Lorentz Transformations (split from why nothing >c)

[pzkpfw]

Is there any speed related to this expansion? I understand it is unrelated **to c but is it ,at least in theory possible to describe the rate at which this expansion is ongoing?

 

Is there a theoretical upper limit to this expansion and does it have to be a globalized effect? Is it ,at least in theory possible that their might be localized instances of expansion ?

 

**or is "unrelated" too strong and is there actually a formula that connects the two rates?

Some of that's covered in the linked Universe Today article. (I'd suggest looking into inflation also, for a period of faster expansion. https://en.wikipedia.org/wiki/Inflation_(cosmology))

 

The rest is perhaps a bit speculative, and maybe deserves a thread of its own.

Edited April 25, 2017 by pzkpfw

[geordief]

Some of that's covered in the linked Universe Today article. (I'd suggest looking into inflation also, for a period of faster expansion. https://en.wikipedia.org/wiki/Inflation_(cosmology))

 

The rest is perhaps a bit speculative, and maybe deserves a thread of its own.

The inflation article seems exponentially more involved than the "simple " expansion one. I doubt I could learn much from it at this stage as it seems to requite a lot more basic understandings than I have for now.

 

Thanks all the same.

Edited April 25, 2017 by geordief

[David Levy]

Current science is very clear. e.g. https://www.universetoday.com/122768/how-are-galaxies-moving-away-faster-than-light/

 

Great article!

However, there is a contradiction, as you have stated:

 

i.e. Nothing is moving through space faster than c, but, due to expansion of the Universe very distant objects are getting further away, faster than c.

 

In one hand it is stated: that that galaxies which are located at a distance of over 13.7 Billion light years should move faster than a speed of light:

"This is our freaky friend, the Hubble Constant, the idea that for every megaparsec of distance between us and a distant galaxy, the speed separating them increases by about 71 kilometers per second.

Galaxies separated by 2 parsecs will increase their speed by 142 kilometers every second. If you run the mathatron, once you get out to 4,200 megaparsecs away, two galaxies will see each other traveling away faster than the speed of light. How big Is that, is it larger than the Universe?

The first light ever, the cosmic microwave background radiation, is 46 billion light-years away from us in all directions. I did the math and 4,200 megaparsecs is a little over 13.7 billion light-years.There’s mountains of room for objects to be more than 4,200 megaparsecs away from each other. Thanks Universe?!?"

 

While on the other hand it is stated:

"I stand with Einstein when I say that nothing can move faster than light through space, but objects embedded in space can appear to expand faster than the speed of light depending on your perspective.

"Light emitted by the galaxies is moving towards us, while the galaxy itself is traveling away from us, so the photons emitted by all the stars can still reach us. These wavelengths of light get all stretched out, and duckslide further into the red end of the spectrum, off to infrared, microwave, and even radio waves. Given time, the photons will be stretched so far that we won’t be able to detect the galaxy at all.

In the distant future, all galaxies and radiation we see today will have faded away to be completely undetectable. Future astronomers will have no idea that there was ever a Big Bang, or that there are other galaxies outside the Milky Way. Thanks Universe."

 

So, it is clear that we want to hold the stick in both sides simultaneously.

In one hand we claim that nothing can move faster than the speed of light but on the other hand we are asking for some help from our dear "expansion" as it is stated:

"but objects embedded in space can appear to expand faster than the speed of light depending on your perspective"

So, we say yes and no simultaneously..

 

Hence, although it's quite difficult for us to say yes or no – it's time to give direct answer.

Not just to me, but mainly to yourself.

 

It's a very sad "technique" to ask oversimplified questions and try to "trap" people into simple answers looking for a "gotcha".

This answer has not changed since the first five times you asked it.

 

Than with the expansion or without - somehow they must move faster than the speed of light with reference to our prospective.

This must be embedded in our formula.

How can we say that the formula is correct "but...

There is no room for "but".

Just "yes" or "no" - please!

 

If due to the expansion some galaxies can move faster than a speed of light depending on our perspective - than please say yes and show it in an updated formula!

We MUST add the impact of the expansion to our formula.

Edited April 25, 2017 by David Levy

[Strange]

Thanks

 

I'm not sure that I fully understand your answer with regards to the expansion.

 

So, please advice if the following is correct:

1. The expansion has no impact this formula. Hence, the formula is fully updated for our current universe.

2. Therefore, there is no galaxy in the whole universe which is moving away from us at a speed which is faster than the speed of light (even if it is located 40 or 100 Billion Light years away from us.

Yes or no

1. Yes

2. No

Is there any speed related to this expansion? I understand it is unrelated **to c but is it ,at least in theory possible to describe the rate at which this expansion is ongoing?

Expansion is a scaling effect.

