Cosmologists intrigued by signs the universe might stop expanding; influence of dark energy may be weakening

[Hans Blaster]

Fact: stellar parallax values are either positive, negative or zero.

Fact: the Bayesian experts that “clean-up” the observed data are biased towards their preferred model (the model they philosophically believe in)

It might help to learn about how the parallaxes from Gaia are actually calculated and what they mean.

This review covers how to use Gaia parallaxes, particularly section 3 discusses negative parallaxes.

Gaia Data Release 2 - Using Gaia parallaxes | Astronomy & Astrophysics (A&A)

The model includes two primary components -- the linear motion of the object across the sky (the proper motion as it is known) and the back-and-forth wiggle relative to that moving point (the parallax). Figure 2 from that paper illustrates how noisy simulated data generated from a modeled star with positive parallax (which all ideal stars must have) results in *negative* parallax when processed through the data analysis algorithms.

Gaia Data Release 2 - Using Gaia parallaxes | Astronomy & Astrophysics (A&A)

In other words:

NEGATIVE PARALLAX IS A CONSEQUENCE OF NOISY DATA

Other parts of the paper warn users of Gaia data not to toss out "negative parallax" objects because that would bias the sample towards brighter stars (brighter stars have less noise), closer stars (close stars have proper motions and parallaxes that larger and therefore easier to detect) and most insidious of all, toward the equally noisy distant objects that have small parallaxes that are randomly larger due to noise.

 

[sjastro]

Now we're talking my language -- cartoons!

Your model

View attachment 364368

geocentric model

View attachment 364369


enough said regarding original challenge. I've had enough on the topic of parallax. I'm fascinated with what I'm learning about quasars though. Again, thanks for the lead.

This is pure comedy since Shack is unable to illustrate geometrically how negative parallax as a real value works so you decide to alter my images only to prove you don't understand what parallax is and the altered images are not examples of negative parallax.

Here is an accurate way of doctoring an image to illustrate astronomical parallax by taking into consideration the movement of the foreground star in opposite directions.

The parallax p is the angle between the hypotenuse and the adjacent sides of the right angle triangle formed and it doesn't matter whether the foreground star is drifting "up" or "down", the right angle triangles are equivalent. It makes a nonsense of Shack's argument negative parallax is the result of star drift in an opposite direction.
Furthermore anyone who has a high school knowledge of geometry would know the parallax angle can never be negative as the interior angles of triangle (in Euclidean space) always add up to 180⁰.

As I asked in my previous post do you also believe the Earth is flat and surrounded by a firmament?

 

[awstar]

This is pure comedy since Shack is unable to illustrate geometrically how negative parallax as a real value works so you decide to alter my images only to prove you don't understand what parallax is and the altered images are not examples of negative parallax.

Here is an accurate way of doctoring an image to illustrate astronomical parallax by taking into consideration the movement of the foreground star in opposite directions.

View attachment 364391​

The parallax p is the angle between the hypotenuse and the adjacent sides of the right angle triangle formed and it doesn't matter whether the foreground star is drifting "up" or "down", the right angle triangles are equivalent. It makes a nonsense of Shack's argument negative parallax is the result of star drift in an opposite direction.
Furthermore anyone who has a high school knowledge of geometry would know the parallax angle can never be negative as the interior angles of triangle (in Euclidean space) always add up to 180⁰.

As I asked in my previous post do you also believe the Earth is flat and surrounded by a firmament?

OK — I am now admitting I don’t understand your diagram at all. In my cartoon, I was trying to show how parallax is the change in the angle between a near star and a far star after two different readings. If there were no changes in their relative position — no parallax. if any changes at all occur in their relative positions — parallax exists and the angle between the new position and old position is the amount of parallax. The sun isn’t involved at all, only time changes. (I understand that aberration and proper motion have to be accounted for, but let’s simplify the cartoon to just parallax.)

Please explain where my thinking is in error. Thanks.

 

[sjastro]

OK — I am now admitting I don’t understand your diagram at all. In my cartoon, I was trying to show how parallax is the change in the angle between a near star and a far star after two different readings. If there were no changes in their relative position — no parallax. if any changes at all occur in their relative positions — parallax exists and the angle between the new position and old position is the amount of parallax. The sun isn’t involved at all, only time changes. (I understand that aberration and proper motion have to be accounted for, but let’s simplify the cartoon to just parallax.)

