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tommac
2009-Jan-05, 02:12 PM
If I was travelling at near the speed of light in a space ship, then I turned off my engines and just let me slow down ( first of all would I ??? if not lets say I have other engines that slow me down ) When I was travelling fast, my time relative to everything else was running differently, as I slow down ... do I see everyone elses space-time expand?

tusenfem
2009-Jan-05, 02:30 PM
I think somewhere on the web there is a application that shows you what happens with your surroundings when you accelerated to near light speed. You would see everything change yes.

ETA: Ah, here is the link (http://www.spacetimetravel.org/tuebingen/tuebingen5.html) that I was looking for.

Ken G
2009-Jan-05, 02:43 PM
You would only slow down if you were experiencing friction of some kind, like air resistance or drag. Remember that to you, you would still not be moving at all, but you'd note a prevailing tendency for space stuff to be zooming toward you all from one direction (and you might attribute that break in isotropic symmetry to motion on your own part, or you might remember your spaceship blasting off, so you'd have plenty of reason to attribute the motion as being your own-- though the laws of physics themselves would not require that you imagine you were moving). So from that perspective, the concept of "drag" is the tendency for all that space stuff zooming by to confer its speed to you (or penetrate right through you, in the case of dust and pebbles).

So let's say instead you use a rocket to accelerate in the same direction as all the space stuff zooming past you (that's what you might attribute to "slowing yourself down"). Then you enter an accelerating reference frame, and if you choose to apply Einstein's special-relativity-inspired conventions for conceptualizing a global coordinate system around yourself as you accelerate, you would be using what is known as a "Rindler metric" to construct that global coordinate system. That construction would have several rather bizarre attributes-- it would seem like the space stuff was slowing down and therefore undergoing less length contraction, it's time would appear to be speeding up as the time dilation reduced, and, in addition, there would be a continuous shifting in your concept of simultaneity, such that time would appear to be going backward in a large part of the universe way out in front of you from where all that space stuff is zooming from. It might seem to you that the Einstein convention, and its associated global reference frame, was not terribly useful in your accelerating reference frame, because it was inspired by considering inertial observers.

tommac
2009-Jan-05, 05:54 PM
cool ... great post.

Where I was going with this was ... if at a big bang or white hole or whatever we were travelling at the speed of light we would be able to travel very far in reference to space-time relativeness. As we slowed down ... would it appear that everything is moving away from each other because of relativistic effects ?

Sorry about the wording ... trying to quickly form some thoughts here ...

You would only slow down if you were experiencing friction of some kind, like air resistance or drag. Remember that to you, you would still not be moving at all, but you'd note a prevailing tendency for space stuff to be zooming toward you all from one direction (and you might attribute that break in isotropic symmetry to motion on your own part, or you might remember your spaceship blasting off, so you'd have plenty of reason to attribute the motion as being your own-- though the laws of physics themselves would not require that you imagine you were moving). So from that perspective, the concept of "drag" is the tendency for all that space stuff zooming by to confer its speed to you (or penetrate right through you, in the case of dust and pebbles).

So let's say instead you use a rocket to accelerate in the same direction as all the space stuff zooming past you (that's what you might attribute to "slowing yourself down"). Then you enter an accelerating reference frame, and if you choose to apply Einstein's special-relativity-inspired conventions for conceptualizing a global coordinate system around yourself as you accelerate, you would be using what is known as a "Rindler metric" to construct that global coordinate system. That construction would have several rather bizarre attributes-- it would seem like the space stuff was slowing down and therefore undergoing less length contraction, it's time would appear to be speeding up as the time dilation reduced, and, in addition, there would be a continuous shifting in your concept of simultaneity, such that time would appear to be going backward in a large part of the universe way out in front of you from where all that space stuff is zooming from. It might seem to you that the Einstein convention, and its associated global reference frame, was not terribly useful in your accelerating reference frame, because it was inspired by considering inertial observers.

gzhpcu
2009-Jan-05, 06:02 PM
cool ... great post.

Where I was going with this was ... if at a big bang or white hole or whatever we were travelling at the speed of light we would be able to travel very far in reference to space-time relativeness. As we slowed down ... would it appear that everything is moving away from each other because of relativistic effects ?

