Dark Energy

[TheFaithfulStone]

Oddly enough, there is no extant thread on this I could find. At least, not with a relevant title.

 

Anyway, my understanding of Dark Energy is that there are two separate models of it.

 

1)Lambda - Dark Energy is the expansive force of the universe itself and is a "cosmological constant" like C or the fine structure constant. It's a fundamental property of the universe.

 

2)Quintessence - Dark Energy is a field that exists in differing strengths throughout the universe. You could have a region of "higher" dark energy with this model.

 

So, am I missing any? What are the positives and negatives for each theory, and could I get me a laymans explanation of them? Is this stuff luminferous aether? There doesn't appear to be much disagreement that it exists, but then...

 

TFS

[Farsight]

Anyway, my understanding of Dark Energy is that there are two separate models of it.

There's a problem of understanding with "ordinary" Energy that needs examination before you worry about Dark Energy, TFS! See Energy Misdefined in Physics at http://nov55.com/energy.html

 

Let me paraphrase: You’re in a 1000 kilogram rocket car in space. You give the gas pedal a squirt and burn a kilogram of fuel to accelerate to 1 meter per second. You then work out your kinetic energy using ½mv² on your calculator and get 500 as your answer.

 

Then you give the gas pedal another squirt, burn another kilogram of fuel to accelerate to 2 meters per second, and work out your kinetic energy as 2000. You can repeat this as much as you like… 4500, 8000, 12500, 18000, etc.

 

But there’s only so much chemical energy in a kilogram of fuel. Each squirt must be adding circa the same amount of kinetic energy, not hugely-increasing amounts. It means KE = ½mv² has to be wrong, and the correct expression is KE = mv. The big deal is that the unit of measure has changed... which means E = MC² has to be wrong. And energy doesn’t get conserved, it gets created and destroyed. The ramifications rumble on forever. It affects everything.

[Jay-qu]

mv is momentum - totally different, if you take the intergral of this you get kinetic energy.. I dont know what any of that had to do with dark energy :hihi: does it have any link with dark matter?

[ronthepon]

Let me paraphrase: You’re in a 1000 kilogram rocket car in space. You give the gas pedal a squirt and burn a kilogram of fuel to accelerate to 1 meter per second. You then work out your kinetic energy using ½mv² on your calculator and get 500 as your answer.

 

Then you give the gas pedal another squirt, burn another kilogram of fuel to accelerate to 2 meters per second, and work out your kinetic energy as 2000. You can repeat this as much as you like… 4500, 8000, 12500, 18000, etc.

 

But there’s only so much chemical energy in a kilogram of fuel. Each squirt must be adding circa the same amount of kinetic energy, not hugely-increasing amounts. It means KE = ½mv² has to be wrong, and the correct expression is KE = mv. The big deal is that the unit of measure has changed... which means E = MC² has to be wrong. And energy doesn’t get conserved, it gets created and destroyed. The ramifications rumble on forever. It affects everything.

 

Hm.

 

Allow me to justify our current science.

 

Firstly, mv , as Jay-Qu said is momentum. That concept seems to have replaced your concept of kinetic energy.

 

Kinetic energy is not a measure of motion. It is a measure of ability of doing work. That's energy.

So it is just not nessecary that there is a linear relation.

 

Secondly, There is very clear and easy proof of the validity of the expression for kinetic energy, ½mv². If you ask me, I will post the proof ASAP.

[TheFaithfulStone]

crackpottery

 

 

Where do you guys come from?

 

TFS

[Farsight]

There is very clear and easy proof of the validity of the expression for kinetic energy, ½mv². If you ask me, I will post the proof ASAP.

 

Yes please, I'd be grateful. Alternatively can you tell me what's wrong with this?

 

Imagine you’re sitting on a 100kg sled on a frozen lake, with a spring gun that fires a puck backwards. The recoil accelerates the sled forwards to a velocity of 0.1 meters per second.

 

Sled and puck have action/reaction so you calculate the energy stored in the spring as 2 x ½mv² -> 100 x .01 = 1 Joule.

 

With the assistance of a snowcat crew running alongside with a supply of pucks you fire the spring gun a further nineteen times in quick succession, and the sled is now travelling at 2 meters per second.

 

You recalculate the energy stored in the spring as 2 x ½ mv² / 20 -> 100 x 4 / 20 =

 

20 Joules.

 

Problem.

 

Sorry if this sounds like it's off topic, but Dark Energy is energy, people never really think about what energy actually is, and I'm new and only trying to chip in where I can.

