Has Geocentrism become less popular?

[JohnEmmett]

…

 

[FireDragon76]

Not that it is particularly relevant, but I've noticed a form of heliocentrism still evident in the reasoning of cosmologists, as they seem to measure everything by degree of redshift relative to ourselves. That may not be a fair statement if left without mention of the other things they DO take into account, but it still strikes me, all the same.

It has to do with relativity. The universe doesn't have a geographic center to measure from.

 

[Astrophile]

Amongst other pieces of nonsense in this video is the claim the Sun and Moon are also flat which raises a question regarding the Moon.
Libration completely destroys this idea.

Observations of sunspots as they move across the Sun's disc completely destroy the idea that the Sun is flat.

 

[Aaron112]

The earth APPEARS geocentric, but is not.

Einstein recently (the last century) said it well could be. The top ten or twelve math-maticians on earth agreed.

 

[sjastro]

Einstein recently (the last century) said it well could be. The top ten or twelve math-maticians on earth agreed.

​

Care to name these top ten or twelve mathematicians???

 

[Aaron112]

Care to name these top ten or twelve mathematicians???

Their names were given or not given in the reports about Einstein correctly and accurately quoted in news items years ago.

 

[sjastro]

Their names were given or not given in the reports about Einstein correctly and accurately quoted in news items years ago.

????
So on other words you cannot back up your claims with this illogical response.
Let's look at the science.
When Einstein came up with the general theory of relativity one of the first verifications of the theory suggested by Einstein himself was it explained the perihelion advance in Mercury's orbit around the Sun.
For Einstein to even consider geocentricism is complete utter rubbish along with the top ten or twelve mathematicians you can't even name.

 

[Astrophile]

Yeah, I understood distances, but, for eg, it doesn't make sense to me how, if, let's say, "east" of us a galaxy is receding (relative to us) at, let's say, 1/4 the speed of light, and "west" of us, another is receding relative to us at 1/4 the speed of light, how an observer in the one galaxy would see the other galaxy with the same degree of redshift that we do. But maybe that isn't what you were saying. I do see how very distant galaxies might seem about the same for any Milky Way observer, or maybe even any observer in our local galaxy cluster.

The two galaxies, supposing each to be receding relative to us, at 3/4 the speed of light, should be, according to intuition, be receding relative to each other, at more than the speed of light. But people keep telling me it is impossible to exceed the speed of light. I keep wanting to ask them, "The speed of light relative to WHAT?" THAT, I still do not understand.

No, you have misunderstood the situation. If there were two galaxies, in opposite directions as seen from the Earth, both receding at 1/4 the speed of light, from either of those two galaxies the other would be receding at about half the speed of light, and our galaxy (the Milky Way) would be receding at 1/4 the speed of light.

If the two galaxies were each receding from the Milky Way at 3/4 of the speed of light, from either of these two galaxies the other would be receding at more than 3/4 of the speed of light. You would need to understand relativistic cosmology to be able to calculate the apparent recession speed of one galaxy relative to the other.

 

[Mark Quayle]

If the two galaxies were each receding from the Milky Way at 3/4 of the speed of light, from either of these two galaxies the other would be receding at more than 3/4 of the speed of light. You would need to understand relativistic cosmology to be able to calculate the apparent recession speed of one galaxy relative to the other.

I must not have been clear.

I'm asking, now, if one galaxy is receding from us at 3/4 the speed of light relative to us, while another is receding from us in the opposite direction at 3/4 the speed of light relative to us, how are they not achieving 1.5 times the speed of light relative to each other?

 

[Bradskii]

I must not have been clear.

I'm asking, now, if one galaxy is receding from us at 3/4 the speed of light relative to us, while another is receding from us in the opposite direction at 3/4 the speed of light relative to us, how are they not achieving 1.5 times the speed of light relative to each other?

They're not moving*. It's the space inbetween them which is expanding. To use the old balloon analogy, if you put two marks on a balloon and then blow it up, the two marks (galaxies) are in exactly the same spot on the balloon (space). But the distance between them is getting greater.

*They'll definitely be moving but assume for the purpose of the exercise that they are not. They actually may be moving towards each other but still getting further apart.

