# Time Dilation and Absolute Age of the Universe

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#### rpmath

##### Guest
FlatEarth":xptwcj51 said:
1) The example is often given that if a spaceship moves away from Earth, the occupants will age at a slower rate than those who remain on Earth. Who is to say that the opposite won't happen? What if the craft travelled in a direction that gave it a slower absolute speed than Earth's? I believe the opposite would be true. People on Earth would age more slowly than those on the spaceship.
In relativity there is way to know our "absolute speed", the theory says there are no such things as "absolute speed" or "absolute time".
You can not say what is happening in other point of the universe at the same time, because there is no absolute "same time" unless both objects are at the same point of the space.

The big bang gives us a speed I interpret as an absolute one, but it is some sort of heretic concept to many scientists...
there is even a theory that says the effect in microwave background that is easily represented as earth having an speed relative to the background of near 600 km/s is really the effect of being near the center of a space-time bubble or something like that.

If you go slower than earth in some direction, then you will need to go faster to reach earth again.

The longer the path some one travels between 2 points of space-time, the shorter the time he measures.

But the earth loops around the sun, so there is a shorter path:
- Launch a rocket at 30 km/s (0.0001 c) in the opposite direction of earth translation to stop orbital speed.
- Keep it fixed relative to the sun compensating sun gravity with the rocket.
- Wait 1 year for earth returning to the same place.
One clock in the rocket will mark 1/sqrt(1-v/c) = 1.000000005 times what a clock in the earth marks
in 365.25 days of 24 hours of 3600 sec = 31557600 sec
the difference will be 0.000000005 * 31557600 = 0.157788 sec
it is small, less than 1/6 sec ...
but will be more than a clock on earth.

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#### FlatEarth

##### Guest
Hello, Kessy. I did review the Wiki page and I admit it is different from my previous understanding of relativity. I have always considered relative speed alone and not acceleration to be the key factor, and thus I join you and the others in sharing a common understanding of time dilation (but reluctantly). To really understand it, I need to understand why acceleration is key. Wish me luck.

A number of good posts here helped me with my understanding. Thanks to all. Now who wants to go on my starship? I can now pretty much guarantee you will not come back prematurely older.

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#### whitecrowro

##### Guest
Yes, relativity..
Time is a measure of distance vs speed . Let's discuss the 'distance'.
Distance means 2 distant points. Gravity involvement based on relativity means that space is warped in a bubble
around masses. Due to the different position of the two watches and the Heisenberg principle it is impossible to match the two watches, or to reference them to each other. A 3rd location would be again useless.
The simplest way to measure would be to consider center of bubbles as different points on a string; and that was calculated. But remember that our measurable time is the time we 'walk' on the surface of our 'individual' sphere.
If the initial uni-space, uni-(non) time singularity was simple enough, the afterward expanding soup of bubbles interacting and interfering to each other is getting time and space much beyond our (theoretical also) capabilities with every 'relative' time that passes.

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#### odysk9

##### Guest
On a much simpler question, I frequently wonder (apparently I don't have enough to worry about) that if the universe is apparently the same in every direction we look, we can see back to about 13 billion years - say to the EAST, and then look WEST another 13 billion years, wouldn't that place us in the center of the universe, which would then span some 26 billion years? While I find all the plans to look farther and farther back in time by designing and implementing ever more advanced telescopes, I still wonder the universe's true age. Also, if it took some 13 billion years for light to reach us from any direction you choose, doesn't it indicate that we were some 13 billion light years away from the light source 13 billion years ago? Also, hasn't our relative position (or distance) from those 13-billion-light-years-away objects increased?
Would love it if anyone could explain this to me.

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#### MeteorWayne

##### Guest
Yes, the observable universe is a bubble 13 billion ly in all directions. The whole Universe extends beyond that distance, but we can't see those parts because they are farther away than the light has had time to travel; and due to the expansion of the Universe, those parts are moving even further away.

