You said
What is it?Dark matter is well defined, as the property or material responsible for a number of effects that are observable (so far) anomalous gravitational effects on visible matter.
Nobody knows for sure. Dark matter is currently defined in terms of its properties, particularly its mass. That definition doesn't require that much be known about its other physical properties.harry wrote:What is it?
I think there's only a very small chance we got gravity that wrong. We see many different types of evidence, both near and far, that gravity behaves the way GR predicts. Dark matter is very much more likely than a broken theory of gravity.Martin wrote:There is also a good chance that we have gravity wrong once again and there is no "unkown matter". :oops:
First of all, the only things dark matter and dark energy have in common are the word "dark". Otherwise, they are entirely different things, with entirely different properties, effects, and observations. So lets leave dark energy out of it completely.harry wrote:What about if all the dark matter and dark energy was in the form of degerate matter found in ultra dense plasma matter located in compact stars such as Neutron Stars, quark stars and dark stars (black holes).
Sorry, I fail to see the relevance of any of these citations to your speculations about dark matter.harry wrote:G'day Chris
Your statement tells me that you need to read up...
Okay. I'm all read up. My previous observations remain unchanged.harry wrote:G'day from the land of ozzzzz
My point is that you need to read up on the topic.
Thats up to you.
That's a separate discussion. All I asked is that if you disagree with something I say (which is fine), please tell me specifically what you disagree with, and why. It's unreasonable to simply provide a reading list and ask me to figure out what I said that might be wrong... especially if the only thing "wrong" is your interpretation of what I said!harry wrote:G'day Chris
Upto this date I have not seen one person, being all read up.
If you are, than please explain to me the formation of Neutron Stars and the transition to ultra dense plasma matter that has a trapping horizon.
Dark matter is material (matter <g>) that is invisible (has little or no interaction with electromagnetic radiation) but exhibits obvious gravitational effects on normal matter. Its existence is widely accepted due to close correspondence between observation and theory in multiple, independent measurements. It's actual composition is unknown, but the currently most favored theories assume it consists of non-baryonic particles.harry wrote:Please explain the difference btween Dark Matter and dark energy.
No. It seems quite reasonable, and is accepted by 100% of the scientific community. The definitions are based solidly on observation, not on theory.harry wrote:Now! don't you think that definition is a bit odd?
I would argue that our history of science, with respect to fundamental physical laws, shows that we have seldom been wrong. Once the process of understanding nature was approached scientifically, we rather quickly developed accurate descriptions of how things work. Very few of these theories have been thrown out; most have simply been refined with time.Martin wrote:Chances are that our lack of knowledge is a greater suspect. Our history of science clearly supports this conclusion.
When was the last time "non-baryonic particles" were needed to explain an observed phenomenon? Has any non-baryonic matter ever been observed else where in our universe? And our current understanding of gravity cannot explain the expansion rate between observable galaxies.There is really nothing to make me think we don't have a good, solid understanding of gravity.
That dark matter exists is virtually certain. And current theory (well supported by observation) strongly favors non-baryonic matter. And especially important, theories describing its nature are highly testable. So we simply accept that non-baryonic matter is currently the best candidate for dark matter, but far from the only one. I have little doubt that we will know much more about this within just a few years. But my comments about our understanding of cosmology being essentially correct hold no matter what dark matter turns out to be. The most important point is that it exists and interacts gravitationally with matter we can see. The details of its nature are still being discovered. Nobody has set into canon yet what dark matter is, so there is no fundamental science to be found wrong. I very much doubt we are going to discover that dark matter doesn't exist, and that the observations we record will turn out to be from something radically different, like a fundamental misunderstanding about the nature of gravity.Martin wrote:When was the last time "non-baryonic particles" were needed to explain an observed phenomenon? Has any non-baryonic matter ever been observed else where in our universe?
It does if we assume that there is such a thing as dark energy. Again, theories that require dark energy also explain with high accuracy many structural details we see in the Universe, going back to the Big Bang. We don't need to understand all the details to understand, in broad strokes, what physical laws underlie our observations.And our current understanding of gravity cannot explain the expansion rate between observable galaxies.
What gravity is may be a meaningless question. It is defined by what it does, and that we understand very well. Indeed, under GR, what gravity actually is happens to be well understood as a distortion of spacetime. So it's very likely we do know "what" gravity is.harry wrote:We know what gravity can do, but! we do not know what gravity is.
GR tells us that gravity waves propagate at the speed of light. That has been confirmed by several experiments. It would be fairer to say that there is still some debate about the exact speed of gravity than to say we do not know this at all.We do not even know what the speed of gravity is.
Just thought I'd point out, leptons, photons, W and Z bosons, and neutrinos are all non-baryonic matter.Martin wrote:When was the last time "non-baryonic particles" were needed to explain an observed phenomenon? Has any non-baryonic matter ever been observed else where in our universe?