Lorentz Transformations (split from why nothing >c)

[Janus]

Has there been observational verification that this expansion/recession has the same properties when viewed from whatever point in the universe?

 

We only have the Solar system to make direct measurements but it seems to be accepted that "everywhere is the centre". Is that down to experimental observation? Or is it a theory that stands up so far?

Well, the only other alternative is to assume that the solar system is "special" and uniquely located at the center of the expansion.

And we have been burned by that assumption too many times:

First the Mediterranean sea was the at the center of the world.

Then the Earth was at least at the center of the solar system.

Then when that turned out not to be so it appeared that the solar system was at the center of the galaxy (which at the time was thought to be the entirety of the universe), again t find out that not only were we in the outskirts, but our galaxy was just one of many.

Let's just say that we have become leery of any observation that points to our having any type of special position in the universe.

[geordief]

Well, the only other alternative is to assume that the solar system is "special" and uniquely located at the center of the expansion.

And we have been burned by that assumption too many times:

First the Mediterranean sea was the at the center of the world.

Then the Earth was at least at the center of the solar system.

Then when that turned out not to be so it appeared that the solar system was at the center of the galaxy (which at the time was thought to be the entirety of the universe), again t find out that not only were we in the outskirts, but our galaxy was just one of many.

Let's just say that we have become leery of any observation that points to our having any type of special position in the universe.

Yes i see that (forgot that I knew it since it is so second nature now) . But ,if we we view the Universe as it has developed since the time around the BB are there parts of it that are "closer" to that "region" than others? Are there parts that are "further away "?

 

I can see that spacially that makes no sense to ask but can it be asked in terms of spacetime?

 

Are there any parts of the Universe that are in any sense "closer" to the centre of the Universe (the "BB" ) than others?

 

Could there be any objects that are "trapped" in the Big Bang event in a similar way to how they could be in a Black Hole and so ,in a sense are "forever young"?

 

 

This is a consequence of the model of expansion. The model is consistent with all the evidence we have.

 

But, actually, if you were to draw a pattern of dots with one at the centre and then animate it so that every dot moved away from the centre at a speed that was proportional to its distance from the centre, then you would find that all dots moved away from one another in the same way. So you choose any other dot as the centre and nothing would change. (You could test this with a small number of dots and drawings, if it isn't immediately obvious why.)

Does that imply that an asymettrical global expansion is impossible ?

Edited April 26, 2017 by geordief

[Strange]

Does that imply that an asymettrical global expansion is impossible ?

 

 

I don't think so. But I think the asymmetry would be visible from (nearly?) everywhere.

[geordief]

 

 

I don't think so. But I think the asymmetry would be visible from (nearly?) everywhere.

So is that what they are talking about when they say the Cosmic Microwave Background is almost completely homogeneous?

 

There are tiny asymmetries but as a pattern it is symmetric?

[pzkpfw]

...

Are there any parts of the Universe that are in any sense "closer" to the centre of the Universe (the "BB" ) than others?

...

If your left eyeball is taken as the centre, then your right eyeball is closer to the centre than either of my eyeballs.

 

If Alpha Centauri A is taken as the centre, then Proxima Centauri is closer to the centre than Aldebaran.

[geordief]

If your left eyeball is taken as the centre, then your right eyeball is closer to the centre than either of my eyeballs.

 

If Alpha Centauri A is taken as the centre, then Proxima Centauri is closer to the centre than Aldebaran.

But if the Universe is a set of events (in the spacetime sense , I suppose) is any event more central in any meaningful way than any other? Events "nearer" the BB?

[imatfaal]

But if the Universe is a set of events (in the spacetime sense , I suppose) is any event more central in any meaningful way than any other? Events "nearer" the BB?

The Big Bang happened everywhere. Remember everything is flying away from everything else - rather than everything flying away from a central explosion

 

I realise the "flying" bit is wrong - but ignore that bit - the important part is the fact that the big bang was/is a process which happened/is happening everywhere and that there was no core which expanded outwards just that everything moved away (fairly swiftly) from its neighbours

[Strange]

So is that what they are talking about when they say the Cosmic Microwave Background is almost completely homogeneous?

