Gravity vs Mass

[Valjean]

is that the same item Albert referred to as his greatest blunder?

LOL --No, I think that was his cosmological constant which, interestingly, later proved pretty accurate.
It is a good example of bad science, though, since it was added to make his theory fit a preconceived static universe. In good science facts follow from evidence, so it does qualify as a blunder.

General relativity - Wikipedia
Cosmological constant - Wikipedia

OK, I googled. It was his cosmological constant: Einstein's 'Biggest Blunder' Turns Out to Be Right | Space

 

[Valjean]

Time is an illusion

space is real enough
but the measure is all in your head

They're aspects of the same thing, both equally real -- and equally illusory.

 

[Polymath257]

is that the same item Albert referred to as his greatest blunder?

Nope. That was the cosmological constant. He introduced it to give a static universe since his original equations predicted either and expanding or a contracting universe. hence, when universal expansion was discovered, he said it was his greatest blunder.

Of course, much later, that cosmological constant was revived as 'dark energy' (although with a value quite different than Einstein's).

 

[Heyo]

is that the same item Albert referred to as his greatest blunder?

@exchemist :

Yes, it is. Or at least it is related. In his first formulation Einstein had a "cosmological constant" without which the universe could not have been static. His "blunder" was to assume that the universe was static. He could have predicted Big Bang cosmology years ahead of Friedmann, Lemaitre and Hubble.
The irony is that today the cosmological constant can be seen as a model for Dark Energy, so it wasn't a blunder after all.

 

[Polymath257]

I know roughly how spacetime is seen in GR. My question was if we can see it from an angle that gives @Terrywoodenpic 's statement some sense.
Assume the following analogy:
First we get rid of one spacial dimension so that we can imagine the universe in three dimensions like in the bed sheet analogy. Only this time it's a giant balloon. The direction of time is radial from the point of origin. The balloon "inflates" in the direction of time. There are dimples in the balloon where masses are. The distance of a point near a mass to the point of origin is different from points with no (or rather less) mass as well as the velocity those points travel outwards. Points with extreme masses in a small area make steep dimples and the surface doesn't expand at all. (Time stands still at the Schwarzschild radius of a black hole.) Also, fast moving objects make grooves.
There are some problems I see with this analogy: Space would necessarily have a positive curvature and it would decrease over time. Time would probably flow backwards within black holes. Negative mass would probably be impossible.
But in this model gravity would be a function of time as the outward movement (in the direction of time) would determine the gravity.
Now someone with a little more skill and a lot less lazy than me has to do the maths for that model. ;-)

This is actually an analogy I use myself. One good aspect is that there is a 'Big bang' at the origin and *nothing* 'before the Big Bang'.

OK, it seems that what you are wanting is a division of spacetime into 'spacelike' sections with a constant 'time coordinate' on each slice. Not only is this done, but it is how the equations for an expanding universe are derived.

There are a number of issues, though. The most basic is that there is more than one way to 'slice', which means different notions of the time coordinate for each method. The solution is to make sure that the 'time' in a slice measures 'proper time' from some fixed slice in the past (or, even better, a singularity which is common to all timelines). This works very well if you assume the universe is isotropic and homogeneous (same in all directions and at all points of a spacelike slice), but becomes more subtle when irregularities in energy distribution lead to non-uniform curvature and thereby a trickier definition of 'same time'. Again, this is done, but it is considerably more complicated mathematically.

In more generality, that past spacelink slice from which everything is measured also needs to have a 'timelike' vector (killing vector) at each point to make the problem well defined.

For more on all of this, I might suggest Weinberg's book on Cosmology, which goes into all of this in detail.

 

[exchemist]

@exchemist :

Yes, it is. Or at least it is related. In his first formulation Einstein had a "cosmological constant" without which the universe could not have been static. His "blunder" was to assume that the universe was static. He could have predicted Big Bang cosmology years ahead of Friedmann, Lemaitre and Hubble.
The irony is that today the cosmological constant can be seen as a model for Dark Energy, so it wasn't a blunder after all.

The cosmological constant is very far from being the same thing as General Relativity, surely?

It is only the application of GR to cosmology that raises the issue of a cosmological constant, so far as I understand it.

 

[Polymath257]

The cosmological constant is very far from being the same thing as General Relativity, surely?

It is only the application of GR to cosmology that raises the issue of a cosmological constant, so far as I understand it.

Some care is required because to large of a value for the CC would have observable effects on the dynamics of the solar system. And we know motions in the solar system to exquisite detail (which some seem to ignore).

 

[Valjean]

Some care is required because to large of a value for the CC would have observable effects on the dynamics of the solar system. And we know motions in the solar system to exquisite detail (which some seem to ignore).

Especially on New Years night, with people apparently trying to launch bullets into orbit.

 

[tas8831]

yep....sort of
a gov test rated me superior
when I was 13

Which government test was this?

but I have not let that go to my head

You sure about that? I seem to recall you proffering that at one point as a means of argument.

it's not important

so try not to worry over it

I don't worry at all, I just don't believe it given your history on this forum.

 

[Heyo]

This is actually an analogy I use myself. One good aspect is that there is a 'Big bang' at the origin and *nothing* 'before the Big Bang'.

