Black Hole Merger Model

This is certainly one of those threads that really stretches the mind .... imagining 4 dimensional straight-lines that are curved makes one's head a little sore!

Looking at orbits as being planets moving is straight lines is cool and a nice way to look at the universe. However, that does not work for all gravitational effects. A swininging pendulum swings because gravity exerts a force on the weight at the end of the pendulum pulling it down. How can you re-explain Galileo's simple observations without reffering to Gravity as a force?

Bart.

Came across this on a google search.

That General Relativity predicted gravitational waves wasn't seen at first.
In fact it wasn't proven to physicist level rigour until the 1940s.
(and it wasn't until the 60s that the proof was mathematically consistent)

If you keep within the context of Newtonian Physics then gravity is a force as is Electromagnetism.
However when you move into GR it is not.

As has been said, objects follow straight lines in spacetime. The reason this leads to orbits is to do with GR itself.

The straight line objects follow isn't a path through space, rather it is the object's timeline. When in the presence of a large mass near by time lines will tend to wrap around the massive object's timeline.

In a sense, the Earth "exists" around the Sun. What is a tick of the clock on Earth corresponds to moving around the Sun to an outside observer.

All currently observed effects of gravity can be explained by General Relativity. Even mundane stuff such as swinging water in a bucket wasn't fully explained until GR.
A pendulum swings the way it does because its timeline is directed toward the Earth and away from the Earth, over and over again. From an observer stationary with respect to the Earth, who cannot envision time as an extended dimension, this looks like the pendulum swings up and down in 3-space.

In relation to this discussion, there are actually two types of spacetime curvature. The first kind gives rise to gravity, the second is what causes gravitational waves.

The standard model is happy to see gravity as a feature of spacetime so no particle required.

Which Standard Model are you refering to?
The Standard model of Particle Physics or Cosmology.

The standard model is happy to see gravity as a feature of spacetime so no particle required.

Which Standard Model are you refering to?
The Standard model of Particle Physics or Cosmology.

Sorry, Particle Physics.

In relation to this discussion, there are actually two types of spacetime curvature. The first kind gives rise to gravity, the second is what causes gravitational waves.

Can you elaborate on that a bit?

Can you elaborate on that a bit?

Gravitational waves are caused by Weyl Curvature and Gravitation is caused by Ricci Curvature.

Einstein's General Theory shows how matter can generate Ricci Curvature, but not Weyl Curvature.
However under the right conditions Ricci Curvature can generate Weyl, which is how Black Holes create gravitational waves.

The interesting thing is that in the Universe's past the curvature was completely Weyl and as time progressed Ricci Curvature increased.
The progression from Weyl to Ricci is basically an entropic process.

One of the problems with Quantum Gravity is that you can quantise Weyl Curvature, but you can't quantise Ricci.

Sorry, Particle Physics.

The relationship between the Standard Model and GR is an interesting one. Despite what you always hear, Quantum Theory and General Relativity do work together and don't contradict each other.

The only problem is that the Standard Model is a Quantum Field Theory, which were always formulated in flat spacetime until the 80s.
(Which isn't a problem because you rarely need to understand particle physics in a Strong Gravitational Field)

It seems that you can put Quantum Field Theories in a curved spacetime, but it has only been done for a select few spacetimes, because in most spacetimes Feynman diagrams don't work as well as usual.

Son Goku,

The only problem is that the Standard Model is a Quantum Field Theory, which were always formulated in flat spacetime until the 80s.
(Which isn't a problem because you rarely need to understand particle physics in a Strong Gravitational Field)

And the event horizon censures the proceedings anyway.
Can you recommend any literature on Weyl or Ricci Curvature ? I'd like to follow this up a bit more.

I still think nature has something strange to throw at us regarding 'gravitational waves'. I think there is still something that we're missing. "Science without observation" and all that - why have gravitational waves not been observed yet ? - and yes I know it's not a simple matter to observe.
This months Astronomy magazine has a section on how merging black holes can be thrown free of their host Galaxy by a gravitational wave re-bound, however, many Galaxies are the result of mergers, why don't we see any evidence for this eviction of merging black holes? presumably you would need to look for broken galaxies, or does the evicted black hole re-capture it's host galaxy after a period ?

I'll start chewing on the first few syllables and see how they taste.