I don't know about yee, but I can't get my head around "dark energy". Now I can understand dark matter after a fashion.......is that the stuff we know is there - to explain the behaviour of the universe we observe? is it that stuff that emits no light? am I nearly there :?

But....whats dark energy...can someone explain in 30 words or less what it is (or could be) - maybe we should have a competition for the brainist contributor to this forum who could achieve the above in plain english (I have looked it up not the net but can't make head-nor tails of it) ....or should I just go back to playing with my telescope...

signed, Declan

very perturbed
Co Laois

or should I just go back to playing with my telescope...

I think you should.

I have a suspicion that future Astronomers will say of the current generation:

"What were they smoking?"

Dark energy is the name we give the mystery force that's acting against gravity to speed up the expansion of the universe when it should otherwise be slowing down. We have no idea what it is really.

A little over 20 words but I presume it's still short enough?

Bart.

Thats a good answer Voyager, It's just that the bit I don't understand is why something with so profound an effect on the observable universe. is a mystery.

Thats a good answer Voyager, It's just that the bit I don't understand is why something with so profound an effect on the observable universe. is a mystery.

Well really because scientists are from earth, and are too intent on using earth as a comparison tool. They think that just because gravity takes place here and on other planets, that it should elsewhere. Yet dark energy goes against this so-called gravity. And it makes up more than 75% of the universe. If anything, gravity should be the mystery, not dark energy.

75% is a lot of nothing we can see, or not see. Gravity and it's effects can be seen - and tested. I don't understand the how scientists can say universe is expanding faster than it should - so there must be extra stuff we can't see and something acting upon it.

it's all terribly perplexing :?

75% is a lot of nothing we can see, or not see. Gravity and it's effects can be seen - and tested.

Well the thing is, gravity is still a theory. There are plenty of scientists who say gravity doesn't exist at all. There are also plenty who say dark energy doesn't exist. But the gist of it all is that dark energy seems to go against gravity and causes the universe to expand. It's all still a mystery because we're just a basic version of the human species, we don't really know much, we just happened to be born in a very unfortunate time in history where we are sort of in the middle of understanding. Maybe in a few thousand years people will have a lot more knowledge and understanding, with less theories and more facts.

75% is a lot of nothing we can see, or not see. Gravity and it's effects can be seen - and tested.

Well the thing is, gravity is still a theory. There are plenty of scientists who say gravity doesn't exist at all. There are also plenty who say dark energy doesn't exist. But the gist of it all is that dark energy seems to go against gravity and causes the universe to expand. It's all still a mystery because we're just a basic version of the human species, we don't really know much, we just happened to be born in a very unfortunate time in history where we are sort of in the middle of understanding. Maybe in a few thousand years people will have a lot more knowledge and understanding, with less theories and more facts.

OK, gravity is not a theory, it's a fact. There is gravity.

Our explanation of that fact is of course theoretical but those theories have stood the test of verification very well. For something to get the honor of being a scientific theory it needs to be very thoroughly tested.

Our current understanding of gravitation probably isn't the whole truth, just like Newton's wasn't the whole truth, but it contains a lot of truth. Within the limits of our ability to test it our theory of gravitation works.

There have been some attemtps to explain the bigger gravitational picture without reverting to Dark Matter by attempting to modify the laws of grviation (MOND) but they have not done well.

OK, gravity is not a theory, it's a fact. There is gravity.

Our current understanding of gravitation probably isn't the whole truth, just like Newton's wasn't the whole truth, but it contains a lot of truth. Within the limits of our ability to test it our theory of gravitation works.

There have been some attemtps to explain the bigger gravitational picture without reverting to Dark Matter by attempting to modify the laws of grviation (MOND) but they have not done well.

By me saying gravity is still a theory, I mean that what we see it as may be completely wrong. We see gravity as an isolated force that caused objects of mass to attract one another. What if one of the dozens of other theories such as the Kaluza–Klein theory is correct and gravitational force is combined with electromagnetic force? Then gravity would not exist, it would be a completely new force that we could not call gravity as it is a totally different force than that which we currently define as gravity.

