work through some of the details on my own, but here's further reference to post #44 from another thread. It appears that an apparent greater relative speed at a distance due to contraction (or elongation) with proper acceleration does not add to the blueshift or redshift observed. It is only due to the local relative speed between frames.

30. Originally Posted by grav
I'm still attempting to work through some of the details on my own, but here's further reference to post #44 from another thread. It appears that an apparent greater relative speed at a distance due to contraction (or elongation) with proper acceleration does not add to the blueshift or redshift observed. It is only due to the local relative speed between frames.
which is what we would be experiencing as the thing slowing down right?