And if you have three dots on the balloon then the two furthest apart will be moving away from reach other faster than the two losest together. So distant galaxies are receding faster than closer ones. And you get to a point when the expansion, as you pointed out, is greater than the speed of light. So they literally dissapear. Nothing happening there will ever be available to us. That distance is the radius of the observable universe - about 46 billion light years. Observable because anything outside it is unobservable.

 

[Mark Quayle]

They're not moving*. It's the space inbetween them which is expanding. To use the old balloon analogy, if you put two marks on a balloon and then blow it up, the two marks (galaxies) are in exactly the same spot on the balloon (space). But the distance between them is getting greater.

*They'll definitely be moving but assume for the purpose of the exercise that they are not. They actually may be moving towards each other but still getting further apart.

Of course. But my description is that they are moving apart at that speed relative to us, and being in opposite directions, at double that speed relative to each other. The question is not whether they are moving our direction relative to some other object.

And if you have three dots on the balloon then the two furthest apart will be moving away from reach other faster than the two losest together. So distant galaxies are receding faster than closer ones. And you get to a point when the expansion, as you pointed out, is greater than the speed of light. So they literally dissapear. Nothing happening there will ever be available to us. That distance is the radius of the observable universe - about 46 billion light years. Observable because anything outside it is unobservable.

That makes sense. So, if the expansion between objects can be greater than the speed of light, why do they say that nothing can exceed the speed of light? Is not the question, "relative to what?", incoherent here?

 

[Bradskii]

Of course. But my description is that they are moving apart at that speed relative to us, and being in opposite directions, at double that speed relative to each other. The question is not whether they are moving our direction relative to some other object.

Again, they are not moving through space. They could well be static. But the space is expanding. And the further apart two objects are, the faster is the distance between them expanding. So you could look in one direction and it would appear that galaxy A is moving away from us at 0.75 the speed of light. Look in the other direction and you'd see another galaxy B doing exactly the same. But...if you were standing somewhere in galaxy A then the space between you and B is expanding faster than the speed of light can cross it. So light from B would never reach you.

That makes sense. So, if the expansion between objects can be greater than the speed of light, why do they say that nothing can exceed the speed of light? Is not the question, "relative to what?", incoherent here?

Speed equals distance/time. So something has to move X distance through space relative to any given point over time T to get a speed of X/T, relative to the given point. Both galaxies could be static. They aren't moving (they will be moving in some direction but assume they are not). Just like the dots on the balloon. So their speed relative to any other static object is zero. But...the distance between them is getting bigger.

 

[Mark Quayle]

Again, they are not moving through space. They could well be static. But the space is expanding. And the further apart two objects are, the faster is the distance between them expanding. So you could look in one direction and it would appear that galaxy A is moving away from us at 0.75 the speed of light. Look in the other direction and you'd see another galaxy B doing exactly the same. But...if you were standing somewhere in galaxy A then the space between you and B is expanding faster than the speed of light can cross it. So light from B would never reach you.

Speed equals distance/time. So something has to move X distance through space relative to any given point over time T to get a speed of X/T, relative to the given point. Both galaxies could be static. They aren't moving (they will be moving in some direction but assume they are not). Just like the dots on the balloon. So their speed relative to any other static object is zero. But...the distance between them is getting bigger.

Not meaning to disparage, nor even saying I'm right, but that sounds like simple double-talk to me. And what is a static object? I mean, how can you say that any object in space is actually static? It's only a comparative statement, no?

One (to me) seeming-implication though, raised by your description, is that if space is expanding the objects in space should also be expanding, the very smallest particle expanding also, which expansion would be undetectable . But either way, it still sounds like the objects on the 'surface' of the expansion are nevertheless moving away from each other, at some speed relative to each other, and therefore (as we suppose) A may move relative to B at more than the speed of light and thus be invisible to B.

 

[Bradskii]

Not meaning to disparage, nor even saying I'm right, but that sounds like simple double-talk to me. And what is a static object? I mean, how can you say that any object in space is actually static? It's only a comparative statement, no?

One (to me) seeming-implication though, raised by your description, is that if space is expanding the objects in space should also be expanding, the very smallest particle expanding also, which expansion would be undetectable . But either way, it still sounds like the objects on the 'surface' of the expansion are nevertheless moving away from each other, at some speed relative to each other, and therefore (as we suppose) A may move relative to B at more than the speed of light and thus be invisible to B.