The "speed" of expansion is proportional to how far away you look. At the Hubble distance the speed is c. Beyond that it is greater then c (and we can see galaxies receding at more than c).

[imatfaal]

 

....

We MUST add the impact of the expansion to our formula.

 

No, we MUST NOT. In the situations in which it is used it is great. You should try some actual study before making pronouncements. At the beginning of this thread, it was clear that you had no idea of the concepts of Special relativity (you claimed the absolute nature of time and distance remember?) - by post#53 you are demanding the equations be re-written. I have counted at least three knowledgeable and helpful members explaining to you the difference between a metric expansion and relative motion through space; you seem to hurry through the carefully prepared posts in your rush to find yet more things you can say must change about modern physics.

[Strange]

Well, you could say that the "updated formula" is GR, and specifically the FLRW metric.

[Mordred]

The inflation article seems exponentially more involved than the "simple " expansion one. I doubt I could learn much from it at this stage as it seems to requite a lot more basic understandings than I have for now.

 

Thanks all the same.

I have a better article which covers this. It was written specifically with forum members as the target audience

 

http://tangentspace.info/docs/horizon.pdf :Inflation and the Cosmological Horizon by Brian Powell

 

Now lets look specifically why no inertia is imparted.

 

Inertia change requires work or force to be done to cause the inertia change ie f=ma.

 

The regions surrounding galaxies are homogeneous and isotropic so in essence uniform. (Cosmological principle)

 

So the force due to pressure surrounding every galaxy is uniform.

 

How can that galaxy gain inertia due to expansion if there is no differences in the amount of pressure on any facing?

 

The answer is its impossible, instead the metric changes

[geordief]

 

Expansion is a scaling effect.

The "speed" of expansion is proportional to how far away you look. At the Hubble distance the speed is c. Beyond that it is greater then c (and we can see galaxies receding at more than c).

Is there an "absolute" measure of the scaling and is there any theoretical limit to how "fast" the scaling process can proceed?

 

I mean ,c is there because there has to be a maximum speed of some value (in my view) but,separately does there have to be a limit to the scaling effect?

 

It is driven by some energetic process isn't it?

 

I know that it causes an separation that is faster the further away one is from what it is one observes but there is an underlying mechanism

to which one might attribute a "speed" or "rate" and this should presumably (verifiably?) be the same in all parts of the observable universe.

I have a better article which covers this. It was written specifically with forum members as the target audience

 

http://tangentspace.info/docs/horizon.pdf :Inflation and the Cosmological Horizon by Brian Powell

 

Now lets look specifically why no inertia is imparted.

 

Inertia change requires work or force to be done to cause the inertia change ie f=ma.

 

The regions surrounding galaxies are homogeneous and isotropic so in essence uniform. (Cosmological principle)

 

So the force due to pressure surrounding every galaxy is uniform.

 

How can that galaxy gain inertia due to expansion if there is no differences in the amount of pressure on any facing?

 

The answer is its impossible, instead the metric changes

We cross posted . I will have to look at your post. It looks complicated at first glance.

[Mordred]

Its as low math as feasible to be informative. However I will answer you last question.

 

Metric expansion is not limitted by the speed limit of GR as it does not involve velocity change or inertia. (its strictly a volume change not kinematic motion)

Edited April 25, 2017 by Mordred

[geordief]

Its as low math as feasible to be informative. However I will answer you last question.

 

Metric expansion is not limitted by the speed limit of GR as it does not involve velocity change or inertia. (its strictly a volume change not kinematic motion)

No I wasn't questioning that . I was wondering if it might have its own intrinsic"speed limit" (or "rate limit" ) entirely separate to the speed limit of GR.

 

Naively it seems more fundamental than the GR speed limit. (maybe "fundamental" implies a hierarchy that does not exist)

[imatfaal]

No I wasn't questioning that . I was wondering if it might have its own intrinsic"speed limit" (or "rate limit" ) entirely separate to the speed limit of GR.

 

Naively it seems more fundamental than the GR speed limit. (maybe "fundamental" implies a hierarchy that does not exist)

 

There will be a distance / sphere beyond which we presume lie stars/galaxies/clusters etc which we have never been causally connected to and which we have never/will never see any light from; I think this is correct*. There will be an associated rate of expansion between us and something at that distance/on that sphere - whilst it is not a physical limit it is a point at which expansion becomes meaningless as nothing we will ever have any inkling of will ever have a higher rate.

 

* Hopefully Mordred can tell me if this is true - in the meantime I will do a little more reading. Galaxies which we will one day see because of expansion is a - to me at least - a counter intuitive subject. I am pretty sure this is the particle horizon at 14.4Gpc - although I had a feeling that expansion for some odd reason meant that eventually we might see more although this sounds like rubbish

[Strange]

Is there an "absolute" measure of the scaling and is there any theoretical limit to how "fast" the scaling process can proceed?

