The End of Space-Time Symmetry?

[Robh (Rob)]

I found this immensely fascinating.
Physicist Petr Horava's theory to unify quantum mechanics and gravity is opening up a whole new line of research. It might also eliminate our dependency on dark matter and dark energy to explain observations.
I'll leave it to the experts to make comment.

http://www.newscientist.com/article/...ef=online-news

Regards, Rob

[renormalised (Carl)]

Exceptionally interesting article. I can get all the other articles referred to in the snippet but not Horava's....unfortunately I don't have access to Phys Rev D (got all the others A,B,C and E, but not D).

If you want the other articles, let me know.

[CraigS]

Good one, Rob.

Very interesting ...

I think this may lead to his original paper (Jan 2009):

http://arxiv.org/abs/0901.3775
(See attachment, also).

Heavy going on the maths, though (as expected).

More later,
Cheers

[Robh (Rob)]

Thanks Guys,

I have the articles.
Ploughing through them, that's another issue!

Hey Carl, I note the problem of renormalizability of gravity in Horava's paper D.

Regards, Rob

[renormalised (Carl)]

I haven't read it yet. I will though. Hmmmm....so there's some infinities creeping into the equations??

[xelasnave]

Thanks Rob.
I am happy that others finally are starting to realise dark matter may be an illussion created by a determination not admit such a notion seems rather unusual.
Still until it is accepted the force of attraction is an illussion I doubt if the understanding of gravity will move forward. Still at least there is a realisation that GR needs a small adjustment somewhere.
alex

[sjastro]

Originally Posted by renormalised

I haven't read it yet. I will though. Hmmmm....so there's some infinities creeping into the equations??

The infinities don't crop up by changing the nature of the gravitational constant at different scales. It's a "subtle" form of renormalization unlike for example the brutal chopping out of divergent terms that describe the energy of a vacuum so it does not become infinite.

It's a renormalizable theory of gravity, unlike previous attempts to combine gravity and the other forces where it was not possible to renormalize.

An interesting paper, it requires a considerable knowledge of QFT to understand it. I'm still sifting through it.

Steven

[bojan]

Originally Posted by xelasnave

Still until it is accepted the force of attraction is an illussion I doubt if the understanding of gravity will move forward. Still at least there is a realisation that GR needs a small adjustment somewhere.
alex

Alex,
On what exactly you are basing your statement that gravity attraction is an illusion?

And.. No-one, ever said GR is perfect. It is just that we don't have better theory yet, every scientist will tell you that.

[sjastro]

Originally Posted by bojan

Alex,
On what exactly you are basing your statement that gravity attraction is an illusion?

I'm wondering about the same thing.

Steven

[renormalised (Carl)]

Originally Posted by sjastro

The infinities don't crop up by changing the nature of the gravitational constant at different scales. It's a "subtle" form of renormalization unlike for example the brutal chopping out of divergent terms that describe the energy of a vacuum so it does not become infinite.

It's a renormalizable theory of gravity, unlike previous attempts to combine gravity and the other forces where it was not possible to renormalize.

An interesting paper, it requires a considerable knowledge of QFT to understand it. I'm still sifting through it.

Steven

I haven't read the paper, so that's why I asked that question. Whether there were infinities cropping up. So, it's just a subtle readjustment of a few of the parameters and not some attempt to try and "hide" mathematical embarrassments that turn up in equations sometimes.

[renormalised (Carl)]

Originally Posted by xelasnave

Thanks Rob.
I am happy that others finally are starting to realise dark matter may be an illussion created by a determination not admit such a notion seems rather unusual.
Still until it is accepted the force of attraction is an illussion I doubt if the understanding of gravity will move forward. Still at least there is a realisation that GR needs a small adjustment somewhere.
alex

???????????

[bojan]

Originally Posted by renormalised

???????????

!!!!!!!!!!!!!!!!!

[avandonk]

The gravity of the Gravity situation with QM cannot be over emphasised.

I think we are all looking in the wrong place.

When some smart B_a_stard works it out we will all go DUH!

