Significant figures

Talk about anything but keep it polite and reasonably clean.
User avatar
jdaw1
Taylor 1900
Posts: 19687
Joined: 15:03 Thu 21 Jun 2007
Location: London
Contact:

Significant figures

Post by jdaw1 » 21:12 Fri 17 Jul 2015

Split from another form of drivel.

Glenn E. wrote:convinced the praticioners of certain religions that the Earth is, in fact, more than 6000 years old.
Traditionally dated to 4004 BC (see, amongst many others, AnswersInGenesis.org). As we’re now in 2015 AD, they accept almost two decades more than 6000 years. QED.

Glenn E.
Quinta do Vesuvio 1994
Posts: 3339
Joined: 22:27 Wed 09 Jul 2008
Location: Seattle, WA, USA

Re: A reason to get up early

Post by Glenn E. » 22:38 Sun 19 Jul 2015

jdaw1 wrote:
Glenn E. wrote:convinced the praticioners of certain religions that the Earth is, in fact, more than 6000 years old.
Traditionally dated to 4004 BC (see, amongst many others, AnswersInGenesis.org). As we’re now in 2015 AD, they accept almost two decades more than 6000 years. QED.
Too many significant digits. I used one, you get one. Your decades are lost as rounding errors.
Glenn Elliott

User avatar
jdaw1
Taylor 1900
Posts: 19687
Joined: 15:03 Thu 21 Jun 2007
Location: London
Contact:

Re: A reason to get up early

Post by jdaw1 » 00:04 Mon 20 Jul 2015

Glenn E. wrote:
jdaw1 wrote:
Glenn E. wrote:convinced the praticioners of certain religions that the Earth is, in fact, more than 6000 years old.
Traditionally dated to 4004 BC (see, amongst many others, AnswersInGenesis.org). As we’re now in 2015 AD, they accept almost two decades more than 6000 years. QED.
Too many significant digits. I used one, you get one. Your decades are lost as rounding errors.
Oh, you meant six millennia. In which case, very fair, even if slightly confused by you writing “6000 years”. Which, silly me, I took to mean 6000 years.

Glenn E.
Quinta do Vesuvio 1994
Posts: 3339
Joined: 22:27 Wed 09 Jul 2008
Location: Seattle, WA, USA

Re: A reason to get up early

Post by Glenn E. » 00:47 Mon 20 Jul 2015

jdaw1 wrote:
Glenn E. wrote:
jdaw1 wrote:
Glenn E. wrote:convinced the praticioners of certain religions that the Earth is, in fact, more than 6000 years old.
Traditionally dated to 4004 BC (see, amongst many others, AnswersInGenesis.org). As we’re now in 2015 AD, they accept almost two decades more than 6000 years. QED.
Too many significant digits. I used one, you get one. Your decades are lost as rounding errors.
Oh, you meant six millennia. In which case, very fair, even if slightly confused by you writing “6000 years”. Which, silly me, I took to mean 6000 years.
No, I meant 6000 years. Not 6000.0 years.

Perhaps you do it differently in the UK, but here in 'Murica trailing zeros are not considered significant unless followed by a decimal point.
Glenn Elliott

User avatar
jdaw1
Taylor 1900
Posts: 19687
Joined: 15:03 Thu 21 Jun 2007
Location: London
Contact:

Re: A reason to get up early

Post by jdaw1 » 10:08 Mon 20 Jul 2015

Glenn E. wrote:Perhaps you do it differently in the UK, but here in 'Murica trailing zeros are not considered significant unless followed by a decimal point.
Here on ThePortForum, if I sell you 600 bottles of Fonseca 1970 and deliver only 590, grumbling would be expected. Likewise with dates: offering for sale a 1980 but delivering a 1978 would also cause unhappiness.

(Should this conversation be split? Or just ended? Or both?)

PhilW
Taylor Quinta de Vargellas 1987
Posts: 2469
Joined: 14:22 Wed 15 Dec 2010
Location: Near Cambridge, UK

Re: A reason to get up early

Post by PhilW » 14:27 Mon 20 Jul 2015

Glenn E. wrote:Perhaps you do it differently in the UK, but here in 'Murica trailing zeros are not considered significant unless followed by a decimal point.
Entirely correct, BUT you have to state how many significant digits are present, which you did not, otherwise all digits are assumed to be significant.
jdaw1 wrote:Here on ThePortForum, if I sell you 600 bottles of Fonseca 1970 and deliver only 590, grumbling would be expected.
Please do. Dependent on the price there could be no grumbling at all, even if you are 100 bottles short - though a diatribe on numeracy would be highly likely.

