Does General relativity really agree with reality?

[TJ McCaustland]

Hello everyone, TJ here after a long vacation of study and speculation. I came here to ask a simple yet deceivingly complex question, Does general relativity Really agree with reality? Well before everybody picks sides or starts stating that Einstein was a brilliant man far above my level in learning which he was, I will present a few of my findings here.

 

1. In reality mass does affect the universe, but why then should mass effect the "fabric" of space when the universe is actually a dimensionless multiverse? Is that just our way of thinking of it or is the theory flawed at some specific point or is the entire universe actually limited?

 

2. In equation he accounts for the cosmological principal, but does he really account for the seemingly limitless, dimensionless multverse we live in? or does he forget that.

 

I ask that here you keep the discussion in a professional calm manner and not start a flame war, and that you please do not criticize these questions unless they are completely wrong and if so show me where to correct them, after all science started with the question "why?"

[Bignose]

Does general relativity Really agree with reality?

Here's a pretty relevant paper "The Confrontation between General Relativity and Experiment"

 

113 pages of just how closely the predictions from GR agree with what is measured. http://arxiv.org/abs/1403.7377

 

after all science started with the question "why?"

Science and philosophy are certainly intertwined and interrelated. However, "why" is typically not a scientific question. Science is typically more about making predictions that agree with measurement. "Why?" is much more philosophy.

Edited January 19, 2015 by Bignose

[TJ McCaustland]

What the article states is quite true how GR agrees with reality, but I saw another topic in specs that asked the same question in a much more convoluted way, it's just that I had a question and you answered it, so thanks.

[Phi for All]

please do not criticize these questions unless they are completely wrong

Well, that's not going to happen. You're going to get criticism on all the wrong parts, whether completely or partially wrong. Isn't that what you really want by coming here, knowing it's going to be tough, knowing that if you can convince this crowd, you must be on to something?

 

after all science started with the question "why?"

Philosophers started with "why?", and found it to be lacking. That's when they came up with science.

[Strange]

1. In reality mass does affect the universe, but why then should mass effect the "fabric" of space when the universe is actually a dimensionless multiverse?

 

What evidence is there that the universe is a dimensionless multiverse? And what does "dimensionless" mean?

 

but does he really account for the seemingly limitless, dimensionless multverse we live in? or does he forget that.

 

Maybe he didn't know it. After all, there seems to be little evidence for it.

[Phi for All]

What evidence is there that the universe is a dimensionless multiverse? And what does "dimensionless" mean?

I can't believe I missed that. Is this just another misunderstood word, like "logic" and "theory"?

[TJ McCaustland]

Dimensionless meaning without a set number of dimensions

[andrewcellini]

Dimensionless meaning without a set number of dimensions

what do you mean by dimensions then? it seems you may be using this term in an unconventional way.

[Strange]

Dimensionless meaning without a set number of dimensions

 

The universe appears to have 4 dimensions, so I don't know where you get that idea.

[Robittybob1]

 

The universe appears to have 4 dimensions, so I don't know where you get that idea.

I've heard it has more dimensions than just 4. 11 is a number often quoted.

[Mordred]

The term dimensions, can represent various aspects in differential geometry. There is Three spacial dimensions, one time dimension, you can also assign a dimension to specific interactions such as charge, color,flavor, etc.

 

The 11 dimensions you mentioned is string theory.

[Bignose]

I've heard it has more dimensions than just 4. 11 is a number often quoted.

There are flavors of string theory proposed that appear to use 11 dimensions. But, none of these are really confirmed as string theory itself isn't really confirmed.

 

We have to be very careful about talking about counts of dimensions, because I am not sure that the count really means anything.

 

For example, if I look at a single particle (particle here is a very generic term, not a 'particle' as in particle physics, but more a lump of something we are looking at) as it moves in time, I have 1 dimension time, t. And it moves in space, so now I have 3 space dimensions, x, y, z. But, as it is moving, I also have a velocity, v_x, v_y, v_z. Velocity is independent of position (i.e. the particle could have the entire range of speeds no matter what its position), so each of those 3 are dimensions, too, simply because they are independent of the other dimensions we have defined. In the same way, if those velocities change, we have accelerations, a_x, a_y, a_z. So now we're up to 10 dimensions. Just on a single particle.

 

There is almost no limit to this game. 1) we can keep talking about changes in the derivatives of position... e.g. changes in accelerations are jerks, changes in jerks are jounces, etc. 2) we can start adding more than 1 particle... a 2nd particle would double the number of dimensions less 1 (time). That is, a 2nd particle would have a position, velocity, acceleration, and so on. 3) The above assumes each particle is identical, we can start talking about different particles and introduce more dimensions that way, such as with measures of the particle size (like volume, or diameter), particle shape (sphericity, roughness, etc.), make up (density, chemical composition, etc.). A particle could even have its own time, such as an age if our particle was a cell, or how much a chemical reaction has occurred. There are even infinite dimension dimensions such as a chemical composition profile in the particle where function spaces need to be used.

 

In short, there can be a heck of a lot of dimensions, even in some very simple systems.

 

I think how many dimensions a mathematical description uses doesn't mean nearly as much as how accurate that mathematical description is. So, I wouldn't get hung up on how many dimensions a certain flavor of string theory has. I am not aware there are any physical evidence of the 'curled up' dimensions used by these theories, anyway. If someone has an example, it would be appreciated if it were posted.

