Is the universe at least 136 billion years old, is the universe not expanding at all, did the universe begin its expansion when Hubble measured its redshift for the first time or was light twice as fast 13.5 billion years ago than it is today?

[swansont]

5 hours ago, tmdarkmatter said:

This is like the current explanation of gravity: "The only proof of space-time curvature is gravity and the only explanation for gravity is space-time curvature."

Is that an actual quote from someone? If so, who?

Or is it your summary of the situation? In which case it’s flawed. 

[Markus Hanke]

14 hours ago, tmdarkmatter said:

In that case why should we still think that the universe is expanding, if all the redshift can just be because of this "getting tired" effect?

I think you are forgetting several things here. First and foremost, what we are looking for in cosmology isn’t just an explanation for redshift - it’s a model that can explain all the available observational data in a coherent framework that is compatible with known physics. Of course cosmological redshift is a key data point, but there are other important observations:

- the cosmic microwave background and its polarisation

- the ratios of heavy and light elements (nucleosynthesis)

- the large-scale structure of the universe (filaments and voids)

- gravitational wave background (g-waves with wavelengths on the order ~Ly)

- acoustic baryonic oscillations

- the accelerated expansion rate

Among many others. Secondly, whatever model we use in cosmology must be fully compatible with the laws of gravity, since that is the predominant force on large scales. At present, this is General Relativity, which has been extensively tested on solar system scales, and found to be correct within that domain. We’re making a working assumption here that it remains equally valid on larger scales too.

Right now, the only model we know of that fits all these criteria really well is the Lambda-CDM model. It’s a valid solution to the gravitational field equations of GR for a certain set of reasonable conditions, and it provides the current best fit for the available observational data. Metric expansion is a natural part of this - it necessarily follows directly from the laws of gravity. 

This isn’t to say that Lambda-CDM is without its problems - there is a certain tension with some observational data, and there are a few things it struggles to explain at all. That is why a variety of alternative models have been (and continue to be) explored; see here for a very quick overview:

https://en.m.wikipedia.org/wiki/Non-standard_cosmology

But once all is considered, the Lambda-CDM model still remains the one model that provides the best fit to the largest set of currently available observational data, which is why it is the accepted consensus at present. But as more data becomes available to us, this may well change in the future - the last word is most likely not spoken here, especially since for now we can only observe the universe in the electromagnetic spectrum, and to some limited extent in the g-wave spectrum; the neutrino spectrum is as of yet almost entirely missing, since we haven’t got sensitive enough detectors. We’d expect to find a cosmic neutrino background with very specific properties as well, so this will be an important future test of our models.

So there’s a whole lot more going on in cosmology than just light and redshift - you can’t either embrace nor reject any model just on the basis of this alone.

[tmdarkmatter]

11 hours ago, swansont said:

Is that an actual quote from someone? If so, who?

Or is it your summary of the situation? In which case it’s flawed. 

Interesting that if this was an actual quote from "someone" it has a certain value, but if I am writing it, it must be flawed.

2 hours ago, Markus Hanke said:

- the accelerated expansion rate

Interesting that this is also only based on red shift as well as all the distances of the objects you are mentioning. Red shift is the main tool of this Lambda-CDM model so if we remove that tool, we would have to start from the beginning again. We would have to observe the furthest galaxies for millions of years to see if they get smaller (if they are moving away from us).

A question about this paper is, why are they not taking into account the rotation movement of earth? In the morning, when the observer is moving in the direction of the sun, there should be more blue shift and in the evening, when the observer is moving away from the sun, there should be more red shift of the light coming from the sun in this experiment. Or what am I doing wrong? Please tell me. Did they do all their measurements exactly at 12 p.m.? On the other hand, why would the moon have a gravitational force of zero?

2009.10558.pdf (arxiv.org)

Even the AI understands what I mean:

@Clyde should the rotation movement on earth have an effect on the measurement of the red shifting of galaxies?

Yes, the rotation movement of Earth can have a small effect on the measurement of the redshifting of galaxies due to the Doppler effect.

@Clyde should the movement of earth around the sun have an effect on the measurement ofr the redshifting of galaxies?

yes, the movement of Earth around the Sun can have a small effect on the measurement of the redshifting of galaxies due to the changing relative velocity between Earth and the observed galaxies.