Glenn E.
Quinta do Vesuvio 1994
Posts: 3339
Joined: 22:27 Wed 09 Jul 2008
Location: Seattle, WA, USA

Re: A reason to get up early

Post by Glenn E. » 17:08 Mon 20 Jul 2015

PhilW wrote:
Glenn E. wrote:Perhaps you do it differently in the UK, but here in 'Murica trailing zeros are not considered significant unless followed by a decimal point.
Entirely correct, BUT you have to state how many significant digits are present, which you did not, otherwise all digits are assumed to be significant.
Unless and until pedantry kicks in. :wink:

A neutral 3rd party expert witness has commented, so I withdraw. In the future jdaw1 may interpret my use of "planet" in reference to Pluto has a shorter and easier to type abbreviated form of "dwarf planet".
Glenn Elliott

User avatar
jdaw1
Taylor 1900
Posts: 19687
Joined: 15:03 Thu 21 Jun 2007
Location: London
Contact:

Re: Significant figures

Post by jdaw1 » 18:53 Mon 20 Jul 2015

Glenn E. wrote:In the future jdaw1 may interpret my use of "planet" in reference to Pluto has a shorter and easier to type abbreviated form of "dwarf planet".
Now this off-topic drivel has been split from the topic from which it was off (aside to the aside of the aside: I’m loving the prepositional torture), we can do the Pluto-is-Pluto-isn’t rant. I’ll show my cards: the Stern–Levison parameter Λ is an excellent distinction between proper planets and things too small to be proper planets.

PhilW
Taylor Quinta de Vargellas 1987
Posts: 2469
Joined: 14:22 Wed 15 Dec 2010
Location: Near Cambridge, UK

Re: Significant figures

Post by PhilW » 19:26 Mon 20 Jul 2015

But... is or is not a dwarf planet a subtype of planet?

User avatar
jdaw1
Taylor 1900
Posts: 19687
Joined: 15:03 Thu 21 Jun 2007
Location: London
Contact:

Re: Significant figures

Post by jdaw1 » 19:30 Mon 20 Jul 2015

PhilW wrote:But... is or is not a dwarf planet a subtype of planet?
Not.

PhilW
Taylor Quinta de Vargellas 1987
Posts: 2469
Joined: 14:22 Wed 15 Dec 2010
Location: Near Cambridge, UK

Re: Significant figures

Post by PhilW » 19:34 Mon 20 Jul 2015

Daft naming convention then...

User avatar
jdaw1
Taylor 1900
Posts: 19687
Joined: 15:03 Thu 21 Jun 2007
Location: London
Contact:

Re: Significant figures

Post by jdaw1 » 19:40 Mon 20 Jul 2015

PhilW wrote:Daft naming convention then...
If you are going to spend your days remarking on what is stupid in the world, expect to be very busy. (Whether or not you contribute to the cricket/ashes thread.)

Glenn E.
Quinta do Vesuvio 1994
Posts: 3339
Joined: 22:27 Wed 09 Jul 2008
Location: Seattle, WA, USA

Re: Significant figures

Post by Glenn E. » 23:20 Mon 20 Jul 2015

jdaw1 wrote:
Glenn E. wrote:In the future jdaw1 may interpret my use of "planet" in reference to Pluto has a shorter and easier to type abbreviated form of "dwarf planet".
Now this off-topic drivel has been split from the topic from which it was off (aside to the aside of the aside: I’m loving the prepositional torture), we can do the Pluto-is-Pluto-isn’t rant. I’ll show my cards: the Stern–Levison parameter Λ is an excellent distinction between proper planets and things too small to be proper planets.
When the definition of a "planet" requires a special clause to allow Earth, Mars, Jupiter, and Neptune to qualify - but not Pluto - then it is a bad definition.
Glenn Elliott

User avatar
jdaw1
Taylor 1900
Posts: 19687
Joined: 15:03 Thu 21 Jun 2007
Location: London
Contact:

Re: Significant figures

Post by jdaw1 » 23:41 Mon 20 Jul 2015

Glenn E. wrote:When the definition of a "planet" requires a special clause to allow Earth, Mars, Jupiter, and Neptune to qualify - but not Pluto - then it is a bad definition.
If that were true, it would be a bad definition. But it isn’t.

Λ = k × M² / P, where M = mass, P = orbital period, and k is effectively a constant. For the real planets, it’s much much chunkier than 1. For the non-planets, much much smaller. Of the planets, smallest for Mars, at ≈942. Of the non-planets, largest for Pluto at ≈0.00295 then Eris at ≈0.00215. That’s robust.

