Insights Gravity animation: lessons learned - comments

[edguy99]

edguy99 submitted a new PF Insights post

https://www.physicsforums.com/insights/gravity-animation-lessons-learned-insight-gained-new-questions/

https://www.physicsforums.com/insights/wp-content/uploads/2015/04/gravity_animation-80x80.png

https://www.physicsforums.com/insights/gravity-animation-lessons-learned-insight-gained-new-questions/

 

[Drakkith]

Interesting article. Makes me want to break out my Construct 2 program and see if I can do something similar in it.

 

[Janus]

As per Mercury's orbit. You can get it to precess using only Newton's laws of gravity, if you include other planets in your model and their perturbing effects on Mercury (and to a small degree, the effect due to the oblateness of the Sun. ). What is anomalous about Mercury's precession is not that it exists, but that it is as great as it is. Mercury has a faster precession rate than it should if you use Newton's laws and include these perturbing effects . A first, the discrepancy was blamed on the existence of an, of yet, undiscovered body orbiting closer to the Sun than Mercury, to which the name Vulcan was given. The search for Vulcan lasted for some 56 years, until Einstein was able to account for the difference with GR.

 

[edguy99]

As per Mercury's orbit. You can get it to precess using only Newton's laws of gravity, if you include other planets in your model and their perturbing effects on Mercury (and to a small degree, the effect due to the oblateness of the Sun. ). What is anomalous about Mercury's precession is not that it exists, but that it is as great as it is. Mercury has a faster precession rate than it should if you use Newton's laws and include these perturbing effects . A first, the discrepancy was blamed on the existence of an, of yet, undiscovered body orbiting closer to the Sun than Mercury, to which the name Vulcan was given. The search for Vulcan lasted for some 56 years, until Einstein was able to account for the difference with GR.

You are correct, based on our equinox line, we expect to find a precession of about 5025 arc seconds per century. However, astronomers have observed a precession rate of 5600 arc seconds per century. Using Lagrange and Laplace calculation techniques, the effects of all the other planets contribute an additional 532 arc seconds per century to the precession. Combined with the precession of our equinox reference line, this accounts for 5557 arc seconds per century, which is close to the observed value of 5600, but still short by 43 arc seconds per century. It's the 43 arc seconds per century that relativity deals with.

 

[GeorgeDishman]

I've added a topic request based on this article:

https://www.physicsforums.com/threads/pf-insights-topic-request.812096/#post-5100075

 

[TheDemx27]

Very excited for the modeling of Mercury's movements! Awesome article. In my program I have gravitational perturbations between planets so the orbits are slightly different.

 

[edguy99]

I've added a topic request based on this article:

https://www.physicsforums.com/threads/pf-insights-topic-request.812096/#post-5100075

WRT to your topic request, I am not sure I have the right resources to pull it off, but it would be fun to try.

I have put an image up at http://www.animatedphysics.com/gravity_waves.jpg to clarify a couple of questions.

1. when 2 bodies rotate, gravitational waves on the equator are either plus or cross polarized, but I am not sure which and do they vary over time?
2. there would be no gravitational wave when looking straight up or down from the rotating objects?
3. at say a 45 degree angle up, we would see the same type of wave that you would see on the equator, but they would be less intense, but by how much?

I think knowing the answers to these questions would help considerably in my understanding.

Thanks for the comment.

 

[GeorgeDishman]

WRT to your topic request, I am not sure I have the right resources to pull it off, but it would be fun to try.

I have put an image up at http://www.animatedphysics.com/gravity_waves.jpg to clarify a couple of questions.

1. when 2 bodies rotate, gravitational waves on the equator are either plus or cross polarized, but I am not sure which and do they vary over time?
2. there would be no gravitational wave when looking straight up or down from the rotating objects?
3. at say a 45 degree angle up, we would see the same type of wave that you would see on the equator, but they would be less intense, but by how much?

I think knowing the answers to these questions would help considerably in my understanding.

Thanks for the comment.

Thanks for that, it's exactly what I was wondering too. I would also add another question about the distortion along the 'equator'. Presumably at opposing points there would be a maximum stretch while simultaneously at 90 degrees round from those there would be a maximum compression. However, that suggests to me that at 45 degrees 'longitude' from those points, there should be no compression or stretch but a significant sideways displacement. That isn't mentioned in any of the descriptions I've seen of the nature of gravitational waves. Similarly at 45 degrees 'up' latitude that you mention, there would appear to be an alternating translation away from and towards the pole as well as compression and stretching. The whole thing seems a lot more complex than the simple plane wave version shown on Wikipedia and elsewhere and would be very informative.

Thanks for taking the time to think about the idea, it is appreciated, and sorry for taking so long to reply, I'll need to see if I can switch on email notifications.
best regards
George