# Time Dilation and Absolute Age of the Universe

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#### rpmath

##### Guest
Valado":1fxyhjzk said:
To get to an unique “absolute universe age” definition, valid along the total extent of our universe, it must be possible to be calculated, in the same way and getting the same result, from every point and time of the universe, that is, from Earth as well as from any very distant point In the universe (as well as from the most distant point in our universe), and as well as in the past (but, of course, resulting in a minor value). To do so, we must first define what absolute (and locally independent) observational point of view (APOV) should be used.

"getting the same result, from every point and time of the universe" is not possible... for every point at this time may be.
The problem is how to define "at this time"... well an APOV will work... such thing violates relativity, but relativity may be wrong saying that there are no preferred reference frames, and the APOV is one of those.

Valado":1fxyhjzk said:
The best definition for APOV I saw in here is the one ramparts mentioned as “we're talking about the time measured by an observer which following a standard free-fall path through the universe, so something which isn't travelling at significant speeds relative to the expansion of the universe and isn't under extreme gravitational forces”. To me… a very good try. This is almost to say: get a point in the intergalactic medium (no influence of gravitational forces) and motionless with respect to the rubber type fabric of space-time, which is expanding itself.

Suppose you can:
- measure the age of the universe at any point.
- know that point speed looking at the cosmic background radiation, and use it to get a time dilation to adjust that value.
- know the mass of the objects close and massive enough to produce a gravity time dilation, and use that to adjust your measure too.

The value you get is some sort of "space time interval" between you and the big bang.
With a law that you cannot move closer to the big bang, the light speed limit paradox disappears:

What looks as faster than light speed to an observer A can look as going to past for observer B, and the other way around, so, if you can go faster than light:
- go from A to B faster than light according to A.
- return from B to A faster than light according to B (going to past according to A)
- you are back to A before you leave, kill yourself before you leave, and end in a paradox.

If there is an APOV, you can go faster than light according to it without paradoxes.

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#### geofbrewer

##### Guest
Not a kooky idea at all. The problem is not necessarily solvable. The idea of a finite time or age for the universe has been discussed for millinia, even when we humans were unaware of the extent of the universe. We still aren't really sure of the extent of the universe. That said, it would be nice to put a number to the universes' birth aniversary. The question is what unit will we use? You and others suggest the atomic clock adjusted for a concept called a year. What is a year? Well it consists of so many vibrations of an isotope for a concept called a second. Need I go on?
Relativistically speaking, time is not a constant. So far Professor Einstein's ideas still hold. But that should not stop us from trying to figure out "how old is the universe"? Maybe some one will come up with a "gedankenexperiment" to rival Professor Einstein's. Just remember, his is not the only one out there in physics.

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#### Rado

##### Guest
All I can say is: you probably divided by zero somewhere, my friend.
Just kiddin', of course.

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#### FlatEarth

##### Guest
Here are a couple of things to ponder:

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.

2) Due to the expansion of space, we know that distant galaxies are moving away at greater than the speed of light. Assuming for a moment that Earth was at a place of zero movement, how would the superluminal velocity of those distant galaxies affect the passage of time there compared to Earth? An extreme idea would be that time actually would reverse, and given enough time (in this case time in reverse), those galaxies would un-form and dissolve. Perhaps this is the fate of the universe? :shock:

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#### harper05

##### Guest
Here is a cool quote from Dirac,
(from "The End of Time" by, Julian Barbour) as follows,

"On a beautiful oct. afternoon in 1963, I read an article about Paul Diracs attempt to unify einsteins gr with qt. A single sentence was to transform my life: "this result has led me to doubt how fundamental the four-dimensional requirement is in physics." In other words, Dirac was doubting the most wonderful creation of the 20th century physics, the fusion of space and time into space-time."