Sorry about the wording ... trying to quickly form some thoughts here ...

First of all, you can not travel at the speed of light, it would take an infinite amount of energy to do so.

If you could, everything around you would appear to be frozen, and the distance between objects would be zero. If you were to slow down, it would appear to you that the distance between objects would increase.

tommac
2009-Jan-05, 06:06 PM
First of all, you can not travel at the speed of light, it would take an infinite amount of energy to do so.

If you could, everything around you would appear to be frozen, and the distance between objects would be zero. If you were to slow down, it would appear to you that the distance between objects would increase.

Kind of like the inflation period right? Isnt that before space-time existed?

gzhpcu
2009-Jan-05, 06:54 PM
Kind of like the inflation period right? Isnt that before space-time existed?

As I understand it, space-time existed during the inflationary period. It did not exist at time = 0. During this brief period our physics was not valid.

tommac
2009-Jan-05, 07:10 PM
As I understand it, space-time existed during the inflationary period. It did not exist at time = 0. During this brief period our physics was not valid.

I thought inflation was superluminal ...

gzhpcu
2009-Jan-05, 07:19 PM
I thought inflation was superluminal ...
Yes, but our physics breaks down here (and GR as well)

tommac
2009-Jan-05, 07:28 PM
Yes, but our physics breaks down here (and GR as well)

OK great ... so lets go back to #4 above:

gzhpcu
2009-Jan-05, 07:44 PM
OK great ... so lets go back to #4 above:

Aren't we going into a loop? Or am I missing something? :confused:

tommac
2009-Jan-05, 10:22 PM
Aren't we going into a loop? Or am I missing something? :confused:

we took a detour due to your post:

First of all, you can not travel at the speed of light, it would take an infinite amount of energy to do so.

Now that we showed that you could have ... we can move on

grant hutchison
2009-Jan-05, 11:34 PM
we took a detour due to your post:
First of all, you can not travel at the speed of light, it would take an infinite amount of energy to do so.Now that we showed that you could have ... we can move onWhere did "we" show that?

Grant Hutchison

cosmocrazy
2009-Jan-05, 11:46 PM
we took a detour due to your post:

Now that we showed that you could have ... we can move on

I enjoy reading most of the questions and answers replied that are posted on your threads Tom, but i'm lost with this one. Could you clarify some.:confused:

Thanks.

astromark
2009-Jan-06, 01:04 AM
Rules of this universe; Any particle of mass can not attain the velocity C. end of question.

gzhpcu
2009-Jan-06, 03:11 AM
Now that we showed that you could have ... we can move on

Once more, we can not discuss what happened during the inflationary period because our physics no longer applies. Traveling at c. with all the implications of GR, during this period is, in this context, meaningless since GR does not apply. So what do you mean by your statement?:confused:

grant hutchison
2009-Jan-06, 10:35 AM
Once more, we can not discuss what happened during the inflationary period because our physics no longer applies. Traveling at c. with all the implications of GR, during this period is, in this context, meaningless since GR does not apply. So what do you mean by your statement?:confused:I'd point out that superluminal expansion of the Universe is taking place right now. It's not something that is restricted to the inflationary era, and it's not incompatible with GR.

I think tommac is frustrated because your comment about lightspeed has moved the thread away from his OP.
Tommac, you're going to get such comments every single time you set up a thought experiment with an impossible observer who blows up the relativity equations: either by moving at lightspeed or by hovering on the event horizon of a black hole. It doesn't take long to type the word "nearly", and it might save you a lot of hassle. :)

Grant Hutchison

gzhpcu
2009-Jan-06, 10:55 AM
I'd point out that superluminal expansion of the Universe is taking place right now. It's not something that is restricted to the inflationary era, and it's not incompatible with GR.

Yes, but I meant it in the context of Tommac's questions.

Superluminal expansion of the universe is not in contradiction with special relativity when it occurs outside the observer’s inertial frame.

gzhpcu
2009-Jan-06, 11:04 AM
It would be more appropriate to describe the inflationary period as superluminal expansion if all distances down to the Planck length were receding faster than the speed of light.

source:http://arxiv.org/PS_cache/astro-ph/pdf/0310/0310808v2.pdf

WayneFrancis
2009-Jan-06, 02:22 PM
If I was travelling at near the speed of light in a space ship, then I turned off my engines and just let me slow down ( first of all would I ??? if not lets say I have other engines that slow me down ) When I was travelling fast, my time relative to everything else was running differently, as I slow down ... do I see everyone elses space-time expand?