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#### BuzzLY

##### Guest
chrisWin":1qj1cg76 said:
I have another problem similarly related (excuse pun!)
We have worked out that from our view point the Universe is roughly 13.7 Billion years old . The cosmologists there for tell us we can only study the visible Universe (going back time further we look!) but the Universe is obviously somewhat bigger that the visible hence why we appear to be in the middle of it no matter what telescope is used . Now here`s my problem the speed of light restricts what we see however if the universe started from a single point exploding outwards how does it become bigger than 13.7 Billion light years across as nothing in the Universe can go faster than light ? I know it probably has something to do with time dilation but I`ve never seen anything that explains this and how.
While it is true that nothing travels faster than the speed of light, "c" so on the suface the diameter would seem to only be 13.7 bn LY accross ... or some might tguess 2c since light would travel out in both directions from the original singularity. However, what many don't factor in is that since the big bang space itself is expanding. I've heard that the current estimate of the diameter of the universe is somewhere near 157 bn LY and includes the expansion of space. The key issue as I said is the expansion of space.

To respond to another comment that suggested that to experience a time dialation you'd need to be "inside a singularity." Actually, you only have to be near a gravitational source to get a dialation. Time moves slower here on the surface of Earth than it does 200 miles up in earth orbit. I would think that anywhere within the fillaments of the comic web time would be slower than in the voids. I often wonder (since I've read that dark energy is strongest in the voids) if dark energy itself is not just the observation of this void/fillament time dialation. Irregardless, since time is faster in the voids, so the voids are "older than" the matter filled fillaments ... and accordinly, have had longer for the space within to expand.

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#### FlatEarth

##### Guest
odysk9":1z6dpfsn said:
... Also, if it took some 13 billion years for light to reach us from any direction you choose, doesn't it indicate that we were some 13 billion light years away from the light source 13 billion years ago? Also, hasn't our relative position (or distance) from those 13-billion-light-years-away objects increased?
Would love it if anyone could explain this to me.
Well, obviously I've proven that I am no expert on the subject, but I think I can answer this question. Objects that are measured to be 13 bly away actually were much closer when light originally left them. Also, they are now much further away than 13 bly. There are calculators available on the Internet that use the redshift value to figure out the two distances. Here are two:

http://www.icosmos.co.uk/

http://www35.wolframalpha.com/input/?i=redshift z%3D0.5

If I am using the calculators correctly, they indicate that a super nova with a redshift of 8.2, or 13 bly away, was about 3.1 bly away at the time it exploded, and today is 30 bly away.

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#### mabus

##### Guest
odysk9":19vqdoik said:
On a much simpler question, I frequently wonder (apparently I don't have enough to worry about) that if the universe is apparently the same in every direction we look, we can see back to about 13 billion years - say to the EAST, and then look WEST another 13 billion years, wouldn't that place us in the center of the universe, which would then span some 26 billion years? While I find all the plans to look farther and farther back in time by designing and implementing ever more advanced telescopes, I still wonder the universe's true age. Also, if it took some 13 billion years for light to reach us from any direction you choose, doesn't it indicate that we were some 13 billion light years away from the light source 13 billion years ago? Also, hasn't our relative position (or distance) from those 13-billion-light-years-away objects increased?
Would love it if anyone could explain this to me.

Great questions. The problem with your first question is that you assume that what we see is the entire universe. Let's assume the universe is larger than what we see (and we know this to be true). To answer this more easily let's take a completely fictional and hypothetical universe that is 100 bly across (just to have a number that is easy to work with and in no way tied to reality). The 26 bly stretch we can see could be anywhere along this 100 bly long line couldn't it?

In fact the universe may be much much larger than even this, it may be 100 bly, or it may even be 100,000,000,000 bly, or it may be a billion trillion times that size. We just don't know. In that context, the puny 26 bly across that we can see seems rather insignificant, and isn't likely to be the center of anything.

As to your second question, yes, the objects are moving and have moved since the light we recieve has left them. When we recieve light from something we see the way the object was at the time the photons left the object. Our sun for example, is about 8 light minutes away from the earth. If the sun exploded right now, we would not see the explosion for a full 8 minutes before the light emited during the explosion finally reached us. Similarly, when we see a galaxy 5 billion light years away, we see it as it was 5 billion years ago, and so on.

