Solution to the Galaxy Rotation Problem, without Dark Matter

Robittybob1 said:
In a situation where you could be getting length contraction without motion, it teases your understanding.
I was worried that I haven't made myself clear but "I propose that the difference in distances is amount of length contraction in a region of GTD" explains it quite well. Light has to travel a longer distance to go across the lift. To account for that longer time over a distance it is explained as length contraction and time dilation. I must admit I'm struggling to see what would make the lift get narrower.
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I'll try and make a stand, even though I'll admit I'm doing it tentatively, I'll say "Gravitational time dilation is associated with length contraction only in the direction of the apparent equivalent acceleration". There is no change to the width of the rocket or the lift (or whatever describes your non-inertial frame). The distance that the light beam has to go across the frame does not change but there is a change in the length along the axis describing the gravitational acceleration.
Now how could we prove that?

The other thing that has me baffled is that if Gravity is equivalent to upward acceleration (take the Earth ) 1 g.

Now in space if something had acceleration equivalent to 1* g, it would get up to near light speed after a while, but the person on the Earth in the same equivalent acceleration is still locked on to the Earth, and hasn't moved an inch.
 
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Robittybob1 said:
I'll try and make a stand, even though I'll admit I'm doing it tentatively, I'll say "Gravitational time dilation is associated with length contraction only in the direction of the apparent equivalent acceleration". There is no change to the width of the rocket or the lift (or whatever describes your non-inertial frame). The distance that the light beam has to go across the frame does not change but there is a change in the length along the axis describing the gravitational acceleration.
Now how could we prove that?
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It seems as if what you are saying is that where gravitational time dilation (GTD) is involved, the associated length contraction is only in the direction of the gravitational force...? And not in any direction say at 90 degrees to a gravitational force?

That raises an issue with the speed of light itself. We do know that a clock is GTD, running faster the further it is from a gravitational center of mass. If length contraction only occurrs in the direction of the gravitational force, any measurements of the speed of light, in the direction of the gravitational force and, again say at 90 degrees to that force, and measured using the same clock, would not agree. The speed of light would vary in a gravitational field relative to what direction through the field it was traveling... And the speed of light while universally constant within the context of SR, would be infinitely variable within the context of GR.
 
OnlyMe said:
It seems as if what you are saying is that where gravitational time dilation (GTD) is involved, the associated length contraction is only in the direction of the gravitational force...? And not in any direction say at 90 degrees to a gravitational force?

That raises an issue with the speed of light itself. We do know that a clock is GTD, running faster the further it is from a gravitational center of mass. If length contraction only occurs in the direction of the gravitational force, any measurements of the speed of light, in the direction of the gravitational force and, again say at 90 degrees to that force, and measured using the same clock, would not agree. The speed of light would vary in a gravitational field relative to what direction through the field it was traveling... And the speed of light while universally constant within the context of SR, would be infinitely variable within the context of GR.
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We seem to be discussing science which isn't covered often elsewhere so we may not get it right the first time, but so far it seems to hold true.
Stronger the field the slower the time (black hole time stops - that keeps us in the right alignment, so out in space away from gravity time runs the fastest). So out in space the light clock will bounce light directly across the frame. That is the shortest distance from one side to the other so ticks are fastest.
Near a strong gravity field the light will take a curved path across the frame, a curve is longer than a straight line, the more curved the slower the time. But at all times the width doesn't change just the amount of displacement in the direction of the field.

If the light clock was operated in the "direction of the field" the light doesn't curve or slowdown/speed up but changes frequency (blue-shift toward the gravity source, red-shift when headed away). So to get the light clock to slow when in the stronger field the length of the frame must alter. But which way does it alter?

To slow down time in a strong field the frame would have to lengthen! Completely the opposite to my initial logical thinking (it is not like the frame is squashed), but the logic is OK when the words "tidal forces" are used. So the bottom of the frame is being stretched away from the top so the frame lengthens. (even when the frame is resting on a surface. Now that is hard to imagine).

I get the feeling what I've said is pretty correct. Do you agree?
 
Robittybob1 said:
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If the light clock was operated in the "direction of the field" the light doesn't curve or slowdown/speed up but changes frequency (blue-shift toward the gravity source, red-shift when headed away). So to get the light clock to slow when in the stronger field the length of the frame must alter. But which way does it alter?