OK, it seems that what you are wanting is a division of spacetime into 'spacelike' sections with a constant 'time coordinate' on each slice. Not only is this done, but it is how the equations for an expanding universe are derived.

There are a number of issues, though. The most basic is that there is more than one way to 'slice', which means different notions of the time coordinate for each method. The solution is to make sure that the 'time' in a slice measures 'proper time' from some fixed slice in the past (or, even better, a singularity which is common to all timelines). This works very well if you assume the universe is isotropic and homogeneous (same in all directions and at all points of a spacelike slice), but becomes more subtle when irregularities in energy distribution lead to non-uniform curvature and thereby a trickier definition of 'same time'. Again, this is done, but it is considerably more complicated mathematically.

I had a feeling that might be the case.

In more generality, that past spacelink slice from which everything is measured also needs to have a 'timelike' vector (killing vector) at each point to make the problem well defined.

For more on all of this, I might suggest Weinberg's book on Cosmology, which goes into all of this in detail.

Thanks for the recommendation. I found it online and will have a deeper look (although it might be slightly above my pay grade from a first look).

 

[We Never Know]

This is actually an analogy I use myself. One good aspect is that there is a 'Big bang' at the origin and *nothing* 'before the Big Bang'.

OK, it seems that what you are wanting is a division of spacetime into 'spacelike' sections with a constant 'time coordinate' on each slice. Not only is this done, but it is how the equations for an expanding universe are derived.

There are a number of issues, though. The most basic is that there is more than one way to 'slice', which means different notions of the time coordinate for each method. The solution is to make sure that the 'time' in a slice measures 'proper time' from some fixed slice in the past (or, even better, a singularity which is common to all timelines). This works very well if you assume the universe is isotropic and homogeneous (same in all directions and at all points of a spacelike slice), but becomes more subtle when irregularities in energy distribution lead to non-uniform curvature and thereby a trickier definition of 'same time'. Again, this is done, but it is considerably more complicated mathematically.

In more generality, that past spacelink slice from which everything is measured also needs to have a 'timelike' vector (killing vector) at each point to make the problem well defined.

For more on all of this, I might suggest Weinberg's book on Cosmology, which goes into all of this in detail.

What is the definition of *nothing* as you are using it here?

Here I'm going to define the "big bang" as change.

Did the change(the big bang) bring forth time or did time bring forth the change(the big bang)
(Or did they happened simultaneously)?

If at one point change completely ceases to happen, would time exist and could time be measured?

 

[Heyo]

What is the definition of *nothing* as you are using it here?

Here I'm going to define the "big bang" as change.

Did the change(the big bang) bring forth time or did time bring forth the change(the big bang)
(Or did they happened simultaneously)?

If at one point change completely ceases to happen, would time exist and could time be measured?

Where is north when you are standing at the North Pole?

 

[We Never Know]

Where is north when you are standing at the North Pole?

No where if you are standing exactly on the north pole.

 

[Subduction Zone]

you refer to dark energy?....dark matter?

any gravity there?

can't prove it ……..can you?

Why write posts that demonstrate absolute ignorance? Gravity is why astronomers know that Dark Matter exists.

 

[Heyo]

The cosmological constant is very far from being the same thing as General Relativity, surely?

It is only the application of GR to cosmology that raises the issue of a cosmological constant, so far as I understand it.

The cosmological constant is/was one part of the field equation for general relativity. Einstein dropped the Lambda later as it seemed to be zero and was not needed in an expanding universe.
So, yes, it is not the same thing, it is part of the same thing.

 

[Heyo]

No where if you are standing exactly on the north pole.

That is exactly how you have to imagine time in a Big Bang cosmology. A point where it makes no sense to ask "what was before?".

 

[We Never Know]

That is exactly how you have to imagine time in a Big Bang cosmology. A point where it makes no sense to ask "what was before?".

I didn't ask what was before.

Current models suggest at one point time nor the universe existed then after the big bang they both were in existance.

Did the change(the big bang) bring forth time or did time bring forth the change(the big bang)
(Or did they happen simultaneously)?

 

[Thief]

LOL --No, I think that was his cosmological constant which, interestingly, later proved pretty accurate.
It is a good example of bad science, though, since it was added to make his theory fit a preconceived static universe. In good science facts follow from evidence, so it does qualify as a blunder.

General relativity - Wikipedia
Cosmological constant - Wikipedia

OK, I googled. It was his cosmological constant: Einstein's 'Biggest Blunder' Turns Out to Be Right | Space

but no one seems to note.....
allow me to point it out


he used an illusion …..a man made measure
distance divided by another measure
increments of measure we call time

seconds don't exist......except in your head
miles are just increments we created for our feet

light doesn't care
neither do I

describing reality using an illusion....?

ooooops

 

[Thief]

Why write posts that demonstrate absolute ignorance? Gravity is why astronomers know that Dark Matter exists.

it cannot be proven

I know God exists......

 

[Subduction Zone]

it cannot be proven

I know God exists......

No, you only believe that God exists. And nothing is proven in the sciences. The sciences are respected because unlike religion it works, female dogs that have had puppies