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#### darkmatter4brains

##### Guest
ramparts":2k6bbxi6 said:
SpeedFreek":2k6bbxi6 said:
Cosmological time (and the age of the universe) is an approximation, based on a theoretical series of clocks in free-fall across time, under the least gravitational influence in their own epoch, co-moving with the expansion of the universe.

Beautifully put!

ah yes, and this reminded me how this is all related to the CMB!

When measured from Earth, the CMB (Cosmic Microwave Background) Radiation does look a tad warmer in one direction than it does in the other. This is because Earth is not perfectly comoving with the expansion of the Universe. It's in orbit around the Sun; The Sun "orbits" around in the Milky Way galaxy on one of the rings. And, the Milky way even has some overall motion towards the Hydra cluster.

The CMB exhibits the highest degree of homogeneity (and isotropy, really) in the frame that is comoving with the expansion of the Universe. Any measured change in this homogeneity would indicate that the frame from which you have measured it in, has some motion away from the expansion of the Universe.

The fact that the CMB is homogenous across the entire Universe, lets us be able to confidently define an age for the Universe that EVERYBODY, ANYWHERE can agree upon. Almost sounds "absolute" doesn't it!!

Actually, it almost sounds like the ether. But, not quite, thank goodness

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#### SpeedFreek

##### Guest
FlatEarth":1ykcauw3 said:
Well, obviously I've proven that I am no expert on the subject, but I think I can answer this question. Objects that are measured to be 13 bly away actually were much closer when light originally left them. Also, they are now much further away than 13 bly. There are calculators available on the Internet that use the redshift value to figure out the two distances. Here are two:

http://www.icosmos.co.uk/

http://www35.wolframalpha.com/input/?i=redshift+z%3D0.5

If I am using the calculators correctly, they indicate that a super nova with a redshift of 8.2, or 13 bly away, was about 3.1 bly away at the time it exploded, and today is 30 bly away.

Excellent post!

Here is another calculator:

http://www.astro.ucla.edu/~wright/CosmoCalc.html

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#### ramparts

##### Guest
darkmatter4brains":2u2fk8g8 said:
ramparts":2u2fk8g8 said:
SpeedFreek":2u2fk8g8 said:
Cosmological time (and the age of the universe) is an approximation, based on a theoretical series of clocks in free-fall across time, under the least gravitational influence in their own epoch, co-moving with the expansion of the universe.

Beautifully put!

ah yes, and this reminded me how this is all related to the CMB!

When measured from Earth, the CMB (Cosmic Microwave Background) Radiation does look a tad warmer in one direction than it does in the other. This is because Earth is not perfectly comoving with the expansion of the Universe. It's in orbit around the Sun; The Sun "orbits" around in the Milky Way galaxy on one of the rings. And, the Milky way even has some overall motion towards the Hydra cluster.

The CMB exhibits the highest degree of homogeneity (and isotropy, really) in the frame that is comoving with the expansion of the Universe. Any measured change in this homogeneity would indicate that the frame from which you have measured it in, has some motion away from the expansion of the Universe.

The fact that the CMB is homogenous across the entire Universe, lets us be able to confidently define an age for the Universe that EVERYBODY, ANYWHERE can agree upon. Almost sounds "absolute" doesn't it!!

Actually, it almost sounds like the ether. But, not quite, thank goodness

Indeed - due to large-scale homogeneity and isotropy, we can talk about a CMB rest frame (in which the dipole you mentioned disappears). This is the closest we have to an "absolute" frame of reference in the universe - technically it's not actually privileged above any other reference frame, but we can treat it as such since it is unique in that the whole universe looks the same from it. </science>

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#### SpeedFreek

##### Guest
darkmatter4brains":1rpycoht said:
The fact that the CMB is homogenous across the entire Universe, lets us be able to confidently define an age for the Universe that EVERYBODY, ANYWHERE can agree upon. Almost sounds "absolute" doesn't it!!

