No need for dark energy

[Jacques]

The expansion of space is accelerating, space is expanding faster than before. From the supernova obsservation that is a fact.

What I don't understand is why do we need dark energy to explain that acceleration, when ther is a simple explaination:

Gravity is opposed to space expansion. Space expansion happen when gravity is not strong enought like between galaxy cluster. Earlier in the cosmos history cluster where closer together and gravity between cluster was bigger because of smaller distance, but not close enought so the space expansion brought these cluster further apart. If the distance between cluster increased, then the gravity between them decreased, so there was less force acting agains the space expansion giving a net increase in space expansion.

 

I don't know if you understand the idea, it is hard for me to explain that in english, but if you need clarification just ask and I will try to clarify my idea for you.

 

Maybe it is already in the calculations done by cosmologist, but I cant tell.

 

[x(x-y)]

You are assuming that dark energy doesn't exist from the onset - and if that was (were?) the case, then indeed gravity would've slowed the expansion down and we would be seeing a very different picture to the one we see today (i.e. we would see a universe which seemed to be slowing down in expansion or even contracting depending on the time). The need for dark energy is to actually be able to explain how the universe is expanding (and expanding at an accelerating rate as suggested by deep field observations of galaxies and standard candles) - without dark energy we don't really have a beginning of an explanation as to why the universe is expanding.

 

As I understand it too, dark energy may actually appear in Einstein's equations of general relativity in the form of the Cosmological Constant. However, I have very little understanding of Dark Energy as yet (although I have just started a lecture module on "Particle Physics and Cosmology" at university so hopefully I will know more in the coming months) and physicists as a whole don't really know much about it either at the moment.

[mathematic]

The point of dark energy is not to explain the expansion itself, but the observation that the expansion is speeding up.

[Jacques]

The point of dark energy is not to explain the expansion itself, but the observation that the expansion is speeding up.

Yes that the point. Space expansion is natural. It is measured and it is happening everywhere where there is not enought mass outside of galaxy cluster. The acceleration of the expansion is also a given observed by distant supernova. The accepted explaination is there exist a dark energy to accelerate this expansion.

My point is that, there no need for dark energy to explain the accelaration of the expansion.

Gravity is a force who is inversly proportionnal to the square of the distance (Newton). The space expansion is proportionnal to the distance (Hubble).

Inside a galaxy cluster gravity win over space expansion. Between galaxy cluster space expansion win so the distance between cluster increase and if the distance increase the influence of gravity diminish. The reduced influence of gravity, leave more place for the expansion.

I hope you understand what I mean.

[mathematic]

Yes that the point. Space expansion is natural. It is measured and it is happening everywhere where there is not enought mass outside of galaxy cluster. The acceleration of the expansion is also a given observed by distant supernova. The accepted explaination is there exist a dark energy to accelerate this expansion.

My point is that, there no need for dark energy to explain the accelaration of the expansion.

Gravity is a force who is inversly proportionnal to the square of the distance (Newton). The space expansion is proportionnal to the distance (Hubble).

Inside a galaxy cluster gravity win over space expansion. Between galaxy cluster space expansion win so the distance between cluster increase and if the distance increase the influence of gravity diminish. The reduced influence of gravity, leave more place for the expansion.

I hope you understand what I mean.

That doesn't explain acceleration. Without dark energy, the expansion would slow down because of gravity.

[SamBridge]

That doesn't explain acceleration. Without dark energy, the expansion would slow down because of gravity.

But that doesn't make sense either, gravity doesn't cause the fabric of space to accelerate at all anyway, it only changes it's shape, so it would have to be a process that deals with higher dimensions.

[mathematic]

But that doesn't make sense either, gravity doesn't cause the fabric of space to accelerate at all anyway, it only changes it's shape, so it would have to be a process that deals with higher dimensions.

What higher dimensions? It sounds like you are making up new physics.

[Arjun Artro]

The expansion of space is accelerating, space is expanding faster than before. From the supernova obsservation that is a fact.

What I don't understand is why do we need dark energy to explain that acceleration, when ther is a simple explaination:

Gravity is opposed to space expansion. Space expansion happen when gravity is not strong enought like between galaxy cluster. Earlier in the cosmos history cluster where closer together and gravity between cluster was bigger because of smaller distance, but not close enought so the space expansion brought these cluster further apart. If the distance between cluster increased, then the gravity between them decreased, so there was less force acting agains the space expansion giving a net increase in space expansion.

 

 

Okay let's assume that space is expanding when gravity is not strong enough to pull objects together.

But why does gravity lose its grip with time? It's been billions of years since big bang and there's no other force that push objects away . So there must be some sort of energy that overpowers gravity.

[Janus]

Yes that the point. Space expansion is natural. It is measured and it is happening everywhere where there is not enought mass outside of galaxy cluster. The acceleration of the expansion is also a given observed by distant supernova. The accepted explaination is there exist a dark energy to accelerate this expansion.

My point is that, there no need for dark energy to explain the accelaration of the expansion.