User avatar
DRT
Graham’s 1948
Posts: 14991
Joined: 23:51 Wed 20 Jun 2007
Location: Chesterfield, UK
Contact:

Re: Significant figures

Post by DRT » 23:52 Mon 20 Jul 2015

jdaw1 wrote:
Glenn E. wrote:When the definition of a "planet" requires a special clause to allow Earth, Mars, Jupiter, and Neptune to qualify - but not Pluto - then it is a bad definition.
If that were true, it would be a bad definition. But it isn’t.

Λ = k × M² / P, where M = mass, P = orbital period, and k is effectively a constant. For the real planets, it’s much much chunkier than 1. For the non-planets, much much smaller. Of the planets, smallest for Mars, at ≈942. Of the non-planets, largest for Pluto at ≈0.00295 then Eris at ≈0.00215. That’s robust.
I read the wiki and I agree with Glenn. I do not understand the detail of the maths, but the line has been drawn in a place where some things are planets and some things are not. That line could equally have well been drawn in a place where the gas giants were planets and the rocks like Earth were not. That is subjective judgement, not a fact.

This is a case of science trying to impose a meaningless rule and then trying to defend itself with flawed logic.
"The first duty of Port is to be red"

Ernest H. Cockburn

User avatar
jdaw1
Taylor 1900
Posts: 19687
Joined: 15:03 Thu 21 Jun 2007
Location: London
Contact:

Re: Significant figures

Post by jdaw1 » 00:15 Tue 21 Jul 2015

DRT wrote:That line could equally have well been drawn in a place where the gas giants were planets and the rocks like Earth were not.
If true, a powerful argument. But not so. Things bigger than 1 are massively bigger than 1, things smaller are very much smaller. No close cases.

Λ determines whether things gravitationally dominate their neighbourhood. Only one thing can. For instance, Jupiter can have Trojans in its Lagrange point, and they’re stable. But if the Trojans should reach ≈10%ish of the mass of the dominant body, things become unstable. So three cases possible.
• Largest object in this orbit large enough for Λ>>1, and Trojans small. Stable. Largest object a planet. Hurray!
• Largest object in this orbit large enough for Λ>>1, and Trojans >10% of largest object. Unstable — quickly falls apart. Problem case doesn’t last long.
• Largest object in this orbit has Λ<<1, so has too little effect on other bodies to dominate them. Welcome to the asteroid belt / Kuiper belt / etc.

Glenn E.
Quinta do Vesuvio 1994
Posts: 3339
Joined: 22:27 Wed 09 Jul 2008
Location: Seattle, WA, USA

Re: Significant figures

Post by Glenn E. » 05:28 Tue 21 Jul 2015

We argue not with the math, but rather with the choice to use that particular line in the sand as the definition. There is no scientific reason to define a planet as an object that clears its orbit, or that when it fails to clear its orbit like Earth, Mars, Jupiter, Neptune, and Pluto, said orbit is stable which conveniently excludes Pluto.
Glenn Elliott

User avatar
jdaw1
Taylor 1900
Posts: 19687
Joined: 15:03 Thu 21 Jun 2007
Location: London
Contact:

Re: Significant figures

Post by jdaw1 » 09:10 Tue 21 Jul 2015

I agree that the phrasing ‘clearing the neighbourhood’ is wrong. It should be ‘dominating the neighbourhood’.

Let’s start elsewhere. Do you agree that many asteroids are not planets? If you think that every pebble in solar orbit is a planet, then the nature of the disagreement is clear. If not, then there are some solar-orbiting natural things that are deemed planets, and some that are not. How would you draw the line?

The problem, as I understand it, is a shortage of more plausible lines. Suggest one.

User avatar
DRT
Graham’s 1948
Posts: 14991
Joined: 23:51 Wed 20 Jun 2007
Location: Chesterfield, UK
Contact:

Re: Significant figures

Post by DRT » 09:23 Tue 21 Jul 2015

I think the geological processes that affect an object is a more plausible argument.

Asteroids and most moons are inert lumps of rock and other stuff. The planets that we call planets plus Pluto are the only objects we know of that are (a) not a satellite of a planet and (b) are or once were geologically active.

I think that would be a better basis than arbitrary maths that don't really mean anything.
"The first duty of Port is to be red"

Ernest H. Cockburn

User avatar
jdaw1
Taylor 1900
Posts: 19687
Joined: 15:03 Thu 21 Jun 2007
Location: London
Contact:

Re: Significant figures

Post by jdaw1 » 09:54 Tue 21 Jul 2015

DRT wrote:I think the geological processes that affect an object is a more plausible argument.