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#### Bill_Wright

##### Guest
Getting a working clock into a singularity, then getting information back out again might not be possible, certainly impossible with our current technology. However, since this is a thought experiment we can do everything we want to do. I would imagine that the clock might stop, just exactly as if it had reached the speed of light.

What might happen if the singularity evaporated? I see two possibilities:
1) the clock would have become energy and would then begin to dissipate (entropy: the big winner)
2) the clock would re-start at the exact same moment that it was inserted

Thoughts?

A

#### AcePilot101

##### Guest
I don't believe the universe has a beginning.
Sure, the current configuration began with the "big bang" some 15 billion (or less) years ago but scientists believe that a super-dense "singularity" exploded. How many times has this happened?
Perhaps, we could count the previous versions of the universe as blocks of time. For all we know, the universe could have been re-created billions of times!
Comments?

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#### SpeedFreek

##### Guest
FlatEarth":35n6bhuu 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.

Your usage of the term "absolute" speed is interesting. Absolute speed, relative to what? There is no absolute frame of reference, as, whatever your inertial frame of reference, the speed of light is always 300,000 km/s faster than yourself, and you can always consider yourself to be at rest in relation to the speed of light.

You are illustrating the "paradox" of the twins - who is to say who is in motion and who is at rest? Motion (and therefore speed) is not absolute, but is relative. The only invariant is that the speed of light is always 300,000 km/s relative to yourself, so your notions of space and time, relative to other frames of reference, must be dynamic.

This means that events that are simultaneous in one frame may not be simultaneous from another. The relativity of simultaneity tells us that different observers notions of "now" cannot be matched up in any absolute sense, when they are separated by space or time.

FlatEarth":35n6bhuu said:
2) Due to the expansion of space, we know that distant galaxies are moving away at greater than the speed of light. Assuming for a moment that Earth was at a place of zero movement, how would the superluminal velocity of those distant galaxies affect the passage of time there compared to Earth? An extreme idea would be that time actually would reverse, and given enough time (in this case time in reverse), those galaxies would un-form and dissolve. Perhaps this is the fate of the universe? :shock:

Time would only theoretically reverse for an object travelling faster than light, through space, relative to an object at rest. This is not the case with the distant galaxies. Here, space is expanding between those galaxies and ourselves, and just as we can consider ourselves to be at rest in our local frame, with light travelling 300,000 km/s faster than ourselves, so can the inhabitants of that distant galaxy consider the same thing in their local frame.

Those distant galaxies are not travelling through space faster than light, nor are they overtaking any photons which would violate causality.

With cosmological redshift, there is indeed cosmological time-dilation, but only at redshift=infinity would time be infinitely dilated. The upshot of this is that time does stop, relative to us, at redshift=infinity, but that redshift is only represented by the Big Bang itself!

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#### mabus

##### Guest
FlatEarth":29mptb8g said:
2) Due to the expansion of space, we know that distant galaxies are moving away at greater than the speed of light. Assuming for a moment that Earth was at a place of zero movement, how would the superluminal velocity of those distant galaxies affect the passage of time there compared to Earth? An extreme idea would be that time actually would reverse, and given enough time (in this case time in reverse), those galaxies would un-form and dissolve. Perhaps this is the fate of the universe? :shock:

My understanding is that the galaxies themselves are not moving at faster than the speed of light, but rather, that space itself is stretching between them (giving us the impression of superluminal velocity).

Bill_Wright":29mptb8g said:
Getting a working clock into a singularity, then getting information back out again might not be possible, certainly impossible with our current technology. However, since this is a thought experiment we can do everything we want to do. I would imagine that the clock might stop, just exactly as if it had reached the speed of light.

What might happen if the singularity evaporated? I see two possibilities:
1) the clock would have become energy and would then begin to dissipate (entropy: the big winner)
2) the clock would re-start at the exact same moment that it was inserted

Thoughts?

Some thought provoking questions.

