Hi guys,

I am new to the forum, so I just thought I would throw a spanner in to see if it jams up any tooth wheels...

Some 400 years ago Johannes Kepler formulated the laws of planetary motion, these laws stated that

v = \sqrt{\frac{GM}{r}

basically says that orbital velocity is a function of the radius, and that planets move slower the further out they are, but was he right?

Do any of you skeptics see why Kepler might have been wrong?

PS: The latex opening and closing statements don't seem to be working on my browser.

beejewel wrote:Do any of you skeptics see why Kepler might have been wrong?

Why do you think Kepler might have been wrong and what evidence do you have to support your view?

Why do you think Kepler might have been wrong and what evidence do you have to support your view?

Firstly it is not my intention to present you with evidence in the case against Kepler, instead I hope to provoke your thoughts into seeing the other solution for yourself, and once you have seen it you will indeed feel enlightened if there is such a thing in the world of non believers.

At first glance planets appear to be travelling in closed elliptical orbits, so why was it assumed that planets have velocity and not simply a speed?

It seems likely Kepler made the assumption that the planets had velocity in the direction perceived by him standing on earth.

If we assume (and I shall show later why this assumption is wrong) that the planets move in closed orbits, there ought to be two solutions for velocity, one positive and the other negative. i.e. it is equally valid to say the planets move forwards as it is to say that the planets move backwards (providing the orbit is closed).

Fortunately thanks to the arrow of time planets do not travel in closed orbits, instead they travel along helical paths, which means there is absolutely no ambiguity about the direction of travel. Think about this for a moment and you will realise which direction planets move. Kepler had a 50/50 chance of getting it right, but failed.

With the exception of Mercury and Mars, all the outer planets are moving backwards with increasing velocities.

beejewel wrote:With the exception of Mercury and Mars, all the outer planets are moving backwards with increasing velocities.

How do you define "backwards" in space.
Do you mean "moving forwards in the opposite direction to another body?"

beejewel wrote:

Why do you think Kepler might have been wrong and what evidence do you have to support your view?

Firstly it is not my intention to present you with evidence in the case against Kepler, instead I hope to provoke your thoughts into seeing the other solution for yourself, ...

What "other solution" would that be?

...and once you have seen it you will indeed feel enlightened if there is such a thing in the world of non believers.

You seem tombe implying that you are religious. Is that so?

At first glance planets appear to be travelling in closed elliptical orbits, so why was it assumed that planets have velocity and not simply a speed?

Any planetary motion needs shoud be described by a velocity, not just a speed.

It seems likely Kepler made the assumption that the planets had velocity in the direction perceived by him standing on earth.

If we assume (and I shall show later why this assumption is wrong) that the planets move in closed orbits, there ought to be two solutions for velocity, one positive and the other negative. i.e. it is equally valid to say the planets move forwards as it is to say that the planets move backwards (providing the orbit is closed).

Fortunately thanks to the arrow of time planets do not travel in closed orbits, instead they travel along helical paths, which means there is absolutely no ambiguity about the direction of travel. Think about this for a moment and you will realise which direction planets move. Kepler had a 50/50 chance of getting it right, but failed.

You are confused.

With the exception of Mercury and Mars, all the outer planets are moving backwards with increasing velocities.

Incorrect.
EDIT: In fact, Pluto is the odd one out in the solar system in terms of direction of orbit. That is because it is, in fact, part of the Oort cloud of planetessimals and space-rocks, so was not formed from the planetary nebula, like the 8 major planets, including Earth and Mars.

Welcome to the forum!

beejewel wrote:

Why do you think Kepler might have been wrong and what evidence do you have to support your view?

Firstly it is not my intention to present you with evidence in the case against Kepler, instead I hope to provoke your thoughts into seeing the other solution for yourself, and once you have seen it you will indeed feel enlightened if there is such a thing in the world of non believers.

er..thanks.

beejewel wrote:
At first glance planets appear to be travelling in closed elliptical orbits, so why was it assumed that planets have velocity and not simply a speed?

They don't 'appear' to be travelling in eliptical orbits. Observations from the Earth show that the planets move all over the place. Taking the Sun as a preferred frame and plugging in eliptical orbits reproduces the apparent motion as observed from Earth.
As to 'velocity' and 'speed' - I have no idea what point you are making.

beejewel wrote:
It seems likely Kepler made the assumption that the planets had velocity in the direction perceived by him standing on earth.

No. The eliptical orbits are viewed from the Sun's rest frame.

beejewel wrote:
If we assume (and I shall show later why this assumption is wrong) that the planets move in closed orbits, there ought to be two solutions for velocity, one positive and the other negative. i.e. it is equally valid to say the planets move forwards as it is to say that the planets move backwards (providing the orbit is closed).

No idea what you mean.

beejewel wrote:
Fortunately thanks to the arrow of time planets do not travel in closed orbits, instead they travel along helical paths, which means there is absolutely no ambiguity about the direction of travel. Think about this for a moment and you will realise which direction planets move. Kepler had a 50/50 chance of getting it right, but failed.

ditto

beejewel wrote:
With the exception of Mercury and Mars, all the outer planets are moving backwards with increasing velocities.

ditto

It's all triangles.

How do they work?

Hi SteveBee

Why is this thread still in a science forum? IMO, it belongs, along with several recent physics forum threads, in the pseudoscience forum.

Planets are, like, big magnets, or something.

If the planets were not moving in the elliptical orbits described by conventional science, we wouldn't be able to send spacecraft to and past them with the accuracy we do. An examination of the accuracy required for the New Horizons mission to Pluto shows just how accurately we describe the orbits of the planets, even though the initial descriptions by Kepler had inherent measurement errors.

laklak wrote:Planets are, like, big magnets, or something.

Aye.

I'm buying folks!

Woohoo! It's been far too long since we had a good physics pub thread!

I'll have a pint with a pint chaser, Campermon!

Weaver wrote:Woohoo! It's been far too long since we had a good physics pub thread!

I'll have a pint with a pint chaser, Campermon!

Here you go

I'm currently enjoying;

ooo, I'd love a decent pint of cider! And one for yourself, landlord.

Decent cider eh?...

You'll touch the mind of god...
You'll run around with no trousers...
You'll fall over...
Not necessarily in that order.

beejewel wrote:Do any of you skeptics see why Kepler might have been wrong?

He wasn't wrong, just not completely accurate. Einstein pointed out his inaccuracies and explained Mercury's orbit in the process.

Oh... and...

Don't worry, for most of you guys it won't make any difference which way the planets rotate, just enjoy your cold ale and get on with whatever you are doing. If anyone here is really concerned about which way the planets rotate, just send me a PM, I would be happy to explain why it matters.