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The case for, and against, the still-unseen Planet 9

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Re: The case for, and against, the still-unseen Planet 9

#21

Post by alpaca128 »

m463 wrote: post #11
RupertEisenhart wrote: post #4

I love that this is still a topic-- along with 'is glass a fluid', this is one of the few questions I recall from childhood that turns out to still be relevant serious physics. (Re 'is glass a fluid', my condensed matter professor said something like 'if it is, it flows too slowly to observe significant movement in the lifetime of the universe'.)

Why does a mirror reverse left and right, but not up and down? and does it have something to do with us having two eyes?

Because a mirror doesn't reverse anything. The only reversed part is our perception because we compare it to how a person actually standing in front of us would look.

Re: The case for, and against, the still-unseen Planet 9

#22

Post by djbebs »

chriswarbo wrote: post #5
DukeBaset wrote: post #2

It's called Pluto and it's a planet - Jerry

I think your counting's off: if you want to count dwarfs then Ceres would be "Planet 5", in which case "Planet 9" would be Neptune most of the time, since only a small part of Pluto's orbit crosses inside Neptune's. Pluto's number would also depend on the current location of at least Quaoar, Haumea and Makemake, since I know their orbits cross inside Pluto's. Pluto may also swap numbers over time with others, like Se…

Pluto is an order of magnitude larger than Ceres, so its perfectly possible to define planet in such a way that pluto is a planet and ceres is not.

Re: The case for, and against, the still-unseen Planet 9

#23

Post by Ma8ee »

jerryluc wrote: post #12
m463 wrote: post #11

Earlier quoted context omitted.

Why does a mirror reverse left and right, but not up and down? and does it have something to do with us having two eyes?

Physics girl explains it well: https://m.youtube.com/watch?v=vBpxhfBlVLU

That was a really good explanation. In particular the part that we don’t flip left-right, but rather forward-backward and how she illustrated it with the glove.

Re: The case for, and against, the still-unseen Planet 9

#24

Post by seppel »

alpaca128 wrote: post #21
m463 wrote: post #11

Earlier quoted context omitted.

Why does a mirror reverse left and right, but not up and down? and does it have something to do with us having two eyes?

Because a mirror doesn't reverse anything. The only reversed part is our perception because we compare it to how a person actually standing in front of us would look.

> Because a mirror doesn't reverse anything.

Well, a mirror gives you a different picture than a webcam and a computer screen (unless the webcam software flips the picture along the x axis).

Now why is that, that the software needs to flip along the x axis? It is actually because a mirror mirrors around the the z axis, so it switches front and back.

Re: The case for, and against, the still-unseen Planet 9

#25

Post by cedilla »

seppel wrote: post #24
alpaca128 wrote: post #21

Earlier quoted context omitted.

Because a mirror doesn't reverse anything. The only reversed part is our perception because we compare it to how a person actually standing in front of us would look.

> Because a mirror doesn't reverse anything. Well, a mirror gives you a different picture than a webcam and a computer screen (unless the webcam software flips the picture along the x axis). Now why is that, that the software needs to flip along the x axis? It is actually because a mirror mirrors around the the z axis, so it switches front and back.

It's the webcam that is flipped.

Re: The case for, and against, the still-unseen Planet 9

#26

Post by bnralt »

chriswarbo wrote: post #5
DukeBaset wrote: post #2

It's called Pluto and it's a planet - Jerry

I think your counting's off: if you want to count dwarfs then Ceres would be "Planet 5", in which case "Planet 9" would be Neptune most of the time, since only a small part of Pluto's orbit crosses inside Neptune's. Pluto's number would also depend on the current location of at least Quaoar, Haumea and Makemake, since I know their orbits cross inside Pluto's. Pluto may also swap numbers over time with others, like Se…

> Dwarf planets seem to be lucrative business for those who sell wall posters of the solar system. I would hate having to learn all of their relative locations and interactions in school!

