#26122: Ian Musgrave — 05/26  at  07:34 AM
Alright, why isn't my gravitar showing? I will use this opportunity to mention the Bad Asytonomers musings on why we should call pseudoscientists anti-scientists http://www.badastronomy.com/bablog/?p=63

Orac is convinced, and I think I am too.

Oh yes, and I'm a sucker for Saturns rings
http://antwrp.gsfc.nasa.gov/apod/ap050525.html

#26123: Josh Friess — 05/26  at  07:47 AM
"You can do physics, but if you refuse to recognize that you are in a non-inertial frame of reference, you're going to have a complicated system."

Very true.

You'll note that in post #30 I said: "In fact, not only can I choose the origin, but I can also choose to work in a coordinate system that is "rotating" or moving linearly. The expense for doing so is sometimes to add additional "fictitious forces" to the problem, such as the centrifugal and coriolis forces....Often there is a choice that makes your calculations simple, and any other choice makes them quite difficult."

At no point have I said that all coordinate frames are inertial.

Ian, I believe you have once again failed to take into account these kinds of fictitious forces that arise in non-inertial frames in your statements.

#26126: PZ Myers — 05/26  at  07:55 AM
It's showing up now. My, you look cranky -- is it because you have the Sydney Opera House jammed into your head and dribbling out your ears?

I like the "anti-science" term, too.

#26133: — 05/26  at  08:22 AM
Ian, your avatar is showing fine. First I thought I was seeing Facundo Quiroga, a noted Argentine caudillo de montoneros but he never visited Sidney. BTW, Josh latest post seems to be answering Virge's comment, not yours.

I hope we are in agreement that Biblical astronomy is unfeasible, if not, physics teachers too may be requested to "teach the controversy". On second thought, they still may be asked to do so.

#26144: Josh Friess — 05/26  at  09:11 AM
"I hope we are in agreement that Biblical astronomy is unfeasible."

If by "Biblical astronomy" you mean Geocentrism, then yes, of course.

#26153: — 05/26  at  11:11 AM
Josh, may "Biblical astronomy" have a different meaning? Does your observation suggest that "Biblical astronomy" may be workable within the framework of contemporary astronomy and physics?

#26198: Ian Musgrave — 05/26  at  04:07 PM

Ian, I believe you have once again failed to take into account these kinds of fictitious forces that arise in non-inertial frames in your statements.

No, I just can't see for the life of me what kind of ficticious force would generate, for example, stellar paralax. Centrifugal and coriolis forces can't possibly do it, and I am at a loss to think of any other force that will generate stellar paralax without doing some serious violence to physics. And that's just one thing, how do you account for retrogrde motion with these ficticous forces at the same time?

So I would be grateful for an explanation of stellar paralax (that generates the distance dependent paralax we see for different stars) at least in an Earth centered solar syste (with the other planets orbiting the Sun)

#26201: Ian Musgrave — 05/26  at  04:16 PM
G'Day All,

The gravitar is showing up now as I have removed the obvious spam defeating modification from my email address on my postings here (DUH).

PZ, I am now an offical Grumpy Old Man (http://www.abc.net.au/tv/guide/netw/200504/programs/ZY7681A001D12042005T200000.htm)
I bet I can do a better job of being grumpy than Rick Wakeman. My postgrad students are getting together to make me a GOM badge.

You would look grumpy too if you had just sat through a day of student talks where the majority of students spent more time on flash powerpoint animations than on understnading the science in their presentations (or presenting it logically, or spell- checking). Powerpoint is evil
http://www.wired.com/wired/archive/11.09/ppt2.html

#26203: PZ Myers — 05/26  at  04:41 PM
I agree. I haven't used PowerPoint in about 5 years now.

This must be another of those things we old men are grumpy about. But it is a righteous grumpiness.

#26209: Virge — 05/26  at  05:38 PM
I'm still keeping my foot in the door with the POFs (Pedantic Old Farts) but I chuckle too much to be a GOM.

#26248: Josh Friess — 05/26  at  10:02 PM
Ian,

When moving to a fixed-Earth coordinate system, there are two transformations -- the first is to put the Earth at the origin of the coordinate system, and the 2nd is to make the Earth stop rotating in your choice of reference frame. By the first transformation, distant stars will move in small circles depending on the position of the sun (i.e., parallax).

I really don't have time to respond on this thread any more. So if you have any other questions you'll have to figure them out for yourself. But there's no point in answering bad science (Geocentrism) with more bad science (the claim that one can not do physics in an Earth-centered reference frame).

Josh

#26255: — 05/26  at  11:57 PM
I use projector and transparencies. Powerpoint is more trouble than it is worth.

I am amazed at the end of this thread. My questions to Josh are left unanswered, suggesting he is in the opinion that the Bible is literally correct or may be explained through mental acrobatics. Hasta la vista.

#26259: Virge — 05/27  at  01:28 AM
No jaimito, I don't think Josh is doing anything to support biblical assertions.