Asteroids and most moons are inert lumps of rock and other stuff. The planets that we call planets plus Pluto are the only objects we know of that are (a) not a satellite of a planet and (b) are or once were geologically active.

I think that would be a better basis than arbitrary maths that don't really mean anything.
The maths has meaning, but this also has merit. And problems.

• Is Eris a planet? Under the DRT definition, the answer has to be ‘no idea’. And no prospect of having an idea for what might be ages. Ditto lots of others.

• If a planet is shattered in an impact, is every pieces of shrapnel (all which have been formed or shaped or changed by geological processes) then a planet?

Glenn E.
Quinta do Vesuvio 1994
Posts: 3339
Joined: 22:27 Wed 09 Jul 2008
Location: Seattle, WA, USA

Re: Significant figures

Post by Glenn E. » 18:06 Tue 21 Jul 2015

jdaw1 wrote:I agree that the phrasing ‘clearing the neighbourhood’ is wrong. It should be ‘dominating the neighbourhood’.
I imagine the meeting where a bunch of astronomers suddenly realized that Earth was no longer considered a planet, and so frantically changed the definition to "dominating" from "clearing" the neighborhood.

"Planet" is a loaded term at this point. If gas giants and telluric objects can both be considered planets simply because they always have been, then there's no reason to create a "scientific" definition that explicitly excludes Pluto. Especially when said definition is explicitly restricted to our solar system. If Astronomers need such a definition (note: they clearly don't since the definition is restricted to our solar system, which isn't going to get any bigger during our lifetimes), they can use a different word. Feel free to make one up that everyone else can ignore.

Re: Eris - "we don't know yet" is a perfectly acceptable answer to "is Eris a planet?"

Further ramblings... what are all these things orbiting other stars? Can't use the IAU definition, so do we have to stop calling them planets? (Hint: yes. Which is dumb.)
Glenn Elliott

User avatar
jdaw1
Taylor 1900
Posts: 19687
Joined: 15:03 Thu 21 Jun 2007
Location: London
Contact:

Re: Significant figures

Post by jdaw1 » 18:56 Tue 21 Jul 2015

I am defending the definition as it applies to our home. It should also apply to other solar systems, at least those with a single sun. Multiples, especially non-hierarchical multiples, might be weird.

User avatar
DRT
Graham’s 1948
Posts: 14991
Joined: 23:51 Wed 20 Jun 2007
Location: Chesterfield, UK
Contact:

Re: Significant figures

Post by DRT » 00:10 Wed 22 Jul 2015

jdaw1 wrote:I am defending the definition as it applies to our home. It should also apply to other solar systems, at least those with a single sun. Multiples, especially non-hierarchical multiples, might be weird.
Or you might just be supporting the making it up as we go along theory. Well done.

The Earth is not flat, and a planet has no scientifically meaningful definition.

Make it up from there.
"The first duty of Port is to be red"

Ernest H. Cockburn

User avatar
jdaw1
Taylor 1900
Posts: 19687
Joined: 15:03 Thu 21 Jun 2007
Location: London
Contact:

Re: Significant figures

Post by jdaw1 » 09:45 Wed 22 Jul 2015

DRT wrote:and a planet has no scientifically meaningful definition.
A particular planet does not, but the word ‘planet’ could.
Glenn E. wrote:Re: Eris - "we don't know yet" is a perfectly acceptable answer to "is Eris a planet?"
Yes, sure. But in that case Pluto would not have been a planet until a few days ago. Is that what you want? Do you want there to have been only one planet until the space age?

Glenn E.
Quinta do Vesuvio 1994
Posts: 3339
Joined: 22:27 Wed 09 Jul 2008
Location: Seattle, WA, USA

Re: Significant figures

Post by Glenn E. » 16:36 Wed 22 Jul 2015

jdaw1 wrote:
Glenn E. wrote:Re: Eris - "we don't know yet" is a perfectly acceptable answer to "is Eris a planet?"
Yes, sure. But in that case Pluto would not have been a planet until a few days ago. Is that what you want? Do you want there to have been only one planet until the space age?
You extrapolate; I did not. I'm perfectly happy saying "our understanding of the solar system is evolving, so for the time being we cannot say for sure whether or not Eris should be considered a planet or some other type of solar object."

I'm far from convinced that our evolving understanding of the solar system needs to have a new definition of a "planet" that seems to have been deliberately created to exclude Pluto. Please explain the need for this new definition before we argue whether or not it is correct. I see no need, ergo the question of whether or not it is correct is moot.
Glenn Elliott

Post Reply

Who is online

Users browsing this forum: No registered users and 4 guests