Please explain where my thinking is in error. Thanks.

Parallax is calculated using triangulation where the baseline of the triangle is the straight line distance between two locations.
The ancient Greeks were able to measure the moon's parallax as it's distance is short enough for the baseline to be from two locations on the Earth's surface.
For distant objects like stars the baseline is 300 million kilometres long which is the Earth's position in its orbit six months apart.
A stationary Earth will not provide long baselines for the parallaxes of stars to be measured.

My diagram shows foreground star movement for two separate six month intervals, June to December and December to June. The star moves in opposite directions for the two intervals but the right angle triangles are equivalent as are the parallaxes for each interval.
It serves to illustrate Shack's idea that a negative parallax occurs when stars move in opposite directions is comprehensively wrong.

 

[sjastro]

To expand further on my previous post on how the length of the baseline effects the parallax angle.

b is the diameter of the Earth's orbit and is approximately 300 million kilometres or 2 AU where the AU is the Earth-Sun distance.

Without going into the mathematics which can be derived using the above diagram the parallax p in arc seconds is given the the formula;

p = 1/d

d is in parsecs (pc) where a parsec is defined as the distance using a 1 AU baseline results in a star subtending a parallax angle of 1 arc second.

As an exercise let’s consider a star 100 pc away what is the parallax p if the baseline was (1) 1 AU and (2) the Earths diameter.
Case (1) p = 1 AU/100 = 0.01 arc second.
Case (2) Earths diameter ≈ 1.2742 x 10⁴ km, 1 AU = 1.496 x 10⁸ km and the baseline in terms of AU is 1.2742 x 10⁴/ 1.496 x 10⁸ ≈ 8.52 x 10⁻⁵ AU.
p = 8.52 x 10⁻⁵ AU/100 = 8.52 x 10⁻⁷ (or 0.85μ arc second.)
0.85μ arc second is well beyond observational limits, Gaia can measure down to ~ 20μ arcsecond.

Interestingly if one used Proxima Centauri which is 1.3 pc distant and the Earth’s diameter the parallax p ~ 65.5 arc second should theoretically be within range for earth based telescopes but the Earth’s rotation on its axis makes this impossible as the baseline's orientation changes with time which introduces false positional shifts.
The bottom line is parallax measurements are achieved using large baselines which can only be accomplished by using the Earth’s orbit.

 

[awstar]

To expand further on my previous post on how the length of the baseline effects the parallax angle.

View attachment 364488​

b is the diameter of the Earth's orbit and is approximately 300 million kilometres or 2 AU where the AU is the Earth-Sun distance.

Without going into the mathematics which can be derived using the above diagram the parallax p in arc seconds is given the the formula;

p = 1/d

d is in parsecs (pc) where a parsec is defined as the distance using a 1 AU baseline results in a star subtending a parallax angle of 1 arc second.

As an exercise let’s consider a star 100 pc away what is the parallax p if the baseline was (1) 1 AU and (2) the Earths diameter.
Case (1) p = 1 AU/100 = 0.01 arc second.
Case (2) Earths diameter ≈ 1.2742 x 10⁴ km, 1 AU = 1.496 x 10⁸ km and the baseline in terms of AU is 1.2742 x 10⁴/ 1.496 x 10⁸ ≈ 8.52 x 10⁻⁵ AU.
p = 8.52 x 10⁻⁵ AU/100 = 8.52 x 10⁻⁷ (or 0.85μ arc second.)
0.85μ arc second is well beyond observational limits, Gaia can measure down to ~ 20μ arcsecond.

Interestingly if one used Proxima Centauri which is 1.3 pc distant and the Earth’s diameter the parallax p ~ 65.5 arc second should theoretically be within range for earth based telescopes but the Earth’s rotation on its axis makes this impossible as the baseline's orientation changes with time which introduces false positional shifts.
The bottom line is parallax measurements are achieved using large baselines which can only be accomplished by using the Earth’s orbit.

I understand what you are saying more accurately now. I used your last diagram as a basis and added the parts that I was hung up about so that I could see both perspectives at once. But in the end we’re still talking about the same angle p.



This cartoon wasn’t intended to prove anything, I found it helpful for me to see what you were saying better. I added the celestial sphere around the earth so I could visualize what the right ascension and declination values were doing over time. And I added the equivalent p angles between the near star and the distant fixed point, which is where they live in my mind.