I hope it happens in my life time. I doubt if the person has been born yet.

There is a limit to what one human mind can comprehend.

Does anyone here think that the human mind can comprehend itself? Let alone the Universe!

Bert

[CraigS]

Originally Posted by bojan

!!!!!!!!!!!!!!!!!

Hang in there, guys !!
Let's look at the real physics, first !!

[CraigS]

Originally Posted by sjastro

It's a "subtle" form of renormalization unlike for example the brutal chopping out of divergent terms that describe the energy of a vacuum so it does not become infinite.

Steven

Hi Steven;
Whereabouts does this occur ? (Ie: which theory etc?)

Cheers

[sjastro]

Originally Posted by CraigS

Hi Steven;
Whereabouts does this occur ? (Ie: which theory etc?)

Cheers

Craig,

Are you familiar with use of Hamiltonians in Quantum Mechanics?
http://en.wikipedia.org/wiki/Hamilto...ntum_mechanics)

The Hamiltonian is an operator which defines the total energy of a system (the sum of it's kinetic and potential energies).

In Quantum Field Theory the definition of a Hamiltonian is not as straigthtforward and is based on the creation and destruction of virtual particles in a field.
The experimental verification of this concept is the Casimir effect
http://en.wikipedia.org/wiki/Casimir_effect

When the Hamiltonian is applied to a vacuum, the total energy is found to be infinite. A vacuum should in fact be a system in it's lowest energy state.
http://en.wikipedia.org/wiki/Vacuum_energy

The way out of this conumdrum is to define a renormalized Hamiltonian where the term in the Hamiltonian that produces the infinite term is chopped out. The physical significance of this operation is vague.

In other applications of renormalization such as Quantum Electrodynamics or the attachment in this thread, renormalization has a physical significance. The divergence is caused by out of scale or non quantum mechanical effects which can be removed without destroying the integrity of the theory.

Regards

Steven

[CraigS]

Originally Posted by sjastro

Craig,

Are you familiar with use of Hamiltonians in Quantum Mechanics?
http://en.wikipedia.org/wiki/Hamilto...ntum_mechanics)

The Hamiltonian is an operator which defines the total energy of a system (the sum of it's kinetic and potential energies).

In Quantum Field Theory the definition of a Hamiltonian is not as straigthtforward and is based on the creation and destruction of virtual particles in a field.
The experimental verification of this concept is the Casimir effect
http://en.wikipedia.org/wiki/Casimir_effect

When the Hamiltonian is applied to a vacuum, the total energy is found to be infinite. A vacuum should in fact be a system in it's lowest energy state.
http://en.wikipedia.org/wiki/Vacuum_energy

The way out of this conumdrum is to define a renormalized Hamiltonian where the term in the Hamiltonian that produces the infinite term is chopped out. The physical significance of this operation is vague.

In other applications of renormalization such as Quantum Electrodynamics or the attachment in this thread, renormalization has a physical significance. The divergence is caused by out of scale or non quantum mechanical effects which can be removed without destroying the integrity of the theory.

Regards

Steven

Hmm...
No, unfortunately I'm not familiar with the use of Hamiltonians in Quantum Mechanics, (!!), but I do get what you've explained (& thank you for that). I'll have a read of the links & learn more.


I'm now beginning to understand what's going on behind the scenes (in the maths) when the string/quantum theorists say "infinities" occur. Giving the term the chop, (just to eliminate the infinite resultant), surely requires justification, though. As you say it does "destroy the integrity of the theory".

- Oh well, I guess as in most areas, no theory is perfect, and most do live in that world, huh ?

Good that this theory handles it more gracefully, though.
Interesting.

