- #1
alanzhu
- 7
- 0
Is it right?Is it the result of Mach's principle in GR?
Originally posted by alanzhu
Is it right?Is it the result of Mach's principle in GR?
Originally posted by Ambitwistor
the scalar field needed to comply with experiment seems kind of artificial)
Originally posted by Ambitwistor
I'm not talking about the existence of extra couplings; it's easy to cook up theories that have them (e.g. dilatons in string theory, Kaluza-Klein theory, etc.). The question is whether there is a natural mechanism to drive the field to a stable value compatible with observation.
Originally posted by alanzhu
Could this theory explain dark matter? I mean is it possible that there is no dark matter definitely. Because the gravitation constant is not a real constant, the prediction made by GR may be totally wrong.
Originally posted by Ambitwistor
...scalar-tensor theories can account for the expansion of the universe without resorting to dark matter...
Originally posted by jeff
Sorry, but are you referring to brans-dicke scalar-driven inflation (whose relation to this thread is unclear to me), or scalar-tensor theories of gravity producing cosmological features similar to those arising from presence of dark matter?
MaxPolun said:I recently ran across a talk on this very subject (well... more generally can modified gravity eliminate dark matter): http://online.itp.ucsb.edu/online/lens06/carroll/
Chris Hillman said:Hi, Max,
I just glanced at a few of the slides and didn't see any mention of Brans-Dicke theory!
BTW, due to inexperience in this forum, I posted in a thread from 2003; this caused confusion in another thread where I did the same thing, so I apologize in advance for any confusion I might have caused here. In future, I think I'll try to start new threads should I notice other long past questions here which I wish to comment on.
Chris Hillman
Brans-Dicke theory is an alternative theory of gravity that was developed in the 1960s by physicists Carl Brans and Robert Dicke. It proposes a different mathematical framework for understanding gravity, in which the strength of the gravitational force is not a fixed constant but is instead determined by a field called the "scalar field". This theory is an alternative to Einstein's theory of general relativity.
Brans-Dicke theory differs from general relativity in several key ways. Firstly, in Brans-Dicke theory, the gravitational constant is not a fixed number but is instead determined by the scalar field. Secondly, this theory predicts that the gravitational force becomes stronger at very large distances, while general relativity predicts that it becomes weaker. Finally, Brans-Dicke theory introduces a new term in the equations of motion that allows for the possibility of a non-zero cosmological constant, which is not present in general relativity.
There is currently no experimental evidence that definitively supports Brans-Dicke theory over general relativity. However, there are some observations that this theory can potentially explain better than general relativity, such as the accelerated expansion of the universe and the existence of dark matter. Additionally, some scientists argue that Brans-Dicke theory is a more elegant and mathematically consistent theory than general relativity.
If Brans-Dicke theory is proven to be a more accurate description of gravity than general relativity, it would have significant implications for our understanding of the universe. It could potentially change our understanding of the origin and evolution of the universe, as well as the behavior of objects in extreme gravitational environments, such as black holes. It could also have practical applications, such as improving our ability to predict and control the motion of objects in space.
Like any scientific theory, Brans-Dicke theory has its limitations and challenges. One major limitation is that it has not yet been experimentally confirmed, so it remains a theoretical possibility rather than an established fact. Additionally, this theory has many free parameters that can be adjusted to fit different observations, which some scientists view as a weakness. Finally, there are some unresolved mathematical and conceptual issues within Brans-Dicke theory, such as the "strong singularity problem", that continue to be the subject of ongoing research and debate.