 

 

The scale factor is a dimensionless number so I suppose it is absolute in some sense. There is, as far as I know, no theoretical upper limit to the rate at which the universe expands. During ht inflationary period it was very large (Mordred can probably put a figure on that!)

Than with the expansion or without - somehow they must move faster than the speed of light with reference to our prospective.

This must be embedded in our formula.

How can we say that the formula is correct "but...

There is no room for "but".

Just "yes" or "no" - please!

 

 

The need for a "but" comes from your ignorance.

 

 

If due to the expansion some galaxies can move faster than a speed of light depending on our perspective - than please say yes and show it in an updated formula!

We MUST add the impact of the expansion to our formula.

 

You MUST learn the basics before assuming that you are right and hundreds of years of physics are wrong. Again.

 

The speed limit of the speed of light comes from special relativity. Which means that it is a local limit (in flat space, with no gravity, in inertial frames of reference). It just doesn't apply in cases that have to be described using general relativity (such as cosmological expansion).

[Mordred]

Your in essence correct there are causally disconnected regions beyond the Cosmological event horizon. Those causally disconnected regions will never become causally connected on the future unless they were causally connected at one time in the past.

 

Inflation in solving the horizon problem connected previously disconnected regions but this is an extreme example that runs counter to the above.

 

So unless we have another inflationary scale event its unlikely to connect to further causal disconnected regions afiak.

 

Sometime in the future galaxies we see today will become causally disconnected never to be seen again.

 

The other problem is that we can now see the surface of last scattering which is the furthest we will ever see until we can measure the cosmic neutrino background. This then will be the new and furthest possible extent we will ever see. The neutrino background will allow us to see past the opaque fog prior to recombination.

Edited April 25, 2017 by Mordred

[imatfaal]

Your in essence correct there are causally disconnected regions beyond the Cosmological event horizon. Those causally disconnected regions will never become causally connected on the future unless they were causally connected at one time in the past.

 

Inflation in solving the horizon problem connected previously disconnected regions but this is an extreme example that runs counter to the above.

 

So unless we have another inflationary scale event its unlikely to connect to further causal disconnected regions afiak.

 

Sometime in the future galaxies we see today will become causally disconnected never to be seen again.

 

The other problem is that we can now see the surface of last scattering which is the furthest we will ever see until we can measure the cosmic neutrino background. This then will be the new and furthest possible extent we will ever see. The neutrino background will allow us to see past the opaque fog prior to recombination.

Thanks Mordred - it was the inflationary period section that I was partially remembering. And yes regarding surface of last scattering - but I was thinking in terms of any possibility of connexion; neutrino, gravitational wave etc

[David Levy]

Thanks

Great answer

 

The speed limit of the speed of light comes from special relativity. Which means that it is a local limit (in flat space, with no gravity, in inertial frames of reference).

 

Fully Agree!

 

It just doesn't apply in cases that have to be described using general relativity (such as cosmological expansion).

 

Also fully agree.

So, due to general relativity (such as cosmological expansion), there is no speed limit of speed of light and therefore, galaxies could move at a speed which is higher than the speed of light.

Did I understand you correctly?

 

Edited April 26, 2017 by David Levy

[Mordred]

Forget move movement implies inertia. The volume change doesn't impart inertia. The galaxies will never gain a speed greater than c. Do you understand what kinematic motion means?

Edited April 26, 2017 by Mordred

[David Levy]

The galaxies will never gain a speed greater than c.

 

So at any location in the whole universe galaxies will never ever gain a speed greater than c. This is based on special relativity

Therefore, when we look at our nearby space, all the galaxies must move at a speed which is lower than the speed of light.

However, If we look at the horizon, we see galaxies which are moving away from us at a speed which is close to the speed of light.

Never the less, if we could be there we should see a similar space view as we see from our milky way galaxy.

Hence, as stated: "Which means that it is a local limit (in flat space, with no gravity, in inertial frames of reference)."

So far so good.

 

Forget move movement implies inertia. The volume change doesn't impart inertia.

 

 

Now, let's focus on general relativity by the following example:

Let's assume that our galaxy is just standing at our position (with regards to the nearby space aria).

40 Billion Light years away - there is a galaxy which also just stands at its local space aria.

However, due to the expansion, the volume between the two galaxies increases dramatically.

Hence, based on a simple calculation, the two galaxies are actually moving away from each other at a speed which is greater than the speed of light.

That is based on my simple common sense.

However, based on kinematic motion this is impossible.

 

 

Do you understand what kinematic motion means?

 

I really can't understand why.

Edited April 26, 2017 by David Levy

[Strange]

Now, let's focus on general relativity by the following example:

Let's assume that our galaxy is just standing at our position (with regards to the nearby space aria).