I know this is difficult to grasp, but galaxies aren't necessarily moving away from each other, but the distance between them is increasing.

This is a good article that describes it: This Is Why We Aren't Expanding, Even If The Universe Is

And it explains that other forces come into play at smaller distances. Such as gravity. So local expansion doesn't happen.

 

[Mark Quayle]

I know this is difficult to grasp, but galaxies aren't necessarily moving away from each other, but the distance between them is increasing.

This is a good article that describes it: This Is Why We Aren't Expanding, Even If The Universe Is

And it explains that other forces come into play at smaller distances. Such as gravity. So local expansion doesn't happen.

Begs the question, if we are expanding, how would we know!

I'll check out the article. Thanks.

 

[Mark Quayle]

I know this is difficult to grasp, but galaxies aren't necessarily moving away from each other, but the distance between them is increasing.

This is a good article that describes it: This Is Why We Aren't Expanding, Even If The Universe Is

And it explains that other forces come into play at smaller distances. Such as gravity. So local expansion doesn't happen.

Ok, I read it, and I can understand what it says about the local distances not expanding, but I still don't get it. The fact that the expansion seems to be itself accelerating can only (so far as I understood) observed, but not explained. In a 3-d grid universe, this could still happen, it seems to me. The fact we can't explain it doesn't mean we have to get fancy. In fact, some of the conjectures I see could also apply in 3-d space. But, I agree that I just don't get it. I'll read it again, and try to follow the differences, but so far, it sounds like double-talk.

 

[Shemjaza]

Ok, I read it, and I can understand what it says about the local distances not expanding, but I still don't get it. The fact that the expansion seems to be itself accelerating can only (so far as I understood) observed, but not explained. In a 3-d grid universe, this could still happen, it seems to me. The fact we can't explain it doesn't mean we have to get fancy. In fact, some of the conjectures I see could also apply in 3-d space. But, I agree that I just don't get it. I'll read it again, and try to follow the differences, but so far, it sounds like double-talk.

Before the Theory of Relativity we had already begun to discover physical anomalies that are explained by it and not by regular Newtonian physics, like the orbit of Mercury. In the modern world the readings and time data of accurate global positioning satellites also feature anomalies consistent with relativistic effects.

This all adds credence to conclusion that space itself is a kind of substance that is effected by the rest of the physical world and shows the difference between relative velocity through space and the detected effects of expansion.

 

[sjastro]

Ok, I read it, and I can understand what it says about the local distances not expanding, but I still don't get it. The fact that the expansion seems to be itself accelerating can only (so far as I understood) observed, but not explained. In a 3-d grid universe, this could still happen, it seems to me. The fact we can't explain it doesn't mean we have to get fancy. In fact, some of the conjectures I see could also apply in 3-d space. But, I agree that I just don't get it. I'll read it again, and try to follow the differences, but so far, it sounds like double-talk.

The two pieces of evidence which support metric expansion of distant non gravitationally bound galaxies instead of galaxies moving in space are;

(1) The galaxies are moving along the line of sight of the observer there is no transverse or perpendicular component of motion relative to the observer.
(2) The recession velocity v is proportional to distance x, the proportionality constant being Hubble’s constant H, v = Hx.
This is Hubble’s law.

In the case of point (1), if all galaxies move in space instead of metric expansion, then we would expect to also observe a transverse or perpendicular component of motion even in the most distant galaxies as a deviation from the straight line relationship for Hubble’s law.
In fact, there is no reason to even suggest recession velocities should occur exclusively, in our Local Group not only do transverse motions occur but the spectra of galaxies such as the Andromeda galaxy are blue shifted indicating they are approaching the observer not receding.

For point (2) the straight line relationship between velocity and distance is exclusively a property of metric expansion, there is no way we can even show mathematically how a straight line relationship for velocity and distance can occur for galaxies accelerating through space.
We can show this by using the simplest example of constant acceleration at non relativistic speeds using calculus and high school physics.
Since the acceleration a is constant for the velocity v at time t and using the initial conditions v=0 at x=0 for a Big Bang condition.

The general graph for constant acceleration at non relativistic speeds in space does not have a straight line relationship as shown.

For more complicated cases such as non constant acceleration and/or relativistic speeds the graphs are far more complex.