# This is an SR effect (split from Universal Concept of Time (Is the Big Bang wrong?))

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On 1/29/2020 at 2:50 AM, lucien216 said:

"It is the same event, but different amounts of time have elapsed since then as measured by different observers. "

Hhhhmm. This is what I wanted to hear. So you saying that the universe could be, say 30 billion years old, for some observers? So the age of the universe is only relative to us then?

On 1/29/2020 at 3:12 AM, Strange said:

Yes, in principle.

In fact, our view of the universe is pretty average so it would be hard for any observer to have seen a significantly greater age for the universe than us.

Quite plausible actually, not just in principle.  In the inertial frame X of some planet in a galaxy 27 billion light years from here (distance measured in frame X), the universe is currently (simultaneous with us now) about 30 billion years old.

On 1/29/2020 at 3:54 AM, studiot said:

It is more subtle than this.

The 'Universe' for such an observer would be quite different from the 'Universe' we can see.

...

We do not know of any observer (star etc) going at sufficient relative speed to us to observe 30 billion years.

Yes, the universe for such an observer would be quite different from what we see here since for one thing it appears to be over twice as old. Much more mature galaxies and such.

Yes, we do know of galaxies moving at sufficient speed for this. The one I mention above would have a redshift of about z=1.3 as viewed from here, and the record holder is over z=11.

Yes, I realize I'm replying to posts from January, before I registered I think.

Edited by Halc
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5 minutes ago, Halc said:

Quite plausible actually, not just in principle.  In the inertial frame X of some planet in a galaxy 27 billion light years from here (distance measured in frame X), the universe is currently (simultaneous with us now) about 30 billion years old.

I’m not sure what definition of “simultaneous” you are using. I can’t imagine one that would make this statement true. For any reasonable definition of simultaneous, the observers would both see the universe being about 13.8 bn years old.

10 minutes ago, Halc said:

Yes, we do know of galaxies moving at sufficient speed for this. The one I mention above would have a redshift of about z=1.3 as viewed from here, and the record holder is over z=11.

Red shifts do not correspond to speeds. Otherwise there would be a problem with the galaxies we see with recessional velocities greater than c.

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1 hour ago, Strange said:

I’m not sure what definition of “simultaneous” you are using. I can’t imagine one that would make this statement true. For any reasonable definition of simultaneous, the observers would both see the universe being about 13.8 bn years old.

Red shifts do not correspond to speeds. Otherwise there would be a problem with the galaxies we see with recessional velocities greater than c.

I'm using the SR definition.  They're stationary, we're moving fast enough in their frame that 30 years dilates down to 13.8, which is somewhere around 0.9c.  So I picked a galaxy relative to which we're moving away at that speed, and if we see 13.8 GY with our dilated clocks, they must see 30 GY.

Yes, it is a stretch to use special relativity at such a non-local scale.  Times over cosmological distances are never considered in our inertial frame (they use a comoving frame), which is why it sounds strange to consider a frame where the age of the universe is 'currently' much more than the figure we usually hear.

Red shifts of galaxies do very much correspond to speeds.

The shift-to-speed conversion (consensus is near the .3, .7 line) only works with objects with negligible peculiar velocity, which is true of any galaxy, but not true of the space ship receding from Earth at 0.9c, the speed of which would follow the SR line to the lower right.  The v=cz is Newtonian physics.

OK, the graph above is admittedly a graph of recession speed in comoving coordinates, not inertial coordinates. That means it is the rate at which the proper distance between us and them increases per unit of comoving time. That's pretty different than the inertial definition, the increase per unit of inertial time.  Point is, there is very much a galaxy relative to which we're moving at 0.9c, even if I computed its redshift incorrectly.

Edited by Halc
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10 hours ago, Halc said:

I'm using the SR definition.  They're stationary, we're moving fast enough in their frame that 30 years dilates down to 13.8, which is somewhere around 0.9c.  So I picked a galaxy relative to which we're moving away at that speed, and if we see 13.8 GY with our dilated clocks, they must see 30 GY.

Stationary with respect to what? Why isn't the kinematic dilation symmetric?

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1 hour ago, swansont said:

Stationary with respect to what? Why isn't the kinematic dilation symmetric?

Stationary relative to the inertial frame in which they are stationary.

It is completely symmetric. In their frame, we're moving fast and our clock says it's been 13.8 GY since the BB, instead of 30.  In our frame, when our clock says the universe is 30 GY old, their fast moving clock will read 13.8 GY. That's simple relativity of simultaneity.