To slow down time in a strong field the frame would have to lengthen! Completely the opposite to my initial logical thinking (it is not like the frame is squashed), but the logic is OK when the words "tidal forces" are used. So the bottom of the frame is being stretched away from the top so the frame lengthens. (even when the frame is resting on a surface. Now that is hard to imagine).

I get the feeling what I've said is pretty correct. Do you agree?
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I'm struggling with the thought of the frame being longer in a strong G field. Stand on a Neutron star are you going to get taller? I doubt it so what makes the light clock slow? Are you going to tell me the speed of light isn't constant, for that is the other way to slow the clock?
Either lengthen the frame or slow the speed of light.
Can strong gravity slow the speed of light? For the alternative of lengthening a frame near a strong G force seems out of the question too.
 
Can strong gravity slow the speed of light? Wasn't this one of the classic experiments - Light slowed when passing massive bodies?
The Shapiro time delay effect, or gravitational time delay effect, is one of the four classic solar system tests of general relativity. Radar signals passing near a massive object take slightly longer to travel to a target and longer to return than they would if the mass of the object were not present.
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This YouTube covers a lot of what we have been discussing "Relativity 10b - uniform gravity/acceleration II"
http://www.youtube.com/watch?v=4mTD9hpIyMk
 
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Robittybob1 said:
I'm struggling with the thought of the frame being longer in a strong G field. Stand on a Neutron star are you going to get taller? I doubt it so what makes the light clock slow? Are you going to tell me the speed of light isn't constant, for that is the other way to slow the clock?
Either lengthen the frame or slow the speed of light.
Can strong gravity slow the speed of light? For the alternative of lengthening a frame near a strong G force seems out of the question too.
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I think you are thinking properly, though I am not willing to conclude anything as yet I have some thoughts to add.

The reason I think I was saying that any contraction must be in three dimensions (for lack of better understanding of visualizing the fourth) is because of how you put it; that length contraction would only happen perpendicular to the surface of a planet; only opposite the centralized tidal forces, but not necessarily along the surface. If contraction occurs only in this outward fashion, then it is contracting nearly equally toward all escaping objects of the full 129,600 degrees of a sphere. 360’ X 360’ radially.

If contacting in this fashion than the whole sphere is contracted, therefore the length across the surface of the mass is also shortened. There is really no other mathematical solution. If that is so, it would shorten the distance travelled across the surface of such a planet as well, making our measure of speed, or time, equal with the slower tick, in a heavier Gravitational field, from the 'slow ticking observer frame' defined by Einstein. I think that cannot be. Remember that all relative Gravitational frames agree who is slowing down and who is speeding up. There must be a difference in time. We don't have an equation for length contraction yet, do we?

Think one more time about our orbital period of the nice lady on our supermassive planet. If there was a geometric physical contraction of the planet we observe from here, then we would not be able to see this equation of the slower clock in effect. All would appear equal, with no slow ticking, or factual ticking, observer. Even if we were to accept this, the meter is measured by the speed of light as well, over a certain distance within a time, so the meter would appear equal, again equaling... to zero time dilation.

We can consider how this might affect the common (pop Science) conception of simple length contraction in SR, but I think that neither can be geometrically true, if Time Dilation is true; that time can bow to the speed of light, mass, geometry, and G….. I think we must agree that time does so, and nothing else.
 
Scott Myers said:
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Think one more time about our orbital period of the nice lady on our supermassive planet. If there was a geometric physical contraction of the planet we observe from here, then we would not be able to see this equation of the slower clock in effect. All would appear equal, with no slow ticking, or factual ticking, observer. Even if we were to accept this, the meter is measured by the speed of light as well, over a certain distance within a time, so the meter would appear equal, again equaling... to zero time dilation.

We can consider how this might affect the common (pop Science) conception of simple length contraction in SR, but I think that neither can be geometrically true, if Time Dilation is true; that time can bow to the speed of light, mass, geometry, and G….. I think we must agree that time does so, and nothing else.
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@ Scott - I followed your logic up to where you start talking of this supermassive planet. In the post http://www.sciforums.com/showthread...-Dark-Matter&p=3048831&viewfull=1#post3048831 you talk of "supermassive" is that the situation or was there another?

And your conclusions were a little rough as well. I missed your logical steps. So you are not into length contraction, right!
 