He already agrees that geocentrism is unfeasible, but by sticking to the "you can do physics in a non-inertial frame", he's playing down the levels of complication. It's more that just applying a coordinate transform and adding centrifugal and coriolis fictitious forces. That only deals with local observations on earth.

To deal with stellar parallax from a fixed earth, every star needs to have a different value of a fictitious force to make it move in a small circle with a period of exactly 1 earth year (and another fictitious force to add tiny earth-daily circles if you could measure it).

It's not "bad science" to reject the idea of introducing a couple of special forces for each and every individual star. It's not "bad science" to reject a model that prevents you explaining observations of relativistic effects.

"So if you have any other questions you'll have to figure them out for yourself" could perhaps be read as, "Ian, your questions are too hard, so I'll pretend the answers are simple for persons sufficiently skilled in the art."

For persons with insufficient skill (such as myself) a pointer to a website that shows simple answers to Ian's questions would be useful and far more convincing.

#26260: Virge — 05/27  at  01:33 AM
Ignore that bit about "tiny earth-daily circles". I'm not used to thinking geocentrically. They are, of course, huge earth-daily circles and easily measured.

(Must preview posts for more than just grammar.)

#26272: Josh Friess — 05/27  at  04:31 AM
Virge, Post #61 contains the answer to your argument in #63 -- please re-read. And I've already referenced a couple of books you can find. Try google if you want a web reference.

#26279: Ian Musgrave — 05/27  at  06:06 AM

Josh wrote: Virge, Post #61 contains the answer to your argument in #63

No, it's not, its just a declarative statement.

.. the first is to put the Earth at the origin of the coordinate system, .... By the first transformation, distant stars will move in small circles depending on the position of the sun (i.e., parallax).

Why? Just saying it does doesn't explain it. If the earth is the centre of a co-ordinate system, then the "fixed" stars shouldn't show paralax, because the earth isn't moving. If you wobble the fixed stars to simulate paralax, you break physics, because the lwas of gravity won't allow them to move like that.

As a simple thought experiment, imagine a small mass approaching a much larger mass, gravity causes the small mass's trajectory to be defleted under the influence of gravity. Now you can re-define the co-ordinate system so that the large mass is deflected by the small mass. But if you do this you break gravity, small masses won't deflect large masses in this way (of course, the large mass is slightly moved by the small mass, but this is insignficant in this case - even if you run the thought experiment as a large mass approaching a small mass it's still the small mass that gets deflected under the laws of gravity).

Now, you are either doing mathematical jiggery pokery which has no physical meaning, or you are breaking physics. Either way, Charlie Wagner is completely wrong when he says "WE choose the sun as the center of the solar system because it is aesthetically pleasing"

(also, anyone at Alpha Centauri (with a REALLY good occulting scope) looking at the Sun will see Earth rotating around the Sun, as will anyone at Tau Ceti, or Barnards star or Upsioln Andromedae. The same arguments aply to extrasolar planets as well. If an extrasolar plabet is at the centre of ur's co-ordinate system, how come we see it orbiting its star? We don't say Upsiolon andromedae D orbits Upsilon Andromedae because it is astheticlly pleasing, but becuase that is what we observe (or the galilaen moons around Jupiter etc.)

#26298: Virge — 05/27  at  10:20 AM
Josh Friess wrote:

Virge, Post #61 contains the answer to your argument in #63 -- please re-read. And I've already referenced a couple of books you can find. Try google if you want a web reference.

Ok, I did my refresher on centrifugal and coriolis "forces". I'll take back my complaint about special values of forces for each star, since a stationary-earth model can be expressed with position and velocity-dependent accelerations rather than forces.

Considering the spiral path taken by light in travelling from Betelgeuse to Earth was instructive for understanding the apparent speed problem for distant stars. The fictitious coriolis force means that light doesn't travel in straight lines and the linear distance to a star is not the distance light travels to reach earth from that star.

Thinking about the universe as a rolled up newspaper is a pain in the wetware. Probably best left until after a few drinks.


Charlie's initial statement:
There's absolutely no logical reason why the earth could not be considered to be "stationary"
only appears to be correct if you take his hypothetical situation in which there is nothing but empty space. (And if we did have an earth in a completely empty universe for testing, I'd still try swinging a pendulum just to check that assertion.)

Since we do not have an empty universe, Charlie's claim doesn't hold. In this real universe, Einstein's Special Relativity presents a very logical reason for making a distinction between inertial and non-inertial frames of reference.

#26304: Josh Friess — 05/27  at  10:42 AM
Take a piece of paper, put a quarter on it. The rim of the quarter represents the orbit of the earth around the center of the quarter, i.e., the sun. Now draw a dot somewhere far away from the quarter. This is a star.

Take a pen, trace repeatedly around the quarter. This represents the movement of the earth in a heliocentric coordinate system. Note that the star doesn't move.