Our explanation of that fact is of course theoretical but those theories have stood the test of verification very well. For something to get the honor of being a scientific theory it needs to be very thoroughly tested.

Thats the whole point of why some people question gravity. Because it can be seen to have no effect in various environments. Then why does it have effect in other environments? If we can't explain everything then it can only still be seen as a theory albeit a very strong one. There is still a chance that the force does not exist at all and it is something completely different, some other form of energy we have yet to discover. There are plenty of scientists who actually dispute the entire existence of gravity, never mind it being combined with other forces, for example some say objects are pushed and not pulled. That wouldn't just change the theory of gravity, that would be a whole new force, rejecting gravity for a new force, seeing as gravity involves a pull. And because of that, it's still a theory and not fact.

What we can say is a fact is that there is some sort of force that in some occasions has an influence on objects in some sort of way involving movement. We can't say that gravity is the fact, seeing as it has a definition and therefore all the clauses that definition hold must be true.
So yes, fact, there is a force. Theory, the force is gravity. Could be something else.

Well, the question is: does gravity work, or does earth suck... 8-)

The reason I really asked the original question was that I am not convinced we need to create dark energy to explain the behaviour of the observed universe. Gravity works just fine for me. I think that something in the nature of mass and the early universe might explain why and when the universe seemed to expand faster. who knows, maybe the early universe had a density that would not allow faster expansion

Nurse....my medicine please.....

Well, the question is: does gravity work, or does earth suck... 8-)

The reason I really asked the original question was that I am not convinced we need to create dark energy to explain the behaviour of the observed universe. Gravity works just fine for me. I think that something in the nature of mass and the early universe might explain why and when the universe seemed to expand faster. who knows, maybe the early universe had a density that would not allow faster expansion

Nurse....my medicine please.....

People have tried to go that route and no one can get such theories to line up with observation and experiment. Maybe some day someone will but right now the evidence seems to point at empty space having energy. Ironically, we seem to be back at Einstein's much maligned universal constant!

Bart.

Oh I meant to add... if you're looking for good explanations of all these things then I can highly recommend the Asrtonomy Cast Podcast. Their back-episodes are a real treasure-trove of good explanations. The tag line for the show is "looking at not just what we know but how we know what we know" and I'm happy to say the hosts do a good job of living up to that. The main host is the guy who runs Universe Today. You can find the podcasts here: www.astronomycast.com/

Bart.

I've heard of dark matter but not dark energy.

My understanding of dark matter is that it is the invisible material or force that holds everything (galaxies) together while gravity or whatever force (maybe kenetic energy) tries to rip everything (galaxies) apart.

It's the universe's answer to superglue.

I'm guessing dark energy is the product/force of dark matter?

The whole concept of dark matter is still a mystery to science.

Has dark matter/energy anything to do with "Z" particles?


Dark energy is the name we give the mystery force that's acting against gravity to speed up the expansion of the universe when it should otherwise be slowing down. We have no idea what it is really.

Cant we just call it anti-gravity?

Hi

I was listening into a podcast recently about a new theory of Dark Energy that suggested that dark energy was in fact an optical illusion.

The idea being that the light from distant objects is travelling to us though regions of space that are of various densities of matter. When it is travelling through the galactic clusters, the extra matter there makes time travel slower then when it is travelling through the void between the galaxies when time will be travelling faster.

This gives the effect of light seeming to travel further then it actually has travelled and consequently making things seem further away then they actually are.

I wonder if anyone else has heard of this idea? :?

DB

Dave i think the show on Discovery Science that i saw on dark matter/energy did offer up this theory as one possibility.

It's so weird. You would expect galaxies etc to slow down as they get further from the point of origin (can we call it the event horizon?)........but they actually seem to be speeding up.

This flies in the face of the natural laws of physics (as we know them).

There must be some other factor involved.

I cant help but think of the difference between observing the moon and Saturn.

The moon is closer to us then Saturn and appears to travel out of our FOV in a scope slower then Saturn which is further away.

Bad comparison i know........................