@Clyde should the movement of the solar system around the center of the milky way have an effect on the measurement of the redshifting of galaxies?

yes, the movement of the solar system around the center of the Milky Way can have a small effect on the measurement of the redshifting of galaxies due to the changing relative velocity between our solar system and the observed galaxies.

Edited November 14, 2023 by tmdarkmatter

[Markus Hanke]

3 hours ago, tmdarkmatter said:

Red shift is the main tool of this Lambda-CDM model

As I said, it is only one single data point in among many others. There is really no “main” one, as they all need to fit.

[swansont]

3 hours ago, tmdarkmatter said:

Interesting that if this was an actual quote from "someone" it has a certain value, but if I am writing it, it must be flawed.

If it were a quote I’d want to know the context of it. In regards to this discussion, it’s flawed. And I notice you didn’t answer the question, or invite any discussion as to why it’s flawed (and it’s things like this that gets your threads closed; it’s soapboxing, which is against the rules)

It’s trivially wrong, as Newton had a model for gravity that did not invoke curvature.

It also contains a tautology, since the currently accepted model is spacetime curvature, but is it the only evidence? Models make specific predictions. Time dilation and bending light depend on a particular model, and not merely the existence of gravity.

And to echo what Markus says above, models are accepted based on all the evidence, not just one data point. Same goes for rejection of flawed models.

[tmdarkmatter]

I like to ask the AI about these topics because the AI has no prejudice:

@Clyde so gravity exists because of curvature of space-time and the only proof of space-time curvature is gravity? Clyde AI — 10/19/2023 9:29 PM that's correct. gravity is the result of space-time curvature, and the evidence for space-time curvature is the existence of gravity. it's a bit of a circular relationship.

Circular relationship? Lol

[Markus Hanke]

3 hours ago, tmdarkmatter said:

We would have to observe the furthest galaxies for millions of years to see if they get smaller (if they are moving away from us).

Redshift measurements are not done by observing anything “getting smaller”, so you don’t need to look for millions of years. Also, it’s not that things recede only from us - everything recedes from everything else. The distances between all systems not gravitationally bound will increase over time, equally in all directions. 

3 hours ago, tmdarkmatter said:

Or what am I doing wrong? Please tell me.

Well, it’s just that cosmological redshift is of a vastly greater magnitude than any local gravitational or kinematic effects - eg frequency shift due to the relative motion of galaxies is on the order z ~ 0.005 or so, whereas typical cosmological redshifts for very distant objects is of the order z ~ 10. That’s many orders of magnitude (due to the maths relations involved), so local effects such as the ones you mentioned can be safely ignored on very large scales.

 

[swansont]

AI is not a valid resource for science discussions. AI has no expertise, and no actual intelligence. You can ask all you want, but it’s not really much different than asking somebody at a bar. The rules require citing mainstream science in discussions, and AI does not limit itself to that (i.e. it makes stuff up)

GR makes specific predictions, and they have repeatedly been shown to be correct.

 

[tmdarkmatter]

Just now, Markus Hanke said:

Redshift measurements are not done by observing anything “getting smaller”,

I think you did not understand. I am saying that if redshift is not caused by expansion of the universe, we would have to use these other methods (again).

2 minutes ago, Markus Hanke said:

so local effects such as the ones you mentioned can be safely ignored on very large scales.

One question here: are these effects simply ignored because we cannot measure them or are we indeed able to measure them?

If we would be able to measure these local effects, why would we ignore them?

[Markus Hanke]

9 minutes ago, tmdarkmatter said:

 

I like to ask the AI about these topics because the AI has no prejudice:

 

Current AI’s are language models, they possess no real understanding of the subject, and as such their answers are quite often wrong or misleading. That is why they are not valid sources of scientific information.

12 minutes ago, tmdarkmatter said:

Circular relationship? Lol

So is Newtonian gravity - we measure forces because there is gravity, and there’s gravity because a force is exerted. So what? The model still works well within its specific domain, which is why we still learn it at school. But go outside of its domain, and it fails miserably.

5 minutes ago, tmdarkmatter said:

One question here: are these effects simply ignored because we cannot measure them or are we indeed able to measure them?