I'm sure you and others are aware of the many notions out there that our universe itself may be a singularity, or the notions out there that singularities may contain universes within them. I suspect this is rather the direction you are heading towards here. I tend to agree with your suggestion that time would stop inside a singularity from the perspective of an outside observer.

I find it interesting that our universe was (is?) itself a singularity (from the perspective of an outside observer). The universe itself (as a singularity) would, as a dimensionless singularity experience singular time, that is to say, infinite time, infinite mass, infinite energy and so on. As it expands (from the perspective of someone inside the universe (singularity?) time seems to "break down" and localize so that all you can measure is local time and make generalized measurements of the whole.

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#### Kessy

##### Guest
I think the real point we need to take away from this is that our usual notions of time, including things like age, simultaneity, and even now, are all derived from our rather limited frame of reference here on Earth. When you start looking at things in a much different frame of reference, those concepts often need to be adjust, or even don't apply at all.

As an analogy, think of gravitational potential energy. In high school physics, we learned that it is equal to the object's mass multiplied by its height multiplied by the strength of gravity. This works fine for things on a human scale near the surface of the earth, but obviously, you need different ideas when you look at larger frames of reference. The strength of gravity is no longer constant, and the idea of "height" becomes a tad fuzzy.

One thing that is often forgotten about special relativity, is that it *is* relative, and works both ways. So, in the proverbial rocket ship, it's true that to an observer on Earth, time appears to be moving slower on the rocket then for the observer, but to an observer on the rocket, time also appears to be moving slower on Earth. The twin paradox really comes from time dilation caused by acceleration, which is the same for all observers.

So, when it comes to the age of the universe, it absolutely does depend on your frame of reference. But the thing to keep in mind is that relativity says there is no preferred inertial frame for physics, there *is* a preferred frame for people. From the Earth's point of view, the universe is about 13.7 billion years old. However, since most of the galaxies we can see have very small relative velocities to each other (at least in relativistic terms) after you account for the cosmic expansion of space time, that age will be about the same for most observers on planets in galaxies. And one would assume that's where you'd find most observers, at least ones we could talk to.

As for how the age of the universe from the perspective of a hypothetical observer outside of our space time, that's purely speculative. We don't even know if the notion of being outside space time even has meaning in the real world. And we certainly have no idea what rules would govern the interaction of such a thing with our universe.

So, to sum up, there's no such thing as an absolute frame of reference, or an absolute age of anything. When we talk about the age of the universe, we're talking about it from our point of view, and the point of view of any other observers that seem likely to be out there.

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#### SpeedFreek

##### Guest
Hi Kessy and welcome to the SDC (space dot com) forums!

That was an excellent first post indeed! I am looking forward to hearing more from you.

One small point to note though - the 13.7 billion year age for the universe is not really taken from Earth's point of view, it is taken from the point of view of a theoretical clock out in deep space, away from as much gravitational influence as is possible. The difference, however, is negligible.

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#### drwayne

##### Guest
Welcome indeed Kessy.

Wayne

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#### Jerromy

##### Guest
ramparts":3iho2aln said:
Spacetime is not made of rubber.

Perhaps not, but rubber could be made of spacetime with the expansion properties linked inward for recoil. :lol:

AcePilot101":3iho2aln said:
I don't believe the universe has a beginning.
Sure, the current configuration began with the "big bang" some 15 billion (or less) years ago but scientists believe that a super-dense "singularity" exploded. How many times has this happened?
Perhaps, we could count the previous versions of the universe as blocks of time. For all we know, the universe could have been re-created billions of times!
Comments?

Or perhaps an infinite amount of times, and therein lies the basis of faith. God's clock ticks light years while ours ticks seconds.

Bill_Wright":3iho2aln said:
What might happen if the singularity evaporated? I see two possibilities:
1) the clock would have become energy and would then begin to dissipate (entropy: the big winner)
2) the clock would re-start at the exact same moment that it was inserted

Thoughts?