The rate of time dilation is not dependant on how long you are traveling but how much you accelerated/deccelerated relative to another object.

ie accelerating to .9c puts you at about 7 x time dialation.

So yes when you speed up to .9c relative to an object you are approaching then that distance will seem to shrink by 7x. But when you slow back down the distance in the direction of travel with expand by 7x

The space dilation is not in all directions either. Looking out perpendicular the distances will seem to remain the same.

WayneFrancis
2009-Jan-06, 02:25 PM
we took a detour due to your post:

Now that we showed that you could have ... we can move on

where have you shown that anything with a non zero rest mass can get to the speed of light?

WayneFrancis
2009-Jan-06, 02:27 PM
Oh I see...Tommac thinks that inflation = movement which is wrong. During inflation no objects where really moving > C. They where moving at relative speed and space was introduced. It is a bit different but a critical difference.

tommac
2009-Jan-06, 04:03 PM
Where did "we" show that?

Grant Hutchison I think when we showed that the laws of relativity were not in effect yet. If relativity does not limit stuff then what law prevents super luminal travel?

tommac
2009-Jan-06, 04:05 PM
Rules of this universe; Any particle of mass can not attain the velocity C. end of question.

Based on what? Is that true for all universes?

How about before time or right when time came into existance?

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"

tommac
2009-Jan-06, 04:07 PM
Once more, we can not discuss what happened during the inflationary period because our physics no longer applies. Traveling at c. with all the implications of GR, during this period is, in this context, meaningless since GR does not apply. So what do you mean by your statement?:confused:

It is really an unimportant part of the question. The question was meant that whatever happened during inflation we ( everything ) were travelling quickly and time existed ... as we slow down ... would the universe appear to be moving away faster because of time dialation.

gzhpcu
2009-Jan-06, 04:08 PM
I think when we showed that the laws of relativity were not in effect yet. If relativity does not limit stuff then what law prevents super luminal travel?

Our physics breaks down during the inflationary period. We have no idea what laws prevail, and therefore can not make any statement either way.

gzhpcu
2009-Jan-06, 04:10 PM
It is really an unimportant part of the question. The question was meant that whatever happened during inflation we ( everything ) were travelling quickly and time existed ... as we slow down ... would the universe appear to be moving away faster because of time dialation.

Until we find laws of physics which apply to this period, we can't say.

grant hutchison
2009-Jan-06, 04:26 PM
I think when we showed that the laws of relativity were not in effect yet. If relativity does not limit stuff then what law prevents super luminal travel?Well, we know General Relativity is definitely inadequate to describe the Planck Era, before 10-43s. But the Inflation Era comes after that time. So GR may or may not be strictly applicable during inflation. But it doesn't really matter, since GR does not forbid superluminal expansion, either during the Inflation Era or now.
Which is fortunate, since the Universe is undergoing superluminal expansion right at this moment, according to the standard model.

Grant Hutchison

Ken G
2009-Jan-06, 04:38 PM
If it is unclear to any what is meant by "superluminal expansion", it means that the number of some standard-sized object that would be needed to be laid end-to-end between two regions of the universe separated by a sufficiently huge distance d is increasing with the age of the universe, at a rate that exceeds c/d. Equivalently, it means that the time measured on standard clocks for light to be exchanged between these distant regions is increasing with age, also at a rate that exceeds c/d.

Whether or not that should really be called "superluminal" is another issue-- note that even in special relativity it is perfectly possible for this to be true (it holds, for example, if we look at two objects each moving at 0.9c away from each other in our reference frame, and we are laying the reference objects end-to-end between them, as we will find the number of reference objects we need to do this will increase at the rate 1.8 c/d, yet few would call that situation "superluminal").