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10 minutes ago, Halc said:

Stationary relative to the inertial frame in which they are stationary.

It is completely symmetric. In their frame, we're moving fast and our clock says it's been 13.8 GY since the BB, instead of 30.  In our frame, when our clock says the universe is 30 GY old, their fast moving clock will read 13.8 GY. That's simple relativity of simultaneity.

But our clock doesn't say the universe is 30 GY old, it says 13.8 GY (and their clock runs slow, not fast) but theirs will also say it's 13.8 GY. That's not what we would see their clock saying if this were a SR effect, which it isn't.

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13 hours ago, Halc said:

I'm using the SR definition.

You can’t use that on cosmological scales. You have to use GR. (Apart from all your other errors that have been pointed out.)

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2 hours ago, swansont said:

But our clock doesn't say the universe is 30 GY old, it says 13.8 GY (and their clock runs slow, not fast) but theirs will also say it's 13.8 GY. That's not what we would see their clock saying if this were a SR effect, which it isn't.

Your statement implies a preferred moment.  A clock is a worldline and it reads all times along that worldline and doesn't say that the universe is any one particular time.

1 hour ago, Strange said:

You can’t use that on cosmological scales. You have to use GR. (Apart from all your other errors that have been pointed out.)

Yes, this is a better destruction of my argument. As I said above, it is quite a stretch to use SR on the scale I chose.  There are empirical differences (such as the angular size of rapidly receding objects) that falsify the SR view on those scales.  I was just trying to illustrate a coordinate system that put our current event simultaneous with an event with a clock that measures 30 GY since the BB.

I don't think you pointed out any blatant errors before. Redshifts do actually map to speeds. Galaxies don't recede at superluminal speeds under SR where velocities add via the relativistic rule instead of the simple addition that is commonly used at cosmological scales.  The entire universe could be mapped in an inertial frame iff expansion was forever constant (inertial), but it isn't.  It was decelerating and now it is accelerating, which forms an event horizon that cannot exist in a flat SR model. That right there falsifies the model. I'm not asserting that what I've done is legal.

As for GR, not even GR suggests a way to foliate all of spacetime, something I pointed out in rjbeery's thread. I can have an observer that asks the question: "What is the age of the universe now?" and GR gives no meaningful reply to the question.

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34 minutes ago, Halc said:

Your statement implies a preferred moment.  A clock is a worldline and it reads all times along that worldline and doesn't say that the universe is any one particular time.

No, my statement is about what our clock reads. we are observers at some coordinates, and the time coordinate is not multivalued.

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On 7/14/2020 at 4:23 PM, Halc said:

I don't think you pointed out any blatant errors before.

No, but others have.

On 7/14/2020 at 4:23 PM, Halc said:

As I said above, it is quite a stretch to use SR on the scale I chose.

For "quite a stretch" read: "wrong".

On 7/14/2020 at 4:23 PM, Halc said:

I was just trying to illustrate a coordinate system that put our current event simultaneous with an event with a clock that measures 30 GY since the BB.

And failed. You are using the wrong theory and, as others have pointed out, using it incorrectly.

On 7/14/2020 at 4:23 PM, Halc said:

Redshifts do actually map to speeds. Galaxies don't recede at superluminal speeds under SR where velocities add via the relativistic rule instead of the simple addition that is commonly used at cosmological scales.

This is inconsistent. If red-shifts map to speeds then we do see galaxies receding at superluminal speeds. if you say they are not receding at speeds greater than c, then red-shifts do not correspond to speed. (This is one of the problems that arises when you try to interpret the red-shift as a Doppler effect.)

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On 7/15/2020 at 6:39 PM, Strange said:

For "quite a stretch" read: "wrong".

No argument there.  But since they made my own topic out of this diversion, I might as well defend what I'm doing.

Can I edit the topic title?  I never said anything on the order of "This is an SR effect".  More like "How the universe could be 30 GY old".

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You are using the wrong theory and, as others have pointed out, using it incorrectly.

I may be using the wrong theory, but I'm wielding it correctly. Using the wrong theory gets me some empirical contradictions, but nobody has pointed out any of them.  I think perhaps we can explore some of them.  You can tell me precisely where I'm using the theory incorrectly.

The universe can be described by an inertial frame iff expansion was inertial (the scalefactor was linear). The scalefactor function isn't linear, so the theory is misapplied. No argument there.

I'm considering the universe only in a local context. I just drew an unusually large box around my system. In such a coordinate system, the big bang happened at the origin of the inertial frame, the location where a comoving object is stationary.  Everything is moving away at a rate that is a linear function of its distance, up to the speed of light.  A Lorentz transformation can be applied making any point in space that center of the universe, so there is no preferred location until an inertial frame is chosen.