 

 

Isotropic is probably the more important aspect, in this case.

[pzkpfw]

But if the Universe is a set of events (in the spacetime sense , I suppose) is any event more central in any meaningful way than any other? Events "nearer" the BB?

There certainly were times when certain things * occurred (or started, or stopped) when everything was closer together than it is now. That's a kind of "nearer".

 

But be sure that doesn't mean nearer a central location; everything was closer to everything else (i.e. I am not contradicting imatfaal).

 

 

(* e.g. inflationary period)

Edited April 26, 2017 by pzkpfw

[robinpike]

Because the escalator example was used to illustrate the principle of local speed limits vs separation rate. It's not a good analogy for every aspect of expansion.

 

In this case, the critical point is that space is expanding per unit of distance. So, to put it in manageable terms: After X amount of time, every mile gains an inch.

 

Someone who is one mile away will then recede at a rate of 1 inch per X. Someone two miles away at 2 inches per X. Three miles at 3 inches per X. And so on.

 

The farther away you get from something, the faster you will move away from it. There is more space between you to expand, and so you get a larger amount of distance between you being added due to expansion in the same amount of time.

 

Eventually you get so far away that, as explained above, the distance is increasing faster than the light is traversing that distance. Like a train with track being laid in front of it faster than the train is moving, it will never be able to reach the end of the line.

 

Thanks, that explains how light may not be able to reach every part of the universe. Is it the case that we are happy with how the accelerating distance between galaxies occurs? Or are there issues?

 

For example, if the increase in distance between galaxies is due to 'dark energy' pushing the galaxies apart, wouldn't objects generally moving through this dark energy feel a drag - and slow down? Or is 'dark energy' like photons, in that regardless of your own speed and direction, 'dark energy' moves at the same constant speed to you, regardless of the speed and direction of your own reference frame. But even then, wouldn't a Doppler shift in the amount of energy of the 'dark energy' still occur for some speeds / directions?

 

Or perhaps is it that space has 'substance' - and it is space itself that is increasing between the galaxies - and dragging the galaxies with itself? But then wouldn't the same problem occur for objects generally moving through space, in that they would experience a 'drag' from the space, and slow down?

 

Just wondering if these are valid issues or not?

Edited April 27, 2017 by robinpike

[Strange]

Space is not a substance, just the distance between objects. It turns out that in a universe described by the equations of general relativity (as ours appears to be) that objects will tend to get further apart (*) over time if no force acts on them (and if there is an even distribution of matter). This is slightly counterintuitive, as we tend to a some that things will just stay "where they are". But this is the reason for expansion.

 

Locally, things are held together by gravity and other forces, and so the expansion only occurs over very large scales, where these forces become insignificant.

 

There is no "drag" from space. But it was generally assumed that gravity would gradually slow the expansion and start a process of collapse. But then it was found that the expansion is accelerating. This acceleration is attributed to "dark energy" - something unknown, but that can be modelled as an extra energy throughout the universe.

 

(*) Or get closer together. Depending on energy density, initial conditions, etc.

Edited April 27, 2017 by Strange

[David Levy]

Have you ever been on one of those moving walkways that are basically like flat escalators that they have in some places, especially airports?

 

So let's imagine a top running speed of 30 mph. Absolutely no one can get any faster than that no matter how hard they try to run. Now let's imagine you try sprinting down one of those moving walkways.

 

You still can't run any faster, but as the walkway carries you along with it, you could certainly recede from someone standing at one end of the walkway faster than your top running speed wild take you. The speed at which you can run around on that walkway still has the same limit it always has had. You may now move away from someone at one end of the walkway at 45 mph, but you still can't run at 45 mph. You're still capped at your normal sprinting rate compared to someone riding along next to you.

 

Similarly, the speed at which anything can move through local space is still capped at c. However, the region of Spaxe you are moving through is growing more distance from the region of space on the opposite end of the universe because of the metric expansion of space. As they become more distance, the space may "carry you along" so that you recede from the other end of the universe faster than the speed of light.

 

You still can't move any faster than normal through space, but the space you are moving through is not restricted to the same speed limit, so to speak.

