Ash asked in Science & MathematicsPhysics · 7 years ago

# Theories of dark energy and matter...?

I know very little about dark energy and matter. What little i have read seems vaguely similar to Maxwell's theory of "luminiferous aether". Could someone compare and contrast these theories?

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• 7 years ago

Aether was proposed to provide a medium to propagate electromagnetic radiation. It works well for that. The problem is that for every thing else, it does not work. The physical properties required make no sense. Lorentz developed what we now call the Lorentz Transform to calculate the motion of the aether relative to another Frame of Reference to explain the observed fact that the speed of light is constant for all observers. That means the aether with the photons moves relative to the observer. Now comes the problem: For the aether to do what it does it must have a Modulus of Elasticity greater than steel. Think of standing in a river of very fast flowing water, it explains perfectly the motion of the small floating twigs (photons) moving past you, but why don't you feel the motion of the water (aether)?

This is why Special Relativity replaced Aether. Einstein re-derived the Lorentz Transform showing that it worked just as well if you assumed that space-time (Einstein's Great Insight) could expand and contract based on the relative motion of observers. Einstein resolved the above paradox, so SR replaced aether.

Dark Energy was predicted by Einstein in General Relativity

DARK ENERGY

Observation: The universe is expanding at an accelerating rate. Fact.

General Relativity: If you crank through the equations, IF space was pervaded by a thin "mist" of energy then that energy would create "Repulsive Gravity." ====> Dark Energy is predicted by General Relativity.

History: When Einstein cranked through GR he found that the universe should have collapsed on itself shortly after the Big Bang. Clearly, that was not what happened, so he added just enough Dark Energy (The concept of Dark Energy did not exist at the time, for Einstein it was a true Fudge Factor, but that is what he actually did, add invisible energy to the universe.) to make the universe steady state. At the time it was believed that the universe was steady state neither expanding or contracting. Einstein believed it and added a Fudge Factor he called the Cosmological Constant to make his calculations match what he believed to be true. Then Hubble showed that the universe was expanding. Einstein called the Cosmological Constant his "Biggest Blunder."

Now, years later we find that there is a need for a Cosmological Constant to "fine tune" GR to match what we see in the universe. It is no longer a Fudge Factor but the Energy Density of Dark Energy in our universe. Its value in Planck Units is 1.38 * 10^-122. When the Cosmological Constant is small, gravity causes a universe to collapse on itself. When the Cosmological Constant is large, the Dark Energy causes the universe to blow itself apart. Our universe is blowing itself apart, but it is close enough to the steady state balance density that the process has taken and will take billions of years.

http://www.ted.com/talks/brian_greene_why_is_our_u...

Dark Matter explains why local groups of galaxies orbit each other in tighter orbits than can be explained by the amount of matter we can see. ====> Some matter must be invisible (Dark), possibly large black holes. No one knows for sure though.

• Dozo
Lv 6
7 years ago

Join the club. We all know very little about dark energy and matter.

Luminiferous aether is a medium to other stuff, expecially electromagnetic radiation. Dark matter shows absolutely no interaction with electromagnetic radiation.