If only we knew exactly what had happened between the Big-Bang and the recombination epoch, when the CMBR was released at what we currently estimate to be 380,000 years later, eh?

D

#### darkmatter4brains

##### Guest
SpeedFreek":17uszu7y said:
darkmatter4brains":17uszu7y said:
The fact that the CMB is homogenous across the entire Universe, lets us be able to confidently define an age for the Universe that EVERYBODY, ANYWHERE can agree upon. Almost sounds "absolute" doesn't it!!

If only we knew exactly what had happened between the Big-Bang and the recombination epoch, when the CMBR was released at what we currently estimate to be 380,000 years later, eh?

That's part of the reason I'm anxious for the LHC to finally turn on. If they find a Higg's particle, it will work towards confirming the Inflationary Big Bang Model too, since that uses a certain "type" of Higgs field. I think they're mainly looking for a different Higgs Particle/Field (the one for the SM, which fills in why particles have mass) with the LHC but, hey, if you find one, it makes the other a lot more plausible. That would get us back pretty darn far in time, provide a mechanism for (at least part of) an actual "bang", and help explain the shape and extent of the Universe quite a bit.

On the other hand, if they find out Higgs particles (and their associated fields) don't exist, well ...... :shock:

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#### FlatEarth

##### Guest
rpmath":1s8yxfnn said:
...The longer the path some one travels between 2 points of space-time, the shorter the time he measures.

But the earth loops around the sun, so there is a shorter path:
- Launch a rocket at 30 km/s (0.0001 c) in the opposite direction of earth translation to stop orbital speed.
- Keep it fixed relative to the sun compensating sun gravity with the rocket.
- Wait 1 year for earth returning to the same place.
One clock in the rocket will mark 1/sqrt(1-v/c) = 1.000000005 times what a clock in the earth marks
in 365.25 days of 24 hours of 3600 sec = 31557600 sec
the difference will be 0.000000005 * 31557600 = 0.157788 sec
it is small, less than 1/6 sec ...
but will be more than a clock on earth.
I think rpmath's post was lost in the flurry of posts. Does anyone care to comment?

SpeedFreek":1s8yxfnn said:
Excellent post!

Here is another calculator:

http://www.astro.ucla.edu/~wright/CosmoCalc.html
Thanks SpeedFreek. I appreciate it.

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#### SpeedFreek

##### Guest
...The longer the path some one travels between 2 points of space-time, the shorter the time he measures.

But the earth loops around the sun, so there is a shorter path:
- Launch a rocket at 30 km/s (0.0001 c) in the opposite direction of earth translation to stop orbital speed.
- Keep it fixed relative to the sun compensating sun gravity with the rocket.
- Wait 1 year for earth returning to the same place.
One clock in the rocket will mark 1/sqrt(1-v/c) = 1.000000005 times what a clock in the earth marks
in 365.25 days of 24 hours of 3600 sec = 31557600 sec
the difference will be 0.000000005 * 31557600 = 0.157788 sec
it is small, less than 1/6 sec ...
but will be more than a clock on earth.
I think rpmath's post was lost in the flurry of posts. Does anyone care to comment?
(my emphasis in bold)

To keep the rocket fixed, relative to the sun, compensating for the sun's gravity using the rocket, requires a constant acceleration for the whole year. Perhaps rpmath would like to do the math for this section too, and add it to his final total for the elapsed time on the rocket vs the elapsed time on the Earth?

If he does this he should find that the constant acceleration in order to fight against the suns gravity will cause a massive shift in simultaneity between the rocket and the Earth - the clock on the rocket will show less elapsed time at the end of the experiment as it has been constantly accelerating throughout the experiment.

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#### FlatEarth

##### Guest
SpeedFreek":33gbm9j9 said:
To keep the rocket fixed, relative to the sun, compensating for the sun's gravity using the rocket, requires a constant acceleration for the whole year. Perhaps rpmath would like to do the math for this section too, and add it to his final total for the elapsed time on the rocket vs the elapsed time on the Earth?

