This seems like a pretty basic question, and I'm sure the answer (or
at least theories or hypotheses about it) must be presented in some
basic physics or quantum physics books, but I don't remember seeing it
anywhere, and I have read a few (but not carefully or recently).

Anyway, here is the question.  Gravity operates at the speed of light