Gravity - a simple explanation. It is not a force. It is merely the result of matter curving spacetime. Why? - we don't know yet. A body will continue in a staight line unless acted upon by a force. No force causes a planet to orbit the Sun, it is merely the planet carrying on in a straight line through curved spacetime. Hence an elliptical or circular orbit, depending on the curvature of spacetime. Nearer the massive body (e.g. Sun) spacetime is more curved (inverse squared law). Gravity is the old newtonian way of thinking, Einsteins General Realtivity thought us a new way to think about "gravity", and it is definitely not a force in its own right. Unfortunately in order to explain things to lay people scientists still roll out Newtonian classical forces as being the truth, when they are merely an easier model for us to understand. I am not saying that Einsteins theories are the whole truth and nothing but, merely that they are the most accurate model we currently have of reality (whatever that is.).

Dark Energy is just the current model we have until something better comes along to explain why the Universe is expanding at the rate it is (without Dark Energy the maths just doesn't work). However its not as far fetched as it sounds. Seemingly empty space is teeming with energy and particles popping into existence and anhilating almost simultaneously. Fact in this case is stranger than fiction, as anyone who has studied quantum mechanics can attest.

Gravity - a simple explanation. It is not a force. It is merely the result of matter curving spacetime. Why? - we don't know yet.

Thats interesting, its abit like a doctor treating the symptoms of an illness while not knowing the cause, anyone got any theories?

However its not as far fetched as it sounds. Seemingly empty space is teeming with energy and particles popping into existence and anhilating almost simultaneously. Fact in this case is stranger than fiction, as anyone who has studied quantum mechanics can attest.

Well maybe these particles get a chance to exert a force on each other before they go pop, so the more space, the more particles, the more force, so the whole thing accelerates on and on.
I suppose if I think about it enough, I might be able to explain global warning using this quantum mechanics.

Thats interesting, its abit like a doctor treating the symptoms of an illness while not knowing the cause, anyone got any theories?

Well nobody yet knows why matter has the effect it does on spacetime. Until the LHC comes online and maybe discovers the Higgs Boson (reckoned to give matter its mass) and its properties - then the answer may be forthcoming.

Well maybe these particles get a chance to exert a force on each other before they go pop, so the more space, the more particles, the more force, so the whole thing accelerates on and on.
I suppose if I think about it enough, I might be able to explain global warning using this quantum mechanics.

A simple experiment will prove what I say above, known as the Casimir effect. In fact space itself may be (probably is) quantum in nature. And given that space is expanding (the Universe has to have something to expand into) and space in itself is energetic, therefore energy is also expanding. The polarity (if you will) of this energy however is oppsite to what we are accustomed to i.e. mass etc. therefore it has an opposite effect to normal mass/energy i,e, negative curvature of spacetime resulting in expansion of the Universe. If you follow this through to its conclusion the Universe will continue to expand at a faster and faster rate.
Thats the easiest way I know to explain it - sorry if its not clear - my fault.

I suppose if I think about it enough, I might be able to explain global warning using this quantum mechanics.

What has been the temperature rise (globally) over the last ten years? Anyone got any very hard scientific proof that its catastrophic or is it just something that happens on a cyclical basis regardless of the "human factor", or has it in fact remained constant or even declined? In fact CO2 increases lag a good 50 years behind temperature increases based on ice core studies over the last 2,500 years (so are not in fact the cause but rather the result of warming). Fact: the last mini ice-age happened during the Maunder minimum a period when there were no recorded sunspots for nearly 100 years. I'm all for cleaning up this planet and reducing pollution but please don't use the "myth" of global warming to convince people. Then again maybe "people" are stupid enough to believe the clap trap thats spouted and it will all have a beneficial effect in that they reduce polluting (people generally only think in soundbites and what the media push as fact).

Gravity - a simple explanation. It is not a force. It is merely the result of matter curving spacetime. Why? - we don't know yet. A body will continue in a staight line unless acted upon by a force. No force causes a planet to orbit the Sun, it is merely the planet carrying on in a straight line through curved spacetime. Hence an elliptical or circular orbit, depending on the curvature of spacetime.

Far as i know and understand GRAVITY is a force. There is no bending of space and time involved. We will leave that to black holes.