If he does this he should find that the constant acceleration in order to fight against the suns gravity will cause a massive shift in simultaneity between the rocket and the Earth - the clock on the rocket will show less elapsed time at the end of the experiment as it has been constantly accelerating throughout the experiment.
How would the deceleration of the rocket (leaving Earth to “park”) and the acceleration to land back on Earth influence time dilation?

J

#### Jerromy

##### Guest
I see an obvious debate started about the difference between relative velocity versus relative gravity. I am under the impression from what I know of Einstien's theories that time is distorted by velocity not gravity or acceleration (virtually identical).

Gravity being diverted into accretion or orbital velocity is far different from being held away from a gravitational pull. Flying in an airplane over the Earth is like our orbit of the sun. Being thrusted away from the sun's gravity is like standing on solid ground on Earth. There is always a trade-off in velocity versus acceleration. Fighting gravity is acceleration, PERIOD. Circumventing gravity is velocity, PERIOD. Find a balancing point between the milky way and andreomeda galaxies, send a probe to that location which sends clocks in various directions, and whichever clock records the shortest time relative to the others is going the slowest through space.

Seems alot more plausible than finding gravitons anyway.

H

#### harper05

##### Guest
It could accelerate in the opposite direction of earths orbit, then after a short period of time, slow down and stop.(I mean stop to the point on the orbital line where for 180 degrees, earth relative to the rocket would move away on the curve, then for the remainding 180, earth, relative to the rocket, would move back toward the rocket.) It would obviously then have to provide a small force to keep it at an earth orbit distance from the sun. But it would not then have to dec. or acc., it could simply be hit again by earth, on its way back around.

This would be an interesting way to test the speed of gravity. In that we would know exactly how much force, and time it would take to have an object in an exact fixed distance relative to the sun in its orbit of the galaxy. We could then deduce very accurately how fast the planets in a g-bound orbiting system interpret gravity?

Have we not done this already?

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#### FlatEarth

##### Guest
Jerromy":3c6787s4 said:
I see an obvious debate started about the difference between relative velocity versus relative gravity. I am under the impression from what I know of Einstien's theories that time is distorted by velocity not gravity or acceleration (virtually identical).

Gravity being diverted into accretion or orbital velocity is far different from being held away from a gravitational pull. Flying in an airplane over the Earth is like our orbit of the sun. Being thrusted away from the sun's gravity is like standing on solid ground on Earth. There is always a trade-off in velocity versus acceleration. Fighting gravity is acceleration, PERIOD. Circumventing gravity is velocity, PERIOD. Find a balancing point between the milky way and andreomeda galaxies, send a probe to that location which sends clocks in various directions, and whichever clock records the shortest time relative to the others is going the slowest through space.

Seems alot more plausible than finding gravitons anyway.
Hi Jerromy. I originally had the same view as you, but after looking the Wiki article, I realized I was wrong. I can't say I understand it, but I know I was wrong. :lol: Apparently without acceleration both observers in the "twins paradox" would see the other slow down and there would be no time dilation. Please see below and see some of the earlier posts on page 3 for a better explanation.
Kessy":3c6787s4 said:
For a more in depth discussion, I would recommend Wikipedia's article on the Twin Paradox.

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#### FlatEarth

##### Guest
harper05":390vw246 said:
It could accelerate in the opposite direction of earths orbit, then after a short period of time, slow down and stop.(I mean stop to the point on the orbital line where for 180 degrees, earth relative to the rocket would move away on the curve, then for the remainding 180, earth, relative to the rocket, would move back toward the rocket.) It would obviously then have to provide a small force to keep it at an earth orbit distance from the sun. But it would not then have to dec. or acc., it could simply be hit again by earth, on its way back around.
Hello, harper05. Unless I'm missing the point completely, my understanding is that acceleration is key to measuring time dilation, so to make a final measurement of time the rocket must return to Earth. By impacting Earth, it would accelerate back to Earth's orbital velocity which should produce the same result. I think.