 

Now we understand the difference between "Moving away" and "receding".

 

Hence, the far end galaxy is receding from us at a speed which is greater than the speed of light.

However, as we discuss on relativity - it is clear that the outcome is that the relative speed between us and this galaxy is faster than the speed of light.

So, why this semantic is so important for our scientists?

 

If I understand it correctly:

 

Based on the current hypothesis - nothing can move faster than a speed of light.

So in order to bypass that "nothing can move faster" we call it receding.

Hence, we can keep with our hypothesis that nothing can move faster than the speed of light while we justify the simple evidence that there are galaxies which are moving away from us at a speed which is greater than the speed of light.

By now, I assume that I understand the basis for this decision.

We claim that the expansion isn't considered as some force or power. So as there is no need for force, there is no room for "moving away" only a "receding".

Therefore, by adding this simple word - "receding" instead of "moving away", we have bypassed this contradiction and now we can hold the stick from both sides.

In one hand - we can claim that nothing can move faster than the speed of light, while on the other hand we can justify why galaxies are receding from us at a speed which is greater than the speed of light.

 

And now - for the main question about the expansion:

 

How could it be that the matrix expansion of space comes for free?

If I want to make even one step - I need to set power.

So how could it be that the nature carries galaxies at a speed which is greater than the speed of light for free - without any need for power?

Don't you think that there must be a power source for that expansion?

[Mordred]

I reaaly don't know what it will take to make you understand.

 

Expansion does not cause inertia change. Recession velocity is NOT A TRUE VELOCITY it does not involve inertia change via f=ma.

 

No force acts upon the galaxies due to expansion so it does not violate the speed limit.

 

Every individual Mpc expands at the same rate

70 km/sec/Mpc. that is the expansion rate at every point in space. It is only when you add up a large number of individual Mpcs that you accumulate to greater than c recessive velocity.

 

Ie via Hubbles law. The Greater the seperation distance the greater the recessive velocity but if you could magically teleport to a far away galaxy its expansion rate at that Mpc will be 70 km/s/Mpc.

Edited April 28, 2017 by Mordred

[geordief]

Well is this expansion driven by any energetic process?

I don't mean in an ongoing way but at the outset.

I think inflation is supposed to have preceded expansion so I am asking about inflation.

Are inflation and expansion the same process in essence or are they actually different beasts?

Did inflation "merge" into expansion?

Edited April 28, 2017 by geordief

[Strange]

Now we understand the difference between "Moving away" and "receding".

 

 

Apparently not.

 

 

 

 

If I understand it correctly:

 

As always, you don't.

 

 

Based on the current hypothesis - nothing can move faster than a speed of light.

So in order to bypass that "nothing can move faster" we call it receding.

 

You have that exactly backwards, as so often.

 

The mathematics makes a clear distinction between local phenomena that can be simply described by special relativity, and more complex phenomena that require general relativity to describe them.

 

To try and help you understand this, we have characterised the former as "relative motion" and the latter as "recessional speed". As expected, you have got a firm grasp of the wrong end of the stick.

 

 

 

How could it be that the matrix expansion of space comes for free?

 

Because, counter to intuition, the normal state is that things experiencing no force will tend to move apart. That is just the way space-time works.

 

It requires a force, and potentially an expenditure of energy, to stop that expansion.

 

(p.s. metric expansion)

[pzkpfw]

... So how could it be that the nature carries galaxies at a speed which is greater than the speed of light for free ...

 

Just to illustrate metric expansion. Say these letters are galaxies and the hyphens are the space between them:

 

A-B-C-D-E-F-G-H-I-J-K-L-M

 

Note that M is 12 x "-" away from A.

 

After some time, space has expanded:

 

A---B---C---D---E---F---G---H---I---J---K---L---M

 

Now, M is 36 x "-" away from A.