If anyone has a hard time seeing why the universe could expand that fast without violating relativity, note that the exact same condition could be achieved if the universe was not doing anything except having the reference objects (and every other object obeying the same physical constraints) shrinking with age, and the standard clocks speeding up with age. The physics of that situation can be made identical in every way to the expansion picture, but it's a lot clearer how the universe can be "superluminal" when nothing is moving at all, since the shrinking of objects and speeding of clocks can occur at any rate you like without violating relativity.

If anyone doesn't like imagining shrinking objects and speeding clocks, that's fine too, just imagine that space expands, and recognize that it can expand at any rate without violating relativity, because relativity limits the speed that two objects can pass by each other at the same point, not how fast widely separated objects can continue to separate. Global coordinatizations are arbitrary and lead to all kinds of misconceptions if one expects them to have physical meaning.

tommac
2009-Jan-06, 04:54 PM
If anyone doesn't like imagining shrinking objects and speeding clocks, that's fine too, just imagine that space expands, and recognize that it can expand at any rate without violating relativity, because relativity limits the speed that two objects can pass by each other at the same point, not how fast widely separated objects can continue to separate. Global coordinatizations are arbitrary and lead to all kinds of misconceptions if one expects them to have physical meaning.

Doesnt it also mean that from an objects perception that another object can not detect another object moving away from it as faster than the speed of light? Why would they need to pass each other? 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?

tommac
2009-Jan-06, 04:55 PM
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? )

Ken G
2009-Jan-06, 05:22 PM
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.

gzhpcu
2009-Jan-06, 05:23 PM
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?

Ken G
2009-Jan-06, 05:29 PM
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).

tommac
2009-Jan-06, 06:16 PM
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.

Ken G
2009-Jan-06, 06:25 PM
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.

tommac
2009-Jan-06, 07:51 PM
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

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.

Ken G
2009-Jan-07, 01:01 AM
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".

grav
2009-Jan-07, 02:01 AM
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.

WayneFrancis
2009-Jan-07, 02:48 AM
Based on what?

Based on everything we know so far.

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?

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?

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.

WayneFrancis
2009-Jan-07, 02:57 AM
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.

tommac
2009-Jan-07, 02:51 PM
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 ... :confused:

WayneFrancis
2009-Jan-08, 02:25 AM
Why blueshifted? If we are percieving things to move away from us then we would also percieve the redshift. Please explain ... :confused:

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

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 us
We have to explain why things further away are travelling faster then things closer
We 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.

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 happening
If 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

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.

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.

grav
2009-Jan-08, 02:35 AM
Why blueshifted? If we are percieving things to move away from us then we would also percieve the redshift. Please explain ... :confused: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!

tommac
2009-Jan-08, 03:14 PM
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 ...

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 happening
If 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

tommac
2009-Jan-08, 03:24 PM
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. :lol:

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!

gzhpcu
2009-Jan-08, 03:28 PM
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.

tommac
2009-Jan-08, 03:35 PM
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.

gzhpcu
2009-Jan-08, 03:43 PM
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)

tommac
2009-Jan-08, 04:00 PM
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 ( :shifty: threw this in to get more responses ) .

gzhpcu
2009-Jan-08, 04:57 PM
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.

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?

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 ( :shifty: 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.

tommac
2009-Jan-08, 05:05 PM
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.

gzhpcu
2009-Jan-08, 05:30 PM
I am saying if ALL space-time expands ... not just between objects.
I understood that.

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.

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?:confused:

tommac
2009-Jan-08, 08:41 PM
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?:confused:

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?

speedfreek
2009-Jan-08, 08:45 PM
Why do you think you would have the same redshift in that scenario?

tommac
2009-Jan-08, 08:56 PM
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.

speedfreek
2009-Jan-08, 10:49 PM
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?

grav
2009-Jan-08, 10:50 PM
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.

grav
2009-Jan-14, 11:13 PM
I'm still attempting to work through some of the details on my own, but here (http://www.bautforum.com/questions-answers/83337-accelerating-observer-contraction.html#post1407329)'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.

tommac
2009-Jan-16, 05:59 PM
I'm still attempting to work through some of the details on my own, but here (http://www.bautforum.com/questions-answers/83337-accelerating-observer-contraction.html#post1407329)'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?

spratleyj
2009-Jan-16, 10:58 PM
First of all, you can not travel at the speed of light, it would take an infinite amount of energy to do so.