In your anything is possible hypothetical existence, you could just make the clock indestructable and therefore time would continue from the moment it was inserted. If it is a hydrogen clock that is inserted into said singularity, I'm curious if the hydrogen atoms of which it counts electronic revolutions, would be able to reform in the entropy during said evaporation. If the original hydrogen atoms which were inserted in with the omnipotent registering device had a delay in recoalescence after evaporation it might throw off your percieved timing.

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#### ramparts

##### Guest
Bill_Wright":1vcb84oz said:
Getting a working clock into a singularity, then getting information back out again might not be possible, certainly impossible with our current technology. However, since this is a thought experiment we can do everything we want to do. I would imagine that the clock might stop, just exactly as if it had reached the speed of light.

What might happen if the singularity evaporated? I see two possibilities:
1) the clock would have become energy and would then begin to dissipate (entropy: the big winner)
2) the clock would re-start at the exact same moment that it was inserted

Thoughts?

Hi Bill. You have yet to successfully explain what "inside a singularity" means. It's like saying "inside a point particle." It makes no sense.

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#### FlatEarth

##### Guest
SpeedFreek":3esjjq3i said:
FlatEarth":3esjjq3i said:
2) Due to the expansion of space, we know that distant galaxies are moving away at greater than the speed of light. Assuming for a moment that Earth was at a place of zero movement, how would the superluminal velocity of those distant galaxies affect the passage of time there compared to Earth? An extreme idea would be that time actually would reverse, and given enough time (in this case time in reverse), those galaxies would un-form and dissolve. Perhaps this is the fate of the universe?
Time would only theoretically reverse for an object travelling faster than light, through space, relative to an object at rest. This is not the case with the distant galaxies. Here, space is expanding between those galaxies and ourselves, and just as we can consider ourselves to be at rest in our local frame, with light travelling 300,000 km/s faster than ourselves, so can the inhabitants of that distant galaxy consider the same thing in their local frame.

Those distant galaxies are not travelling through space faster than light, nor are they overtaking any photons which would violate causality.

With cosmological redshift, there is indeed cosmological time-dilation, but only at redshift=infinity would time be infinitely dilated. The upshot of this is that time does stop, relative to us, at redshift=infinity, but that redshift is only represented by the Big Bang itself!

mabus":3esjjq3i said:
My understanding is that the galaxies themselves are not moving at faster than the speed of light, but rather, that space itself is stretching between them (giving us the impression of superluminal velocity).
Of course you are both right. Receding galaxies are not actually moving through space, so there is no impact on time in this case. I thought in the context of the discussion here, it was something worth touching upon.

SpeedFreek":3esjjq3i said:
FlatEarth":3esjjq3i 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.

Your usage of the term "absolute" speed is interesting. Absolute speed, relative to what? There is no absolute frame of reference, as, whatever your inertial frame of reference, the speed of light is always 300,000 km/s faster than yourself, and you can always consider yourself to be at rest in relation to the speed of light.

You are illustrating the "paradox" of the twins - who is to say who is in motion and who is at rest? Motion (and therefore speed) is not absolute, but is relative. The only invariant is that the speed of light is always 300,000 km/s relative to yourself, so your notions of space and time, relative to other frames of reference, must be dynamic.

This means that events that are simultaneous in one frame may not be simultaneous from another. The relativity of simultaneity tells us that different observers notions of "now" cannot be matched up in any absolute sense, when they are separated by space or time.
Yes light speed is invariant, and time varies according to the speed of the observer. An observer travelling at half light speed who shoots a laser beam straight ahead will measure that beam moving at the speed of light relative to him because time passes more slowly for him at the speed he is travelling. Speed is absolute, with the slowest rate being zero and the fastest being light speed. Time is not. The way to determine absolute zero speed is by measuring how time passes under different circumstances.