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This is inconsistent. If red-shifts map to speeds then we do see galaxies receding at superluminal speeds.

The graph I showed has superluminal speeds. It measures speed as comoving proper distance per unit time, and that kind of speed accumulates additively, not relativistically, so you get speeds arbitrarily high. By accumulating additively, I mean if I observe Bob in his galaxy receding at 0.6c, and Bob is looking at Charlie in the same direction receding from Bob at 0.6c, then I am going to observer Charlie recede at 1.2c, not 0.88c.  Under SR rules, Bob is receding at 0.54c from me and Charlie is moving at 0.83c.  Different coordinate systems yield different speeds.  The graph I showed plots the redshift to speed conversion for both coordinate systems as well as a few others. Redshifts have always mapped to speeds, even if it took a lot of (ongoing) work to generate that graph.  Also note that the graph shows redshift to current recession speed, not recession speed at the time of emission of the light we're measuring.  Under the SR system, the two speeds are the same because I'm ignoring the expansion rate changing, which is one of the ways SR is wrong.

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if you say they are not receding at speeds greater than c, then red-shifts do not correspond to speed.

Sorry, but the line is drawn for SR as well.  The speed of a spaceship leaving Earth can be measured by its redshift.

So what are some empirical problems with doing what I'm doing?  For one, there is no event horizon under SR, so light can get here from anywhere given enough time. This is true if expansion is not accelerating, and I said I was ignoring expansion rate changes, and besides, you can't empirically see the event horizon. We see plenty of objects that have long since passed beyond it.

A big problem is the angular size of galaxies. Under SR, the faster something is receding, the further away it is from us when the light we see now is emitted, and the galaxy appears smaller much in the same way that Saturn appears smaller than Jupiter when they're more or less aligned like they are not.  Not so under the standard model. GN-z11 for instance (redshift z=~11) appears twice the angular size as a similar size object with redshift 2, because the light from it was emitted from half the proper distance from here compared to the lower redshift galaxy. SR just cannot account for that appearance.

Light travel time is also significantly different, but that cannot be directly measured, so I'm not sure if it counts as an empirical difference.  Observing gravitational effects like lensing is an obvious difference between SR and GR, but I'm not suggesting otherwise. I'm assuming that on a large scale, the universe is essentially flat.

I drew a crude picture of the universe using inertial coordinates, and except for the constant expansion rate, it pretty much worked. I can post it if you like. It had a finite size (an edge), but was nevertheless everywhere isotropic to any observer.  The angular-size thing really sinks it, because I couldn't immediately think of other immediate empirical problems.  If you put our solar system way off center in the picture, you can make the current age of the universe as old as you like, and that's what I was doing when I made my initial comment which is its own OP now.

Edited by Halc
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6 hours ago, Halc said:

I'm assuming that on a large scale, the universe is essentially flat.

Under the FLRW model, when we say that the universe is ‘flat’ (one of three possibilities, depending on the choice of the k parameter), then what is meant is the Gaussian curvature. But this is only one isolated aspect of the geometry of the manifold (roughly equivalent to the average spatial curvature) - the complete description of the geometry is given by the Riemann curvature, which is never zero in the FLRW model. How could it be? It is an interior solution to the field equations after all.

So essentially, for FLRW cosmology, the Riemann tensor doesn’t vanish:

$R{^{\mu}}{_{\nu \lambda \delta}} \neq 0$

But in order for a region of spacetime to fall under the dynamics described by SR, it has to be Riemann-flat:

$R{^{\mu}}{_{\nu \lambda \delta}}=0$

This means you can’t use SR to describe the universe at large. The FLRW spacetime can be spatially flat in a Gaussian sense, but its geometry is never Minkowskian, as is required for SR to apply.

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In essence correct the FLRW metric is however in the weak field limit so SR is still useful. The slight curvature will cause deviations at extreme ranges however is approximately flat for the shorter ranges.

Past the Hubble horizon the deviations become apparent. The recessive velocity and Z scale will become more progressively non linear. ( In order to correct for this one must take into account the evolution of the matter, radiation and Lambda densities)

The updated  cosmocalculator has that capability see signature.

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13 hours ago, Mordred said:

The slight curvature will cause deviations at extreme ranges however is approximately flat for the shorter ranges.

Indeed - which is trivially true for all spacetimes, only the magnitude of the ‘range’ changes

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