That's assuming that he has mass. Of course he could be massless;)

grav
2009-Jan-17, 03:27 AM
which is what we would be experiencing as the thing slowing down right?Right. It doesn't matter what the apparent relative speed due to Lorentz contraction at a distance is, or if the observer is accelerating or decelerating. The Relativistic Doppler is the same coming from an emitter at any distance in the stationary frame, depending only upon the instantaneous local relative speed to that part of the stationary frame that coincides with the observer as he passes it.

gzhpcu
2009-Jan-17, 03:43 AM
That's assuming that he has mass. Of course he could be massless;)

Not really, because tommac was speaking of slowing down from the speed of light. Neutinos, photons and gravitons must always go at the speed of light. They can not slow down...:)

spratleyj
2009-Jan-17, 04:34 AM
Not really, because tommac was speaking of slowing down from the speed of light. Neutinos, photons and gravitons must always go at the speed of light. They can not slow down...:)

Of course that's assuming that (he) can't change from a massless state to one in which (he) has mass :)

DoctorScience
2009-Jan-17, 06:56 AM
Ok well, First off if "imaginary mass" or "tachyons" do wind up exsisting then faster then light travel is possible and you can go anywhere in the universe instantly.
Now if you can put up an electromegnetic field and use a power sorce to make you "imaginary mass" you would only travel faster then light as long as you had the field up thats serperating you from the physical mass around you. so, your going inbetween the fabric of time and space to acheive these speeds. So we'd have to become a type 3 civilization. but in conventunal science today you could possibly go up to 2 thirds the speed of light. The faster you go the higher the time dilation so. Its possible to go close the the speed of light and make a "20" year journey and you'd experience a fraction of that. as your going fast enough to effect time. so possibly you could make a 80 year journey and walk out of the spaceship with it only being a meer couple of years in your prospective. but, you would need to get nearly the speed of light. I call this effect "Einstein's clock." where he's traveling closer and closer to the speed of light and he notices his clock is ticking slower and slower and slower. Well anyways to go indepth with physics would take a very long time. there are many aspects to this question and no simple answers.

Sincerely, (K)

DoctorScience
2009-Jan-17, 06:59 AM
btw the clock is out side of the spaceship.. not inside.. in Einsteins clock effect. in the space ship time would "seem" to be going the same rate.

gzhpcu
2009-Jan-17, 07:56 AM
Ok well, First off if "imaginary mass" or "tachyons" do wind up exsisting then faster then light travel is possible and you can go anywhere in the universe instantly.
Sincerely, (K)
FTL is allowed by special relativity, but the c barrier still exists. If tachyons exist, and this is a big "if", they can go faster than the speed of light, but can not slow down to reach the speed of light. So it can not slow down to subluminal speeds. The barrier works in both directions.

t'=t x sqrt(1-v2/c2)

For a tachyon with v = 2c,

t'=t x i x sqrt (3)

resulting in an imaginary number.

This leads to time paradoxes (tachyon has negative time and goes backward in time, etc.)

speedfreek
2009-Jan-17, 08:21 PM
btw the clock is out side of the spaceship.. not inside.. in Einsteins clock effect. in the space ship time would "seem" to be going the same rate.

It doesn't matter if the clock is outside or inside the spaceship, as long as the clock is moving with the spaceship the clock will show time-dilation when compared to a clock that isn't moving with the space ship.

And in the space ship, time doesn't just "seem" to passing at the normal rate of one second per second, time is passing at the normal rate. There is no experiment that anyone on that space ship could do to show otherwise. If a second is defined by the speed at which caesium atoms "vibrate", any caesium atoms on the spaceship would be vibrating at exactly the right speed when measured by the ships clock.

Locally to any clock, time always passes at one second per second. But if you take two initially synchronised clocks and put one of them on an space ship and fly it to the moon and back, when you bring the clocks back together they will show different elapsed times. The clocks didn't actually tick at different speeds, but when compared with each other they took different paths through space-time and one of those paths took less seconds than the other. The faster you move through space, the slower you move through time, but time always passes at the same rate for you whatever you are doing. It is what you are doing when compared to what someone else is doing that makes the difference.