Regarding your comment “the baseline's orientation changes with time which introduces false positional shifts” I totally understand what you are saying. But I’m not ready to argue that perhaps they are true shifts in the geocentric frame. I’m going to take a rest now. Maybe read all the Bible verses that say the earth is fixed, to quiet my mind from all the stress I’ve place on it in the past few days

 

[sjastro]

In a previous post I mentioned relative and absolute frames of references regarding Hoyle’s comments, in this post it is about inertial versus rotating frames of reference.

A scientific experiment which refutes the Earth is stationary but instead spinning around a rotational axis is the Foucault pendulum.
In a grandfather clock the pendulum swings in a fixed a plane, a Foucault pendulum can swing in any vertical plane.
The Foucault pendulum remains in a fixed vertical frame relative to the stars which are in an inertial non accelerating frame, however since the Earth is spinning an observer on Earth will note the vertical plane in which the Foucault pendulum is swinging is rotating. This is the well known Coriolis effect which is a fictitious force and governs weather patterns such as the formation of hurricanes.

A Foucault pendulum at the North and South poles will take 24 hrs for the vertical plane to rotate 360 degrees but in opposite directions, the closer the pendulum is to the equator the longer the rotation period and at the equator the pendulum does not rotate.
Here is a video which goes further into the Foucault pendulum.

 

[Ophiolite]

A scientific experiment which refutes the Earth is stationary but instead spinning around a rotational axis is the Foucault pendulum

I delighted in watching the Foucalt pendulum at the Museum of Natural History in Houston. "Dominoes" were arranged in a circle around its centre of rotation so periodically one would be knocked over. It was quite entrancing to watch and ponder its significance.
I know I've also seen the one in the Science Museum London, but that one I cannot picture in my mind. Perhaps there are no "dominoes" to knock over.
If you haven't seen one, they are worth seeking out*. There are a lot set up around the planet. This is probably not an exhaustive list: List of Foucault pendulums - Wikipedia.

*Or, if you have large house with high ceilings, or a barn, you try making one.

 

[RileyG]

Yup.

I knew the universe was going to stop expanding since I was a kid.

I've heard about that, too.

 

[sjastro]

I delighted in watching the Foucalt pendulum at the Museum of Natural History in Houston. "Dominoes" were arranged in a circle around its centre of rotation so periodically one would be knocked over. It was quite entrancing to watch and ponder its significance.
I know I've also seen the one in the Science Museum London, but that one I cannot picture in my mind. Perhaps there are no "dominoes" to knock over.
If you haven't seen one, they are worth seeking out*. There are a lot set up around the planet. This is probably not an exhaustive list: List of Foucault pendulums - Wikipedia.

*Or, if you have large house with high ceilings, or a barn, you try making one.

Foucault pendulums are sold on eBay but I doubt the one illustrated would be terribly effective as the wire is not long enough and the bob seems to in contact with sand.

​

A myth should be dispelled Foucault pendulums do not prove toilets in the southern hemisphere flush in the counterclockwise direction and clockwise in the northern hemisphere.

 

[linux.poet]

MOD HAT ON​

This thread has had a cleanup to remove off topic posts that disparage science.​

From the forum Statement of Purpose for Physical & Life Sciences:
​

Do not flame other views. Christianity cannot be called a myth, and science cannot be called a religion or made up. Threads started, or responses made, to simply disparage science will be considered off topic to the forum.​

This thread is NOT about whether science has validity, it is about the cosmological expansion of the universe and the evidence that it may be slowing down. Please leave those of us who believe science has value to enjoy the science subforum in peace.

Let's get back on topic.​

MOD HAT OFF​

 

[linux.poet]

MOD HAT ON​

This thread is closed for moderation review.​

That is enough disrespecting SoPs, disregarding Mod Hats, and disruptive behavior for one day.​

MOD HAT OFF​

 

[linux.poet]

MOD HAT ON​

This thread has had more cleanup and is being reopened.​

Problem solved. Whew.​

MOD HAT OFF​

 

[AV1611VET]

This thread has had more cleanup and is being reopened.

We did kinda go all over the spectrum here, didn't we?

 

[sjastro]

Here is a video from Dr Becky that dark energy may not be Einstein's cosmological constant given the DESI data.
The subject matter starts from the 19 min 30 sec mark of the video.