 

That seems a lot:

 

| . . . . . . |

A-B-C-D-E-F-G-H-I-J-K-L-M |

A---B---C---D---E---F---G---H---I---J---K---L---M

 

... from the point of view of A, M is now (apparently) "moving" very fast (it moves 18 hyphens in one unit of time). But perspective, or point of view, is still relevant here. Take the view from L:

 

|.|

A-B-C-D-E-F-G-H-I-J-K-L-M |

A---B---C---D---E---F---G---H---I---J---K---L---M

 

... not such a big deal, according to L, M moves 2 hyphens in one unit of time; that's a lot less than 18 ... there's no point being incredulous about that (apparent) "speed" of 18 from the point of view of A.

 

 

As to why/how the Universe is expanding, that's a topic that deserves its own thread.

[David Levy]

Expansion does not cause inertia change. Recession velocity is NOT A TRUE VELOCITY it does not involve inertia change via f=ma.

No force acts upon the galaxies due to expansion so it does not violate the speed limit.

In the following article it is stated:

http://www.iflscience.com/space/why-universe-accelerating/

 

"We know that our universe is expanding at an accelerating rate, but what causes this growth remains a mystery. The most likely explanation is that a strange force dubbed “dark energy” is driving it."

 

So, the expansion is based on some sort of power/force/energy.

We must find the source for that energy

 

Just to illustrate metric expansion. Say these letters are galaxies and the hyphens are the space between them:

A-B-C-D-E-F-G-H-I-J-K-L-M

Note that M is 12 x "-" away from A.

After some time, space has expanded:

A---B---C---D---E---F---G---H---I---J---K---L---M

 

Thanks

That is excellent description for what we see.

However, what is the real cause for this phenomenon?

Let's look at the example which Janus has used:

A is an observer with a clock.

B is an observer with his own clock passing A an at the rear of a rocket moving at 0.6c relative to A, by B's measurements, the rocket is 0.6 light seconds long and there is a clock at the front which is synced to his own.

C is a projectile fired by B at 0.6c relative to himself towards the front of the rocket. He fires the projectile at the moment he is passing A.

Thus at the start, A,B, and C are co-located.

 

So, let's use the rockets as follow:

B is an observer with his own clock passing A at the rear of a rocket moving at 0.6c relative to A,

C is a projectile fired by B at 0.6c relative to himself towards the front of the rocket. He fires the projectile at the moment he is passing A.

D is a projectile fired by C at 0.6c relative to himself towards the front of the rocket. He fires the projectile at the moment he is passing A.

E is a projectile fired by D at 0.6c relative to himself towards the front of the rocket. He fires the projectile at the moment he is passing A.

….

 

M is a projectile fired by L at 0.6c relative to himself towards the front of the rocket. He fires the projectile at the moment he is passing A.

Hence.

At t=0 we get:

A

B

C

D

E

F

G

H

I

J

K

L

M

At t=1 we get:

A-B-C-D-E-F-G-H-I-J-K-L-M

At t=3 we get:

A---B---C---D---E---F---G---H---I---J---K---L---M

Hence, if the expansion works as rockets over rockets, than we have a simple solution.

Now we need to find the source for those rockets and/or the requested energy for the expansion.

Edited April 29, 2017 by David Levy

[Strange]

In the following article it is stated:[/size]

http://www.iflscience.com/space/why-universe-accelerating/[/size] [/size]

 

"We know that our universe is expanding at an accelerating rate, but what causes this growth remains a mystery. The most likely explanation is that a strange force dubbed “dark energy” is driving it."[/size]

 

So, the expansion is based on some sort of power/force/energy.[/size]

 

 

No. The acceleration appears to be driven by some sort of energy. The expansion happens naturally in the absence of any force.

 

Hence, if the expansion works as rockets over rockets, than we have a simple solution.

 

It doesn't.

 

To be more specific, velocities don't add linearly and so the speeds of each rocket will not increase at the same rate.

 

A---B---C---D---E---F---

v = 0 0.6 0.88 0.97 0.99 ...

 

 

Edited April 29, 2017 by Strange

[geordief]

 

 

As to why/how the Universe is expanding, that's a topic that deserves its own thread.

I think this recent one might cover that territory....

 

http://www.scienceforums.net/topic/101133-during-inflation-how-did-spacetime-push-particles/page-2?hl=inflation

[pzkpfw]

...