So who is in motion? The people on Earth move as the planet rotates, orbits the sun, moves with the solar system as it orbits the galactic center, and moves with the galaxy as it approaches Andromeda. A spaceship could travel opposite the direction of the solar system as it moves in the Milky Way, and ultimately move more slowly. We have measured time dilation in limited ways (planes in flight and orbiting satellites) and have proven that time does slow down in those cases. I'd like to see an experiment to see if we can find a circumstance that produces the opposite result.

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#### SpeedFreek

##### Guest
FlatEarth":63u1lev3 said:
A spaceship could travel opposite the direction of the solar system as it moves in the Milky Way, and ultimately move more slowly.

Relative to what?

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#### FlatEarth

##### Guest
SpeedFreek":1artaciw said:
FlatEarth":1artaciw said:
A spaceship could travel opposite the direction of the solar system as it moves in the Milky Way, and ultimately move more slowly.

Relative to what?
Than the Earth. My point is everything has an absolute speed between zero and C.

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#### SpeedFreek

##### Guest
FlatEarth":32ld6xqs said:
SpeedFreek":32ld6xqs said:
FlatEarth":32ld6xqs said:
A spaceship could travel opposite the direction of the solar system as it moves in the Milky Way, and ultimately move more slowly.

Relative to what?
Than the Earth. My point is everything has an absolute speed between zero and C.

And my point is that you are saying the spaceship is moving slower than the Earth. I am asking in what frame of reference is the spaceship moving slower than the Earth? The spaceship is moving slower than the Earth, relative to what?

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#### Kessy

##### Guest
FlatEarth":392rvq4r said:
Yes light speed is invariant, and time varies according to the speed of the observer. An observer travelling at half light speed who shoots a laser beam straight ahead will measure that beam moving at the speed of light relative to him because time passes more slowly for him at the speed he is travelling. Speed is absolute, with the slowest rate being zero and the fastest being light speed. Time is not. The way to determine absolute zero speed is by measuring how time passes under different circumstances.

I'm sorry, FlatEarth, but I'm afraid you've slightly misunderstood time dilation here. Time doesn't change when you move at relativistic speeds, it simply looks different. Imagine you're looking at a cube without depth perception. If you look at it straight at one of the faces, it looks like a square. But if you move so you're looking straight at one of the corners, it looks like a hexagon. The cube hasn't changed, it just looks different and measures differently because your frame of reference changes.

If you take your observer moving at 0.5c and another stationary observer, both observers will experience time passing normally for them. If either observer shoots a laser in any direction, both observers will measure that laser as moving at c relative to them. So if the ship shoots the laser in the direction it's moving, both see it moving the same speed relative to them. If the stationary observer shoots a laser in the direction opposite to the direction the ship is moving, both will again observe that laser moving at c relative to them. And so on in every possible combination. This happens because each observer sees the other as time dilated. The observer on the planet sees time moving on the ship moving slowly, and the ship sees time moving on the planet equally slowly. Time doesn't change between the frames of reference, it just looks different.

So, yes, c is invariant, and time is not. But speed is not absolute. It doesn't matter how fast you're going, time will always appear to be the same to you, and you'll see the same distortions in things moving fast relative to you. The fact is that there is *no* experiment you can perform that will determine your absolute speed. Physics and the universe look exactly the same no matter how fast you're going, so long as you're moving at a constant speed in a constant direction.

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#### FlatEarth

##### Guest
SpeedFreek":25tudg0e said:
And my point is that you are saying the spaceship is moving slower than the Earth. I am asking in what frame of reference is the spaceship moving slower than the Earth? The spaceship is moving slower than the Earth, relative to what?
In absolute terms, it doesn't matter what frame of reference is used. On Earth, the astronauts would appear to age more slowly. On the spaceship, the astronauts would see those on Earth age more quickly. At a third location, aliens who have found a zero movement location would see the astronauts aging more slowly than those on Earth, but the people on Earth and the astronauts would age more quickly than the aliens.

