Comments on: Gravity, Working As Usual

By: doyle featherston

doyle featherston — Thu, 14 Apr 2011 03:51:53 +0000

Any time an object moves through a medium it is slowed by drag

Pioneer 10 is an object, dark matter is a medium

By: Richard

Richard — Wed, 06 Apr 2011 05:41:56 +0000

Could gravitational waves from merging binary black holes, in principle, rule out or confirm f(R)? I assume higher precision observations of the CMB could also rule out or validate f(R).

By: Sean

Sean — Wed, 06 Apr 2011 05:33:32 +0000

Richard– a “generic” f(R) model is ruled out by tests of GR. But you can make models that are not ruled out, by carefully choosing the function f. See e.g.

http://arxiv.org/abs/0705.1158

By: Richard

Richard — Wed, 06 Apr 2011 04:28:17 +0000

Julianne or Sean,

Do you know if f(R) gravity disagrees with any observational evidence thus far? Are there any deep problems with the theory, or is regular GR safe?

Thanks!

By: jick

jick — Mon, 04 Apr 2011 10:33:46 +0000

Wow, I liked the way the physics arxiv blog talked about Phong Shading as if it’s an esoteric technique developed for special applications. In fact, you can learn about it in any decent undergrad-level computer graphics textbook.

WIN for interdisciplinary study.

By: AnotherSean

AnotherSean — Sun, 03 Apr 2011 21:19:16 +0000

Ron: I agree with you that it was not a crackpot endeavor to understand the anomaly either. I was just amazed that many people took very small deviations from the pattern of a complicated object that isn’t in thermal equilibrium as evidence in a break down in our understanding of gravity or a new force. Calling them crackpots was probably rash, but no more so than their conclusions. For the record, I do expect eventual evidence of this sort, but not at at these distances or energies.

By: Eric Habegger

Eric Habegger — Sun, 03 Apr 2011 19:55:26 +0000

A lot of people prematurely linked the Pioneer anomaly with what is happening at the galactic level with dark matter. Things are never that simple, especially if all other objects in orbit around the sun at that distance don’t act like Pioneer. Now, what WOULD be interesting is to see of there is some correlation between the temperature of space at the galactic periphery and what is observed as dark matter. It just may not be cold enough within our solar system for those effects to take hold.

By: Ron

Ron — Sun, 03 Apr 2011 19:40:13 +0000

@AnotherSean (#6),

Yes, a non-gravitational force/acceleration due to the directional radiation of heat. So, if that explains the anomaly, there is no indication of a problem with the current understanding of gravity.

I don’t mean to imply that we truly understand gravity. I’m just saying that it’s not a “crackpot” endeavor to try to explain what caused the anomaly. By “outside force” I meant other than gravity, such as collisions with particles, radiative pressure, magnetic fields, etc.

By: Thomas Smid

Thomas Smid — Sun, 03 Apr 2011 18:46:00 +0000

I have suggested already a few of years ago that the anomaly is simply explained by the inaccuracy with which the earth’s rotation rate is known. This produces an apparent acceleration of the spacecraft. See http://www.physicsmyths.org.uk/pioneer.htm for more.

By: Torbjörn Larsson, OM

Torbjörn Larsson, OM — Sat, 02 Apr 2011 23:55:53 +0000

RTG rocketry.

By: AnotherSean

AnotherSean — Sat, 02 Apr 2011 18:59:40 +0000

Ron: Outside force or incorrect understanding of gravity? Why not just the disippation of heat?

By: Bill Higgins-- Beam Jockey

Bill Higgins-- Beam Jockey — Fri, 01 Apr 2011 23:14:53 +0000

Thanks for the kind words about my sleuthing. I still wish I knew who created the Pioneer artwork on the U.S. passport. I never did track down the answer, although someone at the State Department must know.

I did ask NASA’s history and graphics people, both at Johnson Space Center and at Ames Research Center (where the book containing the original, and quite good, Pioneer painting was published). Nobody at NASA remembers who painted the original. I also had no luck with e-mail to a number of prominent astronomical artists; they were sympathetic but they didn’t know either.

One thing is clear: The NASA artist demonstrates a much better understanding of astronomy than the passport artist. (Could the latter have been ordered to portray the Earth lit from an impossible angle? )

Bill Higgins
Fermilab

By: Ron

Ron — Fri, 01 Apr 2011 18:28:44 +0000

@AnotherSean,

When Pioneer behaves in a manner that is not predicted, it is either due to an outside force or a basic misunderstanding of gravity. I’d say it’s rather important to know which. (Is Lochness an adjective?)

By: Mandeep

Mandeep — Fri, 01 Apr 2011 15:44:53 +0000

Julianne- yes, i was psyched about that image when i first saw it (when i got a new passport last year). I also had time (once when in waiting room for the Federal Police office in Rio — getting a Brazilian work visa, thankfully) to go through and read all the quotes. And i must say, i liked some of them especially — they really moved me. It’s nice to have a passport that one likes like this, to carry around all the time while travelling. :->
-M

By: AnotherSean

AnotherSean — Fri, 01 Apr 2011 15:13:52 +0000

I can’t imagine what the crack-pots will do without the Pioneer Anomaly. Maybe its time to revisit the Lochness monster, I heard they found its relative in a lake in New Mexico.

By: Jonathan Burns

Jonathan Burns — Fri, 01 Apr 2011 10:08:44 +0000

If this is the explanation, it ought to be marked in history as the first photon drive.