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Physics/Regarding dark energy

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Question
Hi,

How did the scientists conclude that there are more dark matter and energy than matter & energy in the universe. If we know that dark matter and energy exists and have not fully understood the nature of them, how could we say with certainty that a particular system obey law of conservation of energy as there could be dark energy/matter present in the system. Also is dark energy, matter present only in Space or in earth, atom as well?


Thanks

Answer
Observation of the rotation rates of galaxies tells us that 80% of the matter in galaxies is "dark," meaning that it does not interact with light but its gravitation is there.  We don't know much about it, since it has not been directly observed.  We also observe that the further out you look, the faster things are moving away from us...but as you compare all the distances, it appears that the rate at which it is moving away is accelerating.  The term "dark energy" is used to reference the apparent energy that appears to be filling space and making matter speed up as the galaxies fly away from one another.  Since we haven't directly observed it, either, we have no way to know if it obeys conservation of energy, either.  We do know that dark matter is diffuse and spread relatively evenly throughout the galaxies, but not concentrated in a particular that we can measure.

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Dr. Stephen O. Nelson

Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Education/Credentials
Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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