Hence, if the expansion works as rockets over rockets, than we have a simple solution.

...

No. If expansion gave actual-moving-through-space-speed, the furthest galaxies wouldn't be receding faster than light, as we know velocities don't add that way.

 

Metric expansion of space is different.

[David Levy]

Please try to answer the following contradiction:

 

In one hand it is stated that: "Every individual Mpc expands at the same rate 70 km/sec/Mpc"

 

 

Every individual Mpc expands at the same rate 70 km/sec/Mpc. that is the expansion rate at every point in space. It is only when you add up a large number of individual Mpcs that you accumulate to greater than c recessive velocity.

Ie via Hubbles law. The Greater the seperation distance the greater the recessive velocity but if you could magically teleport to a far away galaxy its expansion rate at that Mpc will be 70 km/s/Mpc.

 

Hence, the speed increases very linearly:

At 1 Mpc the speed is 70 Km/sec

At 10 Mpc the speed is 700 Km/sec

At 100 Mpc the speed is 7,000 Km/sec

At 1,000 Mpc the speed is 70,000 Km/sec

At 10,000 Mpc the speed is 700,000 Km/sec

and so on…

 

However, on the other hand based on Lorentz Transformations mathematics the speed increase isn't linearly

 

 

To be more specific, velocities don't add linearly and so the speeds of each rocket will not increase at the same rate.

A---B---C---D---E---F---
v = 0 0.6 0.88 0.97 0.99 ...

 

Can you please explain this contradiction?

Edited April 29, 2017 by David Levy

[Strange]

Can you please explain this contradiction?

 

 

Because Lorentz Transforms are part of SPECIAL relativity that only applies locally in flat space.

 

The expansion of space is described by GENERAL relativity.

 

(How many times have you been told this, now?)

Edited April 29, 2017 by Strange

[David Levy]

Because Lorentz Transforms are part of SPECIAL relativity that only applies locally in flat space.

The expansion of space is described by GENERAL relativity.

(How many times have you been told this, now?)

 

Thanks

 

So, Lorentz Transforms are part of SPECIAL relativity that only applies locally in flat space, while the expansion of space is described by GENERAL relativity.

 

Can you please specify the distance range for SPECIAL relativity and GENERAL relativity?

In other words, what is the maximal distance range that it is considered as SPECIAL relativity and therefore Lorence transformation is applicable? – (Which means velocities don't add linearly)

From what distance range it is considered as general relativity? (Which means velocities add linearly - Every individual Mpc expands at the same rate 70 km/sec/Mpc)

[Mordred]

Please try to answer the following contradiction:

 

In one hand it is stated that: "Every individual Mpc expands at the same rate 70 km/sec/Mpc"

 

 

 

Hence, the speed increases very linearly:

At 1 Mpc the speed is 70 Km/sec

At 10 Mpc the speed is 700 Km/sec

At 100 Mpc the speed is 7,000 Km/sec

At 1,000 Mpc the speed is 70,000 Km/sec

At 10,000 Mpc the speed is 700,000 Km/sec

and so on

 

However, on the other hand based on Lorentz Transformations mathematics the speed increase isn't linearly

 

 

 

Can you please explain this contradiction?

There is no contradiction between local dynamics per Mpc and the accumulated global expansion. The latter is a direct result of the first.

 

Try and exercise a little math. You certainly know how to add.

 

Add 70/km/c/Mpc 4400 times. At this point the recessive velocity will start to reach c. Add another 500 Mpc with its corresponding 70 km/s/Mpc rate and your recessive velocity will be greater than c.

[Strange]

 

Thanks

 

So, Lorentz Transforms are part of SPECIAL relativity that only applies locally in flat space, while the expansion of space is described by GENERAL relativity.

 

Can you please specify the distance range for SPECIAL relativity and GENERAL relativity?

In other words, what is the maximal distance range that it is considered as SPECIAL relativity and therefore Lorence transformation is applicable? – (Which means velocities don't add linearly)

From what distance range it is considered as general relativity? (Which means velocities add linearly - Every individual Mpc expands at the same rate 70 km/sec/Mpc)

 

 

There is no "distance range".