You yourself just quoted a paper that provides an example of some of these local effects being measured. But like I said, they are very small compared to the z~10 cosmological redshifts.

[tmdarkmatter]

19 minutes ago, Markus Hanke said:

so local effects such as the ones you mentioned can be safely ignored on very large scales.

If the solar system is moving around the center of the milky way at a speed of 222 km/s and the galaxy Andromeda is coming closer at a speed of 120 km/s, how can we say that the movement around the milky way should be safely ignored while the movement of Andromeda is very important?

Something is wrong here.

Are these effects being ignored on purpose to sustain the current model of the universe?

If course, if we cannot detect a redshift caused by movements within our galaxy, why should we suppose that movements of galaxies far away should be responsible for their redshift?

Edited November 14, 2023 by tmdarkmatter

[swansont]

2 hours ago, tmdarkmatter said:

If the solar system is moving around the center of the milky way at a speed of 222 km/s and the galaxy Andromeda is coming closer at a speed of 120 km/s, how can we say that the movement around the milky way should be safely ignored while the movement of Andromeda is very important?

Something is wrong here.

Are these effects being ignored on purpose to sustain the current model of the universe?

If course, if we cannot detect a redshift caused by movements within our galaxy, why should we suppose that movements of galaxies far away should be responsible for their redshift?

Moving 222 km/sec is (largely) tangential motion, while 120 km/sec wrt Andromeda is not.

I think the most prominent issue has has to be discerning what orbital motion is, why that’s not the same as linear motion and why it has nothing to with expansion, since you seem to be confused about this.

[tmdarkmatter]

26 minutes ago, swansont said:

Moving 222 km/sec is (largely) tangential motion, while 120 km/sec wrt Andromeda is not.

So because it is a tangential motion we are allowed to ignored it, that´s interesting. Because even in a tangential motion the linear speed can be between 0 and 1 according to the angle, multiplied by the 222 km/s, but that of course does not matter.

 

26 minutes ago, swansont said:

why it has nothing to with expansion, since you seem to be confused about this.

I have already explained many times how this is related to expansion, but of course only I should be confused.

So we are actually riding a carousel towards Andromeda but some smart and "not confused" guys prefer to interpret that as Andromeda beeing on a collision course with the milky way while the motion of the carousel of 222 km/s can definitely be ignored. Very nice, I love modern science! It all makes a lot of sense. I think that in about 80 million years, Andromeda will be redshifted when it is behind us, so the next civilization with telescopes will consider that Andromeda was always moving away from us. lol

[swansont]

21 minutes ago, tmdarkmatter said:

So because it is a tangential motion we are allowed to ignored it, that´s interesting. Because even in a tangential motion the linear speed can be between 0 and 1 according to the angle, multiplied by the 222 km/s, but that of course does not matter.

Orbital motion is not expansion. This is a pretty fundamental issue; motion constrained by being gravitationally bound systems is not expansion. Orbital motion is quite definitely from being gravitationally bound.

 

21 minutes ago, tmdarkmatter said:

I have already explained many times how this is related to expansion, but of course only I should be confused.

I’m sure you aren’t the only one.

21 minutes ago, tmdarkmatter said:

So we are actually riding a carousel towards Andromeda but some smart and "not confused" guys prefer to interpret that as Andromeda beeing on a collision course with the milky way while the motion of the carousel of 222 km/s can definitely be ignored.

Some people can do math and distinguish these two components of motion, and the effects that arise from it.

 

21 minutes ago, tmdarkmatter said:

Very nice, I love modern science! It all makes a lot of sense. I think that in about 80 million years, Andromeda will be redshifted when it is behind us, so the next civilization with telescopes will consider that Andromeda was always moving away from us. lol

Andromeda is part of the local group, and so is gravitationally bound. Also not subject to expansion.

In however many millions of years, anyone versed in the appropriate science will be able to figure out that Andromeda (or whatever is left of it) passed by/through us.

[tmdarkmatter]

19 minutes ago, swansont said:

Orbital motion is not expansion.

Why are you still mixing up this motion with expansion? My question was: why do we not detect/ignore the redshifting of near objects caused by the movements of our solar system around the center of the milky way?

Half of the sky should be more blueshifted and the other half should be more redshifted only because of this motion.

