is an eliptical orbit planet X possible?

[rockoon]

But, if there's no observational evidence, then you have no reason to suppose it exists in the first place.

- Timothy

Before I began reading this thread, the entire concept didnt exist for me and as such the probability of their being a jupiter sized Planet X in a massively elongated orbit was zero.

But now that the idea has been brought to my attention, no matter how little evidence there is for the idea the probability of it being true is greater than zero.

 

[lenny]

All orbits are elliptical*.
*to a close approximation

except those that are hyperbola*
*in which case defining "to a close approximation" is a bit more interesting.
?but then even defining "close" in the ellipical case requires resticting attention to two bodies and/or rather short periods of time, no?

 

[lenny]

But, if there's no observational evidence, then you have no reason to suppose it exists in the first place.

absence of evidence is not evidence of absence.

(evidence of absence is, of course; but your claim was based on "no observational evidence"; forgive me if you did not mean "either way".)

 

[lenny]

Before I began reading this thread, the entire concept didnt exist for me and as such the probability of their being a jupiter sized Planet X in a massively elongated orbit was zero.

so you truly believe that your reading this thread has had a major impact on the likely boundary conditions of our local celestial mechanics? to me that sounds a somewhat naive Bayesian argument.

But now that the idea has been brought to my attention, no matter how little evidence there is for the idea the probability of it being true is greater than zero.

Borel (the mathematician) had some interesting things to say on this in his book "Probability and Certainty". i believe he would have said zero, and held to this even in cases of objective probability.

 

[Jekyll]

except those that are hyperbola*
*in which case defining "to a close approximation" is a bit more interesting.
?but then even defining "close" in the ellipical case requires resticting attention to two bodies and/or rather short periods of time, no?

Orbits aren't hyperbola, but if you're going to include half hyperbolas then you should talk about parabolas and the truncated straight line that represents something smacking into the sun.

 

[drkitten]

absence of evidence is not evidence of absence.

"No observational evidence" is often logical evidence of absence.

There is no observational evidence that there's a bear in my refrigerator.

Because bears are very large, if there were a bear in my refrigerator, there would be observational evidence -- I would see it.

Ergo, there are no bears in my refrigerator.

 

[lenny]

"No observational evidence" is often logical evidence of absence.

agreed, although i'd prefer "can be" to "is often".

and i am happy to count dogs that do not bark as evidence.

but in general, having no evidence says little (for either side).

and to be honest, i am more worried about the idea that thinking of something increases the probability that said something exists...

 

[lenny]

you should talk about parabolas and the truncated straight line that represents something smacking into the sun.

agreed, regarding inclusion of parabolic trajectories for completeness; but they are not needed if we are only working "to a close approximation" (and arguably they fall in a set of measure zero).

the straight line is only a (or three) limiting special case(s), not a new class. although this special case causes all sorts of difficulties regarding determinism in classical mechanics.

in practice, of course, many real orbits are poorly approximated by conic sections on astronomical time scales. it is a nice model, of course.

 

[rockoon]

so you truly believe that your reading this thread has had a major impact on the likely boundary conditions of our local celestial mechanics?

I didn't... but now that you mention it.. its now a distinct possibility with a probability greater than zero

 

[thatguywhojuggles]

Is it time to start posting images of sunsets yet?