Planetation gravitational pull (as we know it) keeps all the planets moons in orbit around the planets.

Hence an elliptical or circular orbit, depending on the curvature of spacetime.

I dont agree. I think it is all based upon the strength of the gravitational pull of the bodies involved.

Strong pull= circular orbit............................weaker pull= eliptical orbit.


Lets not start bending time and space until it has been proven that it can be done. To bend time and space...........................you venture into the realm of time travel and worm holes.

Which i for one cant/dont accept as ever being a reality.

I do however think that mankind WILL one day achieve faster then light speed travel.

Gravity - a simple explanation. It is not a force.

You must be redefining English, because the dictionary definition, according to multiple dictionaries is:
'A force of attraction that exists between objects'.

If you want to redefine the English language then fine, assign a name to the phenomenon you are talking about, but don't call it gravity - that is already assigned to a very specific term. That is the reason why it may not exist. It is a set term. It must be 100% accurate to that term. You cannot change the theory and make it no longer follow the terminology, it will then become a new term, i.e. not gravity.

Are we getting stuck on semantics here?

I think what John is saying is that the classical theory of gravity as a force was that it was thought the body itself exerted a gravitational force directly on other bodies which is what Paul still 'believes'. What Einstein 'proves' is that its actually more like the mass of the body exerts a force on the fabric of space time rather than exerting the force on the other body. Think of a basket ball on a trampoline. Now roll a tennis ball towards it. What happens to the tennis ball as it passes the dip around the basketball. The Tennis ball changes trajectory. The gravitation of the basket ball has affected the tennis balls course. The dimple in the trampoline has affected the tennis balls course........The dimple/curveture in space time caused by the basketball has affected the tennisballs course. What happens when you put the tennis ball in the midddle of the tramplone and roll the basketball towards it. Same thing but the basketballs trajectory is much less affected by the smaller dimple caused by the tennisball. Bigger mass, bigger dimple in spacetime bigger gravitational affect. Very simple explanation that fudges some of the reality etc but it gets the basic point across I think.

My parents made babies, it has since been discovered that my theory of making babies was wrong and it was not the stork that delivers them but they are made via some other method. Guess I better come up with a different term and scrap the making babies term

i]You must be redefining English, because the dictionary definition, according to multiple dictionaries is:
'A force of attraction that exists between objects'.

If you want to redefine the English language then fine, assign a name to the phenomenon you are talking about, but don't call it gravity - that is already assigned to a very specific term. That is the reason why it may not exist. It is a set term. It must be 100% accurate to that term. You cannot change the theory and make it no longer follow the terminology, it will then become a new term, i.e. not gravity.[/i]

Thats the puzzle. As we understand it...............dark matter/energry acts upon objects in the complete opposite way to gravity (as we know it).

Hence i feel dark matter/energy should be referred to as "anti-gravity"

I am glad I started this thread, I realise that there are many disiplines that I have got knowlwdge of whatsoever. I do believe that most things are ultimately simple - with just the explanation being complicated. I like the illusion theory caus I suffer from a lot of them darn things meself.

Like the ancients, we might as well argue about the wind, they believed that the trees shaking was the cause of the wind and not the other way around. I wonder if we will ultimately discover the same about dark energy.
It's an illusion :shock:

"Time flies like an arrow, fruit flies like bananas"

You must be redefining English, because the dictionary definition, according to multiple dictionaries is:
'A force of attraction that exists between objects'.

The dictionaries define the Newtonian definition of gravity. Which has been shown to be wrong (maybe a strong word for it). What Collins or Webster put in their dictionaries is their business. It is well accepted that Einsteins definition of gravity is as correct as we can be at this point in time. The fact that you guys are still talking about gravity as a "force" tells you more about the education system than anything else. Newtonian (classical) gravity should no longer be taught in schools, it only confuses people who later find out that it is bunkum i.e. you guys

We've had Relativity theory for close to a hundred years now. Isn't it time to start teaching this in place of classical physics? It's no different than if schools were still teaching chemistry as being the combinations of Earth Air Fire and Water.