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#### SpeedFreek

##### Guest
There are no absolute terms, only relative comparisons.

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#### FlatEarth

##### Guest
Kessy":15e24cuo said:
I'm sorry, FlatEarth, but I'm afraid you've slightly misunderstood time dilation here. Time doesn't change when you move at relativistic speeds, it simply looks different. Imagine you're looking at a cube without depth perception. If you look at it straight at one of the faces, it looks like a square. But if you move so you're looking straight at one of the corners, it looks like a hexagon. The cube hasn't changed, it just looks different and measures differently because your frame of reference changes.

If you take your observer moving at 0.5c and another stationary observer, both observers will experience time passing normally for them. If either observer shoots a laser in any direction, both observers will measure that laser as moving at c relative to them. So if the ship shoots the laser in the direction it's moving, both see it moving the same speed relative to them. If the stationary observer shoots a laser in the direction opposite to the direction the ship is moving, both will again observe that laser moving at c relative to them. And so on in every possible combination. This happens because each observer sees the other as time dilated. The observer on the planet sees time moving on the ship moving slowly, and the ship sees time moving on the planet equally slowly. Time doesn't change between the frames of reference, it just looks different.

So, yes, c is invariant, and time is not. But speed is not absolute. It doesn't matter how fast you're going, time will always appear to be the same to you, and you'll see the same distortions in things moving fast relative to you. The fact is that there is *no* experiment you can perform that will determine your absolute speed. Physics and the universe look exactly the same no matter how fast you're going, so long as you're moving at a constant speed in a constant direction.
I agree with some of the examples you have cited, but not the one about the movement of time on the planet vs. the spaceship. For example, we have measured that time did slow down for an astronaut orbiting Earth. It didn't slow down for the person in space and those on Earth, did it? That's because the astronaut was moving faster than the clock on Earth. If it were strictly a matter of relative movement, time dilation would not have been measured on the watch of the astronaut.

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#### Kessy

##### Guest
FlatEarth":31oq5wu1 said:
I agree with some of the examples you have cited, but not the one about the movement of time on the planet vs. the spaceship. For example, we have measured that time did slow down for an astronaut orbiting Earth. It didn't slow down for the person in space and those on Earth, did it? That's because the astronaut was moving faster than the clock on Earth. If it were strictly a matter of relative movement, time dilation would not have been measured on the watch of the astronaut.

Flat, the difference between the astronaut's watch and the ground clock that is observed once the astronaut has returned to the ground is caused by the time dilation that occurs while the astronaut is accelerating to get into space and then back to Earth. Acceleration is absolute and can be easily measured without an outside frame of reference, therefore the time dilation it causes is also absolute. While the astronaut is in flight, if he used a two way video link to communicate with Earth, he will observe time on earth appearing to go slow, and the earth will also observe time going slowly on the ship.

I know it's a bit hard to wrap your head around. Think of it like light being distorted when it goes through water. Standing on the ground, things under the water look distorted, but for a diver in the water, things on the land also look distorted.

For a more in depth discussion, I would recommend Wikipedia's article on the Twin Paradox.

M

#### mabus

##### Guest
FlatEarth":171mbbkz said:
At a third location, aliens who have found a zero movement location would see the astronauts aging more slowly than those on Earth, but the people on Earth and the astronauts would age more quickly than the aliens.

This is sort of the problem. As with my atomic clock experiment in the above demonstrates, there is no such location. All measurements inside the universe are nessecarily localized measurements. Every bit of space-time is stretching and to some extent more or less, subject to gravitational forces. Every bit of space is falling through space, there is no single place in all the universe that is free of this effect. There is no single place in the universe which you can use as an absolute reference frame, they are all relative to something else which is equally valid (and equally non-absolute)

O

#### orbit_er

##### Guest
The idea that the Universe "began" at some point is a frivilous, silly idea, and the argument constructed from it is hopelessly flawed. Creationists dismiss counter arguments without analysis, so I feel justified in doing the same.

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