40 Billion Light years away - there is a galaxy which also just stands at its local space aria.

However, due to the expansion, the volume between the two galaxies increases dramatically.

Hence, based on a simple calculation, the two galaxies are actually moving away from each other at a speed which is greater than the speed of light.

 

 

The difference is that neither galaxy is actually moving "through space"; the separation is due to increase in the amount of space between them.

 

One way of seeing this is to consider the fact that as the distance increases then the speed of separation increases but there is no acceleration. You can tell this is the case, because acceleration means a force is applied (you can tell when your car accelerates because you are pushed back into your seat) and there is no fore in this case.

[Delta1212]

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.

[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.

 

Excellent!!!

I fully agree with your brilliant example.

Yes, yes - yes!

So, we are not moving faster than the speed of light but with regards to that far end galaxy we recede away from them at a speed faster than the speed of light.

Don't forget that everything is relative.

Hence, instead of using the word "moving" away, we need to use the word "recede" away.

I have no problem with that.

Now we can be friend again.

No more war!

 

One simple word, same meaning - bring peace to our universe.

Edited April 26, 2017 by David Levy

[robinpike]

The difference is that neither galaxy is actually moving "through space"; the separation is due to increase in the amount of space between them.

 

One way of seeing this is to consider the fact that as the distance increases then the speed of separation increases but there is no acceleration. You can tell this is the case, because acceleration means a force is applied (you can tell when your car accelerates because you are pushed back into your seat) and there is no fore in this case.

A small point, but to be pedantic... The absence of a 'feel' of acceleration isn't an absolute test that acceleration isn't occurring. For example, acceleration by gravity affects all the atoms in your body - free falling in space in a gravity field doesn't produce a feeling of acceleration.

 

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.

 

If I am understanding this correctly...

 

IF space were to be expanding at a constant rate, then the amount of separation between two galaxies is irrelevant, for the rate of separation between the two galaxies would remain the same. [in the escalator example above, when you run, either you can always reach the other person, or you can never reach the other person. The starting distance between you and the other person is irrelevant.]

 

So, even when the distance between the two galaxies is very large, with a constant rate of separation, and assuming a rate of separation less than the speed of light, then light can always reach any other object. The only impact of two galaxies being a great distance apart, is that the light will take longer to reach the other galaxy.

 

Please can some one step through the explanation of how expansion (whether at a constant rate or increasing over time) is able to prevent light from reaching a distant galaxy? I do not understand how that is possible.

[Strange]

A small point, but to be pedantic... The absence of a 'feel' of acceleration isn't an absolute test that acceleration isn't occurring. For example, acceleration by gravity affects all the atoms in your body - free falling in space in a gravity field doesn't produce a feeling of acceleration.

 

 

Which is because there is no force involved. (I was going to add this as another example, but had a horrible feeling it might just confuse David Levy). So, strictly speaking in free-fall you are not accelerating in GR terms. When you are sitting still in your chair and feel the chair pushing against you, that is when you are accelerating!

 

 

 

Please can some one step through the explanation of how expansion (whether at a constant rate or increasing over time) is able to prevent light from reaching a distant galaxy? I do not understand how that is possible.

 

Imagine a galaxy that is about 14 billion light years away when a photon is emitted. So the photon has 14 billion light years to travel. After 7 billion years, it should be half way, but in that time the distance to the galaxy has roughly doubled and so the photon, which has travelled half the distance, still has 14 billion light years to travel. After another 7 billion years, it has travelled half that distance but the distance has doubled again and so it still has 14 billion light years to go! And so on.

 

(Note that these numbers are for illustrative purposes only [as they say in adverts] or, in other words, wrong. But hopefully they illustrate the principle. You would need to integrate the expansion over the period of travel [i think] to get the right numbers.)

Edited April 26, 2017 by Strange

[geordief]

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?

[Delta1212]

A small point, but to be pedantic... The absence of a 'feel' of acceleration isn't an absolute test that acceleration isn't occurring. For example, acceleration by gravity affects all the atoms in your body - free falling in space in a gravity field doesn't produce a feeling of acceleration.

 

 

If I am understanding this correctly...

 

IF space were to be expanding at a constant rate, then the amount of separation between two galaxies is irrelevant, for the rate of separation between the two galaxies would remain the same. [in the escalator example above, when you run, either you can always reach the other person, or you can never reach the other person. The starting distance between you and the other person is irrelevant.]

 

So, even when the distance between the two galaxies is very large, with a constant rate of separation, and assuming a rate of separation less than the speed of light, then light can always reach any other object. The only impact of two galaxies being a great distance apart, is that the light will take longer to reach the other galaxy.

 

Please can some one step through the explanation of how expansion (whether at a constant rate or increasing over time) is able to prevent light from reaching a distant galaxy? I do not understand how that is possible.

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.

[Strange]

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?

 

 

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.)