Gravity is a force who is inversly proportionnal to the square of the distance (Newton). The space expansion is proportionnal to the distance (Hubble).

Inside a galaxy cluster gravity win over space expansion. Between galaxy cluster space expansion win so the distance between cluster increase and if the distance increase the influence of gravity diminish. The reduced influence of gravity, leave more place for the expansion.

I hope you understand what I mean.

 

As far as our understanding of the laws of physics go, a "natural" expansion that is not driven by some type of energy would expand at a constant rate if you were to remove gravity. Adding gravity will slow the expansion. The fact that gravity falls off with distance just means that its ability to slow the expansion decreases as the universe expands. In other words the rate of slowing would decrease with time (but would never drop to zero). In order to have an expansion that accelerates over time, you have to have something driving it.

 

Now it just might be possible that our understanding is incomplete, that over large distances "natural" expansions do tend to accelerate or maybe gravity itself becomes repulsive over great distances.

 

This is where "dark energy" comes in. It is a placeholder term for whatever we eventually determine causes the universe to behave contrary to our expectations, whether it involves an actual form of energy or an adjustment to our present theories.

 

Your "explanation" seems to fall into the second category, however it doesn't give any explanation as to "why" an accelerating expansion is "natural", considering that present day physics holds that it isn't.

[Jacques]

 

 

As far as our understanding of the laws of physics go, a "natural" expansion that is not driven by some type of energy would expand at a constant rate if you were to remove gravity. Adding gravity will slow the expansion. The fact that gravity falls off with distance just means that its ability to slow the expansion decreases as the universe expands. In other words the rate of slowing would decrease with time (but would never drop to zero). In order to have an expansion that accelerates over time, you have to have something driving it.

 

Now it just might be possible that our understanding is incomplete, that over large distances "natural" expansions do tend to accelerate or maybe gravity itself becomes repulsive over great distances.

 

This is where "dark energy" comes in. It is a placeholder term for whatever we eventually determine causes the universe to behave contrary to our expectations, whether it involves an actual form of energy or an adjustment to our present theories.

 

Your "explanation" seems to fall into the second category, however it doesn't give any explanation as to "why" an accelerating expansion is "natural", considering that present day physics holds that it isn't.

 

You almost understood my point. It is natural for space to expand. I will try to put some math.

Space expansion factor is everywhere the same and I will denote it as a scalar S

Gravity is function of masses and distance. Mass is constant so I will represent gravity with g(1/r^2)

Inside a cluster S - g(1/r^2) < 0 then inside cluster there is no space expansion.

Outside a cluster S - g(1/r^2) > 0 then space expand so r increase and become r'

S - g(1/r'^2) > S - g(1/r^2) then space expansion effect is stronger with time.

[J.C.MacSwell]

 

 

As far as our understanding of the laws of physics go, a "natural" expansion that is not driven by some type of energy would expand at a constant rate if you were to remove gravity. Adding gravity will slow the expansion. The fact that gravity falls off with distance just means that its ability to slow the expansion decreases as the universe expands. In other words the rate of slowing would decrease with time (but would never drop to zero). In order to have an expansion that accelerates over time, you have to have something driving it.

 

 

The unbolded is what Jacques is getting at. The bolded contradicts what was just stated.

 

If the natural rate of expansion (assuming there is one) is being retarded by gravity, but that effect is reduced over time from the expansion, then the expansion will increase over time (accelerate) as it approaches that natural rate.

 

The rate of acceleration will diminish but always be positive.

 

.

 

 

Edit: not sure if that actually fits the data just that it is based on Jacque's assumptions

Edited January 14, 2013 by J.C.MacSwell

[Jacques]

The unbolded is what Jacques is getting at. The bolded contradicts what was just stated.

 

If the natural rate of expansion (assuming there is one) is being retarded by gravity, but that effect is reduced over time from the expansion, then the expansion will increase over time (accelerate) as it approaches that natural rate.

 

The rate of acceleration will diminish but always be positive.

 

 

 

Edit: not sure if that actually fits the data just that it is based on Jacque's assumptions

That is exactly what I mean.

I read about Einstein equation for general relativity, and I was wondering if Lambda is the samething as the scale factor for what I call 'natural expansion'

[WildBill]

Hi,

I'm a Layman when it comes to physics but I have recently reading physics books over the past couple of years.

I have a rather simple question with regard to Dark Matter.

 

Is there a simpler explanation for dark matter. Maybe it does not exist.

 

Time. The rate of passage of time in areas of higher density of mass maybe slower than the rate of passage of time in area of lesser density of mass.

 

Would not this explain why the Universe is expanding at an ever increasing rate. The voids between galaxy clusters are getting bigger, lesser and lesser mass. Therefore time is passing at an ever faster rate.

Galaxy clusters would therefore appear to cluster together , rate of passage of time slower comparably.

 

What do you think about that idea?

[JohnCli]

Why am I a quark

any ways

 

Dark MAter =water

Space = Ocean