[Sensei]

For example, if I look at a single particle (particle here is a very generic term, not a 'particle' as in particle physics, but more a lump of something we are looking at) as it moves in time, I have 1 dimension time, t. And it moves in space, so now I have 3 space dimensions, x, y, z. But, as it is moving, I also have a velocity, v_x, v_y, v_z. Velocity is independent of position (i.e. the particle could have the entire range of speeds no matter what its position), so each of those 3 are dimensions, too, simply because they are independent of the other dimensions we have defined. In the same way, if those velocities change, we have accelerations, a_x, a_y, a_z. So now we're up to 10 dimensions. Just on a single particle.

 

I am kinda surprised that you're calling velocity and acceleration "dimensions".

 

This way, you can call charge of charged particle yet another dimension.. And polarization another 3?

 

Imagine simple math linear equation:

f(x) = ax+b

at

x=0 f(0)=b

x=1 f(1)=a+b

x=2 f(2)=2a+b

and so on with increasing x

 

In this simple case x and y are dimensions, but a and b are not.

X is like time, and a and b are parameters. They're not dimensions by them self.

f(x) is predicting future "position" at different time x.

 

Extend this to 3 spatial dimensions, and 1 time:

 

x,y,z - position

 

// increase of position by velocity vector every second (or fraction of second)

x += vx;

y += vy;

z += vz;

 

vx,vy,vz - velocity vector in m/s

(it's kinda like a and b params in 1st example equation but extended to multi-dimensions)

 

Then make vx,vy,vz variable in time:

 

// increase of velocity by acceleration vector every second (or fraction of second)

vx += ax;

vy += ay;

vz += az;

 

ax,ay,az - acceleration vector

 

vx,vy,vz, ax, ay, az are kinda like hidden variables. They're part of object. But not dimensions on their own.

 

This is at least how it's implemented in the all modern 3d games. If something acts on 3D object, we change ax,ay,az of object, and this changes vx,vy,vz (in future), and this changes real positions (in future) (f.e. 60 frames per second: x+=vx/60.0;y+=vy/60.0;z+=vz/60.0;).. In the mean time there is performed collision detection to make sure objects don't overlap.

Example: projectile fired by player will have x=player.x,y=player.y,z=player.z,vx=vy=vz=0, and ax,ay,az set to some high initial value in direction of shooting.

Then by animating (decreasing) ax,ay,az in time, projectile position x,y,z will be dragged to the ground.

[ajb]

I am kinda surprised that you're calling velocity and acceleration "dimensions".

Maybe better to call them degrees of freedom in classical mechanics, or 'geometric directions'. The dimensions of a manifold are the number of local coordinates that you need. In local coordinates can think of velocity as the fibre coordinate of the tangent bundle of your position space. The acceleration is then the 'second order' coordinate on the second order tangent bundle of the position space and and so on.

 

Any curve on your position space, that is a trajectory of a particle, can be lifted canonical to any higher order tangent bundle, which we can interpret at a given time as specifying a particle's position, velocity, acceleration and so on.

 

Imagine simple math linear equation:

f(x) = ax+b

at

x=0 f(0)=b

x=1 f(1)=a+b

x=2 f(2)=2a+b

and so on with increasing x

 

In this simple case x and y are dimensions, but a and b are not.

X is like time, and a and b are parameters. They're not dimensions by them self.

f(x) is predicting future "position" at different time x.

Again, we have poor choice of nomenclature; x and y are coordinates. They allow you to define the 'geometric directions'.

[StringJunky]

Is it ok to think of dimensions as 'measurable parameters relating to space'?

Edited January 30, 2015 by StringJunky

[ajb]

There is the mathematical notion of dimension, which here is the smallest number of coordinates you need on your manifold or vector space to describe each point. There is also the notion of fundamental dimensions or units, like mass, length and time. The notion you suggest seems closer to the fundamental dimensions, especially where length and time are involved.

[StringJunky]

There is the mathematical notion of dimension, which here is the smallest number of coordinates you need on your manifold or vector space to describe each point. There is also the notion of fundamental dimensions or units, like mass, length and time. The notion you suggest seems closer to the fundamental dimensions, especially where length and time are involved.

Yes, the mathematical version is over my head at the moment.

[Bignose]

There is the mathematical notion of dimension, which here is the smallest number of coordinates you need on your manifold or vector space to describe each point. There is also the notion of fundamental dimensions or units, like mass, length and time. The notion you suggest seems closer to the fundamental dimensions, especially where length and time are involved.

This. This was better written than what I could express, and exactly what I mean with my example above.

[KenBrace]

 

The universe appears to have 4 dimensions, so I don't know where you get that idea.

 

According to modern string theory there are 11 dimensions.

[Strange]

 

According to modern string theory there are 11 dimensions.

 

http://www.boctaoe.com/

 

There are known to be 4 dimensions. There may be more according to some theories. That doesn't change the fact that the universe is not "dimensionless".

[Sensei]

 

According to modern string theory there are 11 dimensions.

 

String theory is not confirmed.

 

Confirmed theories are basing in experimental physics.

[imatfaal]

 

String theory is not confirmed.

 

Confirmed theories are basing in experimental physics.

 

 

Exactly - string theories not only lack any experimental proof; many of them cannot propose any experiments that are even remotely feasible in the near future that might provide that proof.