Lol, these "negative points" will not improve our understanding of the universe.

Edited November 14, 2023 by tmdarkmatter

[swansont]

1 hour ago, tmdarkmatter said:

Why are you still mixing up this motion with expansion?

You were talking about galactic redshift, which is due to expansion.

1 hour ago, tmdarkmatter said:

My question was: why do we not detect/ignore the redshifting of near objects caused by the movements of our solar system around the center of the milky way?

As I said, you do some math and separate the effects. If we know our velocity, we can subtract it. As has already been pointed out, it’s a small number with respect to distant galaxies 

 

1 hour ago, tmdarkmatter said:

Half of the sky should be more blueshifted and the other half should be more redshifted only because of this motion.

Again, one needs to do the math. What is the red- or blue shift for 300 km/sec?

z=?

 

[tmdarkmatter]

The point is that scientists are ignoring this completely.

1 hour ago, swansont said:

If we know our velocity

Do we know our velocity? lol

[swansont]

3 hours ago, tmdarkmatter said:

Do we know our velocity? lol

You appeared to cite it. Did you just make that number up?

Quote

The point is that scientists are ignoring this completely.

And we’re supposed to take your assertion as fact?

If you answered my question, or read what Markus posted, you’d see that such pedestrian speeds are small compared to recession values of distant galaxies. Ignoring it in certain calculations is completely reasonable, e.g. when it’s smaller than uncertainties in the result. If you only know z to one or two digits for z >1 , ignoring a speed with z ~ 0.01 is not a problem, if you understand how significant digits work.

[tmdarkmatter]

On 11/14/2023 at 11:42 PM, swansont said:

you’d see that such pedestrian speeds are small compared to recession values

If we can ignore these pedestrian speeds, shouldn't we also ignore the blueshift of Andromeda? This blueshift is way too low for us to take it into account.

All this drama of Andromeda hitting the milky way is just fake news, because the blueshift is just too low and is completely negligible.

[Bufofrog]

2 hours ago, tmdarkmatter said:

If we can ignore these pedestrian speeds, shouldn't we also ignore the blueshift of Andromeda? This blueshift is way too low for us to take it into account.

You can ignore it when you are trying determine the red shift of very distant galaxies.

2 hours ago, tmdarkmatter said:

All this drama of Andromeda hitting the milky way is just fake news, because the blueshift is just too low and is completely negligible.

The Andromeda galaxy is going to hit milky way, it isn't fake.  This stuff really seems to be confusing you, have you tried googling the topic to gain some more understanding?

[tmdarkmatter]

38 minutes ago, Bufofrog said:

The Andromeda galaxy is going to hit milky way, it isn't fake.  This stuff really seems to be confusing you, have you tried googling the topic to gain some more understanding?

Well, I guess that if the "pedestrian speeds" should be ignored, I think I can make a joke about ignoring the movements of Andromeda too, because we are moving much faster around the center of the galaxy than Andromeda is moving into our direction.

[Bufofrog]

1 hour ago, tmdarkmatter said:

Well, I guess that if the "pedestrian speeds" should be ignored, I think I can make a joke about ignoring the movements of Andromeda too

Great joke.

1 hour ago, tmdarkmatter said:

because we are moving much faster around the center of the galaxy than Andromeda is moving into our direction.

While that is true it has no relevance to much of anything except that the speeds are different.

[tmdarkmatter]

23 hours ago, Bufofrog said:

While that is true it has no relevance to much of anything except that the speeds are different.

So are scientists having in mind these "pedestrian speeds" when calculating the redshift of Andromeda or not?

[iNow]

When you track how fast you're driving in your car down the highway, do you account for the backpressure applied to your windshield from the wing flap of a mosquito? 

[Bufofrog]

3 hours ago, tmdarkmatter said:

So are scientists having in mind these "pedestrian speeds" when calculating the redshift of Andromeda or not?

Yes.

From Wiki about Andromeda–Milky Way collision:

Taking also into account the Sun's motion, Andromeda's tangential or sideways velocity with respect to the Milky Way was found to be much smaller than the speed of approach (consistent with zero given the uncertainty) and therefore it will eventually merge with the Milky Way in around 5 billion years.

Edited November 17, 2023 by Bufofrog