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Scott Myers said:
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If contacting in this fashion than the whole sphere is contracted, therefore the length across the surface of the mass is also shortened. There is really no other mathematical solution. If that is so, it would shorten the distance travelled across the surface of such a planet as well, making our measure of speed, or time, equal with the slower tick, in a heavier Gravitational field, from the 'slow ticking observer frame' defined by Einstein. I think that cannot be. Remember that all relative Gravitational frames agree who is slowing down and who is speeding up. There must be a difference in time. We don't have an equation for length contraction yet, do we?
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"Remember that all relative Gravitational frames agree who is slowing down and who is speeding up." Not according to the videos I've seen. Acceleration is thought to be the Universe being pulled back by gravity. So if you think the Universe is accelerating when it is really you how can you say "that all relative Gravitational frames agree who is slowing down and who is speeding up"?

If the sphere we are standing on is somewhat compressed by length contraction and in all directions that will be no different than what is actually happening. The density of the core of the Earth is a higher density than the same material at normal air temp and pressure. So the material will be tighter packed in all dimensions. So if this gravity causes compression how do you get the light clock to tick slower? If the distances are shorter the mirrors are closer and time speeds up not slows down.
So the speed of light must be even slower still so there is slowing of time in a strong gravitational field. Did the Shapiro effect demonstrate this? The Shapiro isn't a bending of light is it? Yet in Wikipedia it looks like they are calculating a curvature.
 
I will write to WaiteDavid and see if he can explain Shapiro Delay to me.
If Shapiro Delay is just due to the light having to travel a longer route that does not mean light slowed down at all. I want to see if light travels slower when it moves away from a gravitational mass.

In the classical rocket ship situations where they have fired a light beam and then they accelerate to catch up with the light beam it would in a way seem that the light appears to have slowed down for the light will not be advancing as fast away from the ship.
When this acceleration is thought to be due to a gravitational field, it then is concluded the reduced speed of light is due to this gravitation.
I think there is a flaw in this reasoning (when this acceleration is thought to be due to a gravitational field, it then is concluded the reduced speed of light is due to this gravitation) for why would the gravitation NOT be attracting the base that one is standing on as well?
http://www.youtube.com/watch?feature=endscreen&v=ev9zrt__lec&NR=1 go to about 11:44 through the video and see the section I'm talking about.
The phrase at 12:17 must be erroneous. "His spaceship standing still and the rest of the Universe which is accelerating." I could accept that if he wasn't thrown back into his seat, but he is thrown back in his seat so the ship is accelerating, for how was he going to reason his ship was able to stand still?
That is a flaw in the reasoning of relativity. It isn't the only one I have noted thus far in my research into these thought experiments, but this is the first time I've been sure of it.
 
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"For how was he going to reason his ship was able to stand still?" That is the question that is bugging me at the moment.
Previously the ship was standing still and the universe was passing by, he knows his rockets are providing forward thrust but how does he know his ship was able to remain standing still?
 
Robittybob1 said:
"For how was he going to reason his ship was able to stand still?" That is the question that is bugging me at the moment.
Previously the ship was standing still and the universe was passing by, he knows his rockets are providing forward thrust but how does he know his ship was able to remain standing still?
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I suppose it is just the same misconception that anyone has thinking they are stationary and everyone else is moving around them. Therefore by that same illusion he knows his rockets are providing forward thrust and he knows his ship is able to remain standing still.
Mind you it could be true, and if there truly is no way of disproving it, I just have to accept it.
 
Robittybob1 said:
I suppose it is just the same misconception that anyone has thinking they are stationary and everyone else is moving around them. Therefore by that same illusion he knows his rockets are providing forward thrust and he knows his ship is able to remain standing still.
Mind you it could be true, and if there truly is no way of disproving it, I just have to accept it.
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That Shapiro Time Delay seems hard to get your head around too! In a region of stronger gravity time slows but they quickly make a point that light will still travel at c in the local frame yet they notice that light slows down going near the same region. Does that imply a person in an region of gravitational time dilation will not notice time is slowed , and that light is slowed for it still travels at c? The same distance in the same amount of time? If the speed of light is slower that can only be achieved if distance is length contracted, so what happens when you add time dilation to that mix? The "same" distance in greater amount of time, the speed of light is even slower that can only be achieved if length is even more contracted???? Can any of that make sense? Do you stay young, like the traveling twin in the Twin Paradox, if you go to a region of severe gravitational time dilation?
I could imagine it won't be that comfortable weighing 1000's of times heavier than on the Earth. The blood would drain from your head even if you were lying down. Doesn't sound like you'd live long.
 