Cheers

[CraigS]

Originally Posted by xelasnave

Thanks Rob.
I am happy that others finally are starting to realise dark matter may be an illussion created by a determination not admit such a notion seems rather unusual.
Still until it is accepted the force of attraction is an illussion I doubt if the understanding of gravity will move forward. Still at least there is a realisation that GR needs a small adjustment somewhere.
alex

Alex;
I know of 3 different types of reality:

1) Physical Reality - eg: Jack Russel dogs exist because they can be measured, weighed and charaterised, repeatedly by anyone (not just me);

2) Reality in one's own mind - eg: "I imagined that giant Jack Russels exist then I observed a big mountain that must've been caused by a giant Jack Russel. So therefore, they're real (but nobody else knows that, except me). A better example without the irony may be feeling hungry - hunger is real, folks but when I'm hungry I'm the only one who knows it;

3) Reality by Concensus - what politicians practise - eg: "Giant Jack Russels exist because me, my mate and everyone else agrees that they do - so they are real".

But Gravity (or the 'force of attraction) falls well and truly into (1) above. ?? Illusion ?? - Only if one's mind is in either of the other two realities !!

Cheers

PS: A topic for a separate post, methinks !!

[renormalised (Carl)]

Originally Posted by CraigS

Alex;
I know of 3 different types of reality:

1) Physical Reality - eg: Jack Russel dogs exist because they can be measured, weighed and charaterised, repeatedly by anyone (not just me);

2) Reality in one's own mind - eg: "I imagined that giant Jack Russels exist then I observed a big mountain that must've been caused by a giant Jack Russel. So therefore, they're real (but nobody else knows that, except me). A better example without the irony may be feeling hungry - hunger is real, folks but when I'm hungry I'm the only one who knows it;

3) Reality by Concensus - what politicians practise - eg: "Giant Jack Russels exist because me, my mate and everyone else agrees that they do - so they are real".

But Gravity (or the 'force of attraction) falls well and truly into (1) above. ?? Illusion ?? - Only if one's mind is in either of the other two realities !!

Cheers

PS: A topic for a separate post, methinks !!

A separate post....the philosophical definition and consequences of reality.

But just as an aside, points 2 and 3 could be lumped into one "catch all" description as "the reality of delusion"

Especially when point 3 is taken into consideration

[xelasnave]

Originally Posted by bojan

Alex,
On what exactly you are basing your statement that gravity attraction is an illusion?

And.. No-one, ever said GR is perfect. It is just that we don't have better theory yet, every scientist will tell you that.

Hi Bojan I though folks saw GR as somewhat perfect but maybe I have formed an incorrect idea given your statement. I do feel there are many who hold it up to be the key to all understanding and in that regard have maybe elevated it to a level higher than its author believed it could ever reach. For me it is one of the things out there one must take into account when discussing the universe, its origins etc. and I would rather deal with it than introduce religion in an attempt to find an answer.

I maintain the force of attraction is not proven and to this end I have searched for an experiment that proves such a force is real, and over the years I have asked for someone to point to an experiment that shows attraction is a force. To date I have no knowledge of any experiment that shows there is a force that we call attraction....and so I say there is no force of attraction but happy to hear why I may be misguided. I have followed your advice and read and read upon physics and although I am old and useless I can follow how we have arrived at where we are today..

Things work within fields and field can only work via particle flow and push I suggest... I am not advocating an electric universe by the way

I do not think particles or bodies "attract" as I can envisage no mechanism where one body "calls" to another in effect saying..."come here"..

Irrespective of how folks wish to exclaim that attraction is obvious..look at magnets etc I simply say is there an experiment that demonstrates an interaction between bodies can be labeled "attraction" and if such labeling is to be used then I inquire..what is the mechanical process that takes place... things do not happen as if by magic so if attraction is to be held up as a force I simple ask what entitles us to label something as "attraction".

I do admit my preoccupation with a push universe has probably made me a little one sided on this issue. However if we are to be scientific and invoke a force such as attraction I simply say it must be proven before we happily use the term to describe an observation that shows two objects moving toward each other...everyone assumes they are attracted I ask how..if how cant be estqablished then I see no reason to simply assume they attract each other.

Now I have lowered my shield you may strike hard at any part you regard as exposed to correction...but please be gentle

I have to go and help someone so I may have to edit when I get to read what I have said.

alex