Now, cut out the circle that you traced around the quarter, so there's a hole in the paper. Put your pen in some fixed position on the table, and now move the paper in a circular fashion so that the edge of the hole is always touching the pen. This represents the movement of other "stuff" in a geocentric coordinate system. Note how the star, in this coordinate system, moves in a circular fashion, and that the apparent position of the star changes from the perspective of the fixed-earth observer, i.e., parallax.

If you want to be really fancy, you can spin the paper (i.e., revolve the Earth on its axis) as you move the paper in circles (i.e., orbit the earth around the sun, or sun around the earth, as you prefer).

#26322: — 05/27  at  12:04 PM
I haven't posted on this thread for a few days, but I have been reading the responses. I still think everybody is talking past each other. Just to state my own views again:
1) There exists a frame of reference in which the Earth is non-moving and non-rotating.
2) One can do physics in such a frame of reference
3) It is actually a pretty sensible frame of reference in which to do physics (or just navigate your way into work in the mornings) provided one is only interested in things mostly confined to the Earth's surface.
4) It becomes increasingly messy as one ventures beyond that. If one is interested in explaining phenomena beyond the solar system, such a frame of reference rapidly becomes intolerable
5) None of this has anything whatever to do with the bovine digestive biomass at http://www.fixedearth.com

I have been back and looked at some of the other pages at that site, although I can only read it in small doses because it makes my head hurt. If you haven't taken the time to wander around the voluminous nonsense, this particular sample (apparently taken from the book which gets plugged in just about every paragraph of the rest of the site) should illustrate:

"This "Universal Law of Gravitation" is taught and believed by one and all but is, nevertheless, an absolutely insane concept which violates and contradicts its essential magnetic principle every second of every day, year in and year out."

"Indeed, the undeniable reality is that the moon regularly varies its distance from the Earth by over 31,000 miles! When it comes closer and closer it gets in the stronger and stronger pull of Earth’s gravity. How can it then resist that pull and start going against that attraction? Contrariwise, as it goes out to the apogee and is moment by moment breaking loose from Earth’s gravitational pull at tremendous speed, how can it stop the outward movement and start back??"

http://www.fixedearth.com/tides.htm

this stuff is just painful to read...

Regards
Duncan

#26324: charlie wagner — 05/27  at  12:07 PM
Josh is absolutely correct. Go back and re-read what I said:

"In an earth-centered universe, the sun, planets and stars are not revolving around the earth. They are still moving relative to *each other*, just as they did before. The only thing we've changed is their position relative to spacetime. And that doesn't matter because an object in spacetime has no way of determing "where it is". The laws of Physics don't even enter into the picture because it has nothing at all to do with defining the bodies in the universe with respect to each other. That part is not changing. We're only defining one particular point as the "center" instead of a different point. It's just conceptual."

#26335: Josh Friess — 05/27  at  12:30 PM
Duncan -- I agree with everything you said. I'm glad we're on the same page now.

Charlie -- Thanks for the support.

Josh

#26369: — 05/27  at  04:03 PM

Duncan said "It is actually a pretty sensible frame of reference in which to do physics (or just navigate your way into work in the mornings) provided one is only interested in things mostly confined to the Earth's surface".

In the same vein, a map based on the Flat Earth hypothesis is pretty sensible to navigate my way into work. In fact, I do use such a map of the city, which is not even a Mercator projection, to find the best route. It works very well, provided you are interested in the streets of the city and do not rise your eyes to the horizon. Then the system "becomes increasingly messy". On the beach, for example, the map would not help to explain why you see first the top of the mast of that approaching ship.

In other words, Biblical astronomy is sensible if you ignore all we have learned about the universe in the last 2,500 years. If you try to harmonize the Bible with facts known even to the Greeks, it starts to become messy. So we leave it there.

Duncan is too soft on that FlatEarth site. I started to get sick from Both the Helio and the Big Bang Models represent the fulfillment of a "creation scenario" of Kabbalic Judaism masquerading as "science". At least, Creationists dont accuse us of having invented evolution for our sinister purposes.

#26382: — 05/27  at  05:38 PM
jaimito,
completely agree with your first two paragraphs. Not so sure about being "too soft" on the author, though; I didn't think I exactly said anything positive

I see on those pages crankiness reminiscent of the nuttier end of the spectrum of sci.astro crackpots, for sure. Perception of a giagantic conspiracy including everybody who has ever lived and who ever said anything that disagrees with them is a common thread. I've had, erm, "discussions" with such people at other forums (specifically Bad Astronomy and Godlike Productions), and in my experience any attempt to point out the ridiculousness of that kind of conspiracy is futile. Anybody who buys into it is already beyond reason.

The only thing open for discussion are those which submit to rational analysis. That's why I prefer to stick to those things exclusively.

Regards
Duncan

#26631: Josh Friess — 05/30  at  04:01 PM
Ian, Virge, I take it from your lack of response that my explanation with the paper and the quarter has sufficed for you?

#26635: Virge — 05/30  at  04:50 PM
I'd already worked through my misunderstandings in comment #67, thanks Josh. I guess my comment slipped in between when you'd viewed the thread and when you'd posted #68.