[kmarinas86]

[math]Energy=Force*Change\ in\ Distance[/math]

 

[math]Force=\frac{Change\ In\ Momentum}{Change\ In\ Time}[/math]

 

[math]Force=\frac{dp}{dt}[/math]

 

[math]Change\ In\ Momentum=mass*Change\ in\ Velocity[/math]

 

[math]Change\ in\ Distance=dx[/math]

 

By the way, if you did not know already, .5v^2 is the area under the line y=x between x=0 and x=v. The area under a line (or a curve) is the result of integration. Advanced math such as this allows us to derive kinetic energy from mass and velocity.

[TheFaithfulStone]

BOERSUN ALMIGHTY!

 

Can we please not talk about basic Newtonian dynamics!? I would really like to hear people's thoughts on the increasing expansion issue.

 

What is dark energy, and how is it distributed throughout the universe, is it a fundamental property of the vacuum or the product of some exotic (as yet undiscovered) particle or field?

 

TFS

[hallenrm]

There's a problem of understanding with "ordinary" Energy that needs examination before you worry about Dark Energy, TFS! See Energy Misdefined in Physics at http://nov55.com/energy.html

 

Thanks a lot Popular for citing a very interesting and useful hyperlink.:hihi:

[hallenrm]

Oddly enough, there is no extant thread on this I could find. At least, not with a relevant title.

 

Anyway, my understanding of Dark Energy is that there are two separate models of it.

 

1)Lambda - Dark Energy is the expansive force of the universe itself and is a "cosmological constant" like C or the fine structure constant. It's a fundamental property of the universe.

 

2)Quintessence - Dark Energy is a field that exists in differing strengths throughout the universe. You could have a region of "higher" dark energy with this model.

 

To me dark energy is the periphery of the knowledge of modern physics; it is essentially a concept introduced to explain phenomena that cannot be otherwise explained. Its a theory, and one must accept it at that level only.!:hihi:

[Farsight]

TLS, don't be so hostile. Perhaps this might be of some use:

 

Mass deforms spacetime. Perhaps a deformation of spacetime is all that it really is, but no matter. A useful analogy is a bowling ball depressing a rubber sheet, whereupon a flicked marble travels a curved course because its space is bent in a higher dimension. Note that matter is thought of as positive energy, whilst gravity is thought of as negative energy.

 

A negative mass would conceivably be a spacetime deformation that made a "peak" rather than a depression. Your marble or a photon would skirt this peak, so it would probably be dark. It would be associated with antigravity that would be thought of as a positive energy, which would push the Universe apart.

 

Can anybody explain my energy problem with the sled and the spring?

[TheFaithfulStone]

I'm not being hostile. You hijacked my thread.

 

Right, I understand negative mass. Looking for people "in the know" to give me the skinny on the difference between Lambda and Quintessence models of dark energy.

 

TFS

[Erasmus00]

Sled and puck have action/reaction so you calculate the energy stored in the spring as 2 x ½mv² -> 100 x .01 = 1 Joule.

 

Not quite. Sled and puck have the same momentum, but quite different energies. The operable equation is

 

[math] E = \frac{p^2}{2m}[/math]

 

So with the same momentum, energy is highly dependant on the mass. This will change your situation somewhat.

-Will

[Farsight]

In a nutshell: The Lambda idea says the expansion effect should diminish as the Universe expands. Quintessense says it increases.

 

I'll start a new thread about my sled and puck.

[IDMclean]

TFS, I have to admit that I am highly skeptical of Dark matter and Energy, however in an attempt to get this all back on track here's some matterial to read regarding the Dark Energy Theorm (hypothesis?)

 

http://en.wikipedia.org/wiki/Dark_energy

http://www.lbl.gov/Science-Articles/Archive/dark-energy.html

http://supernova.lbl.gov/~evlinder/sci.html

 

Hope that helps some.

[Farsight]

Re lambda expansion decreasing and quintessence expansion increasing, it's because lambda is a property of the masses, and quintessence is a property of the gaps in between.

[Bo]

hmm a lot of untrue things in this tread :)

 

Dark Energy: The present day universe appears to ondergo and accelerated expansion. Dark energy is the general name for any stuff that causes this expansion.

Lambda: The simplest way to achieve an accelerated expansion is to fill the universe with a vacuum energy with a constant energy density. This energy density is called the cosmological constant and is denoted by a capital lambda. a curious property of lambda (and the origin of the notion of 'negative pressure') is the following: he universe expands, so that means that volumes expand. Since energy density is defined as energy/volume one wold expect that the energy density decreases as the universe expands. (this is indeed the case for normal matter). However lambda remains constant, thus the expansion of the universe causes work on lambda.

Quintessence models are a class of models for dark energy that effectively behave like a cosmological constant. the big difference is that where lambda is actually a geometric quantity (in the context of general relativity), qunitessence is a field (in fact: a scalar field; meaning it does not carry spin)

so quintessence models are dynamical, where lambda is purely constant.

 

I hope this clarifies stuff.

 

Bo