That seems to have been the main reason the majority in the IAU voted to make dwarf planets not considered actual planets. Can't really say I agree with the mindset - it overly simplifies our solar system, as well as making the rocky planets appear more similar to the gas giants than they actually are (a problem in a lot of images of the solar system as well).

It's funny to see the number of people who believe the definition was just following scientific facts, when the vote came down to personal preferences over nomenclature. It's one of the more common examples you run into where modern day scientism has trouble distinguishing what is and what isn't science.

Re: The case for, and against, the still-unseen Planet 9

#27

Post by mjw1007 »

aaron695 wrote: post #18

This article doesn't give either the for or the against, as we currently stand. I'm not really sure how it's debatable, either their evidence was correct or not. Surely a respectable third person can look and tell us? The mathematics has been out for 6 weeks. > “It is important to note that our work does not explicitly rule out Planet X/Planet 9" I find this annoying. If it disproves their evidence, which I assume wa…

The linked blog post at http://findplanetnine.blogspot.com/2021/02/is-planet-nine-fi... has some more detail, though it's from the proponents of the theory rather than someone trying to be neutral.

It looks like there are two things going on:

- With the current set of observations, the evidence for clustering is fairly strong, but well short of strong enough that it can't just be chance.

- The new survey was including one data point (which doesn't fit in the 'cluster') that Mike Brown doesn't think counts [1]. With the numbers involved, it seems to me that one additional data point is likely to be making a big difference.

[1] « there is one additional object that Napier et al. include that was never reported to the Minor Planet Center; we restrict our analysis to objects whose detection history we can track; that one unreported object is down in the lower left of the lefthand plot »

Re: The case for, and against, the still-unseen Planet 9

#28

Post by JNRowe »

atoav wrote: post #17
tjpnz wrote: post #10

The theory which most fascinates me is that it's not a planet at all, but a primordial black hole with a diameter of ~5cm.

I love the fact that the paper which introduced that theory had a 1:1 illustration of that black hole in it.

"Exact scale (1:1) illustration of a 5M⊕ PBH."¹

¹ https://arxiv.org/abs/1909.11090

Re: The case for, and against, the still-unseen Planet 9

#29

Post by scatters »

m463 wrote: post #11
RupertEisenhart wrote: post #4

I love that this is still a topic-- along with 'is glass a fluid', this is one of the few questions I recall from childhood that turns out to still be relevant serious physics. (Re 'is glass a fluid', my condensed matter professor said something like 'if it is, it flows too slowly to observe significant movement in the lifetime of the universe'.)

Why does a mirror reverse left and right, but not up and down? and does it have something to do with us having two eyes?

A mirror reverses front and back. Because we are (more or less) horizontally symmetrical, we reduce the discrepancy by rotating the image around a vertical axis, resulting in a left-right reversal. If we were vertically symmetrical we would see mirrors as reversing up and down; if we were front-back symmetrical (a pushmi-pullyu) we would see mirrors as they are.

Re: The case for, and against, the still-unseen Planet 9

#30

Post by aaron695 »

mjw1007 wrote: post #27
aaron695 wrote: post #18

This article doesn't give either the for or the against, as we currently stand. I'm not really sure how it's debatable, either their evidence was correct or not. Surely a respectable third person can look and tell us? The mathematics has been out for 6 weeks. > “It is important to note that our work does not explicitly rule out Planet X/Planet 9" I find this annoying. If it disproves their evidence, which I assume wa…

The linked blog post at http://findplanetnine.blogspot.com/2021/02/is-planet-nine-fi... has some more detail, though it's from the proponents of the theory rather than someone trying to be neutral. It looks like there are two things going on: - With the current set of observations, the evidence for clustering is fairly strong, but well short of strong enough that it can't just be chance. - The new survey was includin…

Kevin Napier (First of the 50 authors on the against paper) talks here - https://www.youtube.com/watch?v=e-6OrCJ9ZEU (32 mins)

It addresses the above a bit and its interesting in its own right talking about Kuiper belt stuff.

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