WaiteDavid replied to me on another forum http://www.physforum.com/index.php?act=Post&CODE=06&f=30&t=44897&p=591011
where φ is the Newtonian gravitational potential taken to be zero at infinity where the hypothetical remote observer for which these coordinates are appropriate is. Using the line element to describe the spacetime path of an observer somewhere else you get
dcτ² = (1 + 2φ/c²)dct² + ...
If that observer is not moving with respect to the remote observer coordinates then you get
dct = dcτ/√(1 + 2φ/c²)
which is called gravitational time dilation.
Unfortunately I haven't felt confident to try and put these figures into a particular situation and see what it all means. We had previous examples of GTD so maybe we could try and get the same results again.
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My brain is struggling on this GTD and Shapiro Time Delay, it doesn't seem to come to a quick understanding of it.

Now I think I have made a mark in the sand, now could the following be true? A photon travelling through space-time no matter which direction it was going, it experiences the same gravitational potential at that point regardless of the direction it was going.
Prior to this I might have treated those that are heading straight to the source of gravity (Pound-Rebka experiment), or away from the source differently to those that were travelling through the region or passing by the gravitational source (as in the Shapiro experiments).
So in the Pound-Rebka experiment when light was dropped in a gravitational field and it had a higher frequency at the bottom of the tower, the same photons fired at the target coming from any direction from the same source, in the same gravitational potential, would have had the same target frequency??? Like, I'm saying the same results would be found in the Leaning Tower of Pizza as much as a tower at the university, and tipping that tower over further would not alter the frequency of the photons at the base.
 
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Robittybob1 said:
My brain is struggling on this GTD and Shapiro Time Delay, it doesn't seem to come to a quick understanding of it.

Now I think I have made a mark in the sand, now could the following be true? A photon travelling through space-time no matter which direction it was going, it experiences the same gravitational potential at that point regardless of the direction it was going.
Prior to this I might have treated those that are heading straight to the source of gravity (Pound-Rebka experiment), or away from the source differently to those that were travelling through the region or passing by the gravitational source (as in the Shapiro experiments).
So in the Pound-Rebka experiment when light was dropped in a gravitational field and it had a higher frequency at the bottom of the tower, the same photons fired at the target coming from any direction from the same source, in the same gravitational potential, would have had the same target frequency??? Like, I'm saying the same results would be found in the Leaning Tower of Pizza as much as a tower at the university, and tipping that tower over further would not alter the frequency of the photons at the base.
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So we are now looking for a way to account for the extra length without making it physically longer. So I can see a possibility here in that when there is a gravitational blue-shift we still have the same number of wave-crests for the starting frequency. frequency * wavelength = speed so with the light falling its speed would have gone beyond c but is bound by c the but it has a type of "imaginary velocity" component which is also travelled in an "imaginary length". So when the light is viewed it looks as if its frequency is faster, but c is still c, for some of the distance it travelled was in "imaginary space-time".
So looking from a remote location, light and time will be slowed, so you observe both GTD and Shapiro Time Delay, for the actual distance that the light has travelled is longer for some of the time the photons were travelling in the "imaginary space-time".
Now this may seem bizarre but it is early days yet, for I have been struggling for weeks now to see where the GTD could get its extra distance from, and where the photons falling were getting their extra energy from, and how to account for the Shapiro Time Delay, and no one has helped me except for WaiteDavid.
 
I've gone back to the basics and I'm working through the series on Relativity by "PhysicistMichael" starting with General Relativity: 1 - Issues with Newtonian Gravity
http://www.youtube.com/watch?v=d95I3ka6DXU

10 -14 minute sessions excellent and very educational, but you need a few spare hours to go through them all but he starts from the basics and works up from there.
 
This interesting article appeared on Google News today
"Starwatch: What's the dark matter?"
http://www.guardian.co.uk/science/2013/jul/14/starwatch-dark-matter-galaxies-particles-gravity

Gravity, too, binds most galaxies into groups or clusters. As long ago as 1933, the Swiss astronomer Fritz Zwicky recognised that the total mass of the visible material, the stars, gas and dust, in the Coma cluster of galaxies appeared insufficient to hold the galaxies together given their observed relative velocities. Without the additional gravitational pull of something he termed "dark matter", the cluster, and countless others, would simply dissipate and disappear as the galaxies flew apart.
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