H

#### harper05

##### Guest
I agree flat earth, the rocket has to acc. away from earth, then stop at one point in the orbital path. then acc away from the sun in its current orbital path,(around the galaxy). For earth it will acc. away from the rocket(on its orbital path), then acc. back into it, all the while acc. with the sun on its orbital path. Thus, the clock on the rocket would read the same as the clock on the earth.

If I had to word it, it would be as follows (hence I haven't done the math, but i've worded it) know what i mean :lol:

rocket acc away from earth 30km/s, earth acc away from rocket 30 km/s. they cancel.
rocket stops. earth acc 180 away and 180 toward. they cancell.
both acc with the sun on its orbit. they cancell.

My point is that we would know the exact force required, to compensate for the propagation of gravity. Because we would know the exact force and time required to keep that rocket at a fixed point relative to the sun. Hence the time should be different if gravity propagates at c. It should technically take 8 mn or so for the suns gravitational info to get to our rocket.

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#### harper05

##### Guest
We would have to take into consideration the gravitational time dialationl effect of earth of course. I mean calculate it in to the results.

S

#### SpeedFreek

##### Guest
harper05":2n8g5f1j said:
I agree flat earth, the rocket has to acc. away from earth, then stop at one point in the orbital path. then acc away from the sun in its current orbital path,(around the galaxy). For earth it will acc. away from the rocket(on its orbital path), then acc. back into it, all the while acc. with the sun on its orbital path. Thus, the clock on the rocket would read the same as the clock on the earth.

If the rocket accelerates away from the Earth in the opposite direction to Earth's orbital path, and then turns off its engines, it will free-fall into a retrograde orbit around the Sun. It does not have to accelerate to keep up with the Suns path around the galaxy. It will never escape the gravity of the Sun whilst it remains in free-fall, unless it accelerates away from the Sun at over 42 km/s (the escape velocity of the Sun, for an object at Earth's orbital distance).

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#### Couerl

##### Guest
Hi, this has been an interesting read for me.

One of the puzzles I have been contemplating lately regarding time and when it began relates to the moment when the initial inflationary period of the universe abated. Since the universe was expanding in all directions at once at greater than light velocity (at least very briefly) it seems to me that time could not decompress enough to be observable until that period of inflation had subsided. If, during inflation the universe did expand faster than light (see Guth, inflation theory) then one might assume that time was literally going backwards, in which case the universe would not have materialized or expanded at all. Since this is not the case and we are here and going "forward" through time, I can only surmise that time itself is dependant upon at least one of the 4 principal forces that seperated to form the laws of physics that we know and enjoy today. FWIW, I think it is a shame that we don't seem to have a better understanding of what time actually is than we did to begin with..

F

#### FlatEarth

##### Guest
Couerl":gz9jhb5f said:
Hi, this has been an interesting read for me.

One of the puzzles I have been contemplating lately regarding time and when it began relates to the moment when the initial inflationary period of the universe abated. Since the universe was expanding in all directions at once at greater than light velocity (at least very briefly) it seems to me that time could not decompress enough to be observable until that period of inflation had subsided. If, during inflation the universe did expand faster than light (see Guth, inflation theory) then one might assume that time was literally going backwards, in which case the universe would not have materialized or expanded at all. Since this is not the case and we are here and going "forward" through time, I can only surmise that time itself is dependant upon at least one of the 4 principal forces that seperated to form the laws of physics that we know and enjoy today. FWIW, I think it is a shame that we don't seem to have a better understanding of what time actually is than we did to begin with..
I don't think time ever moves in reverse. Theoretically, it stops in certain situations (like in black holes), but never reverses. Keep in mind that matter did not move at superluminal speeds. It was spacetime that expanded at that rate, and there is no speed limit on spacetime that we know of.

One explanation for the dramatic period of inflation was that gravity had yet to emerge, and when it did, it could only propagate at the speed of light, whereas the universe was expanding at a higher rate. That resolved itself when gravity, originating from everywhere, eventually came to dominate.

That's just off the top of my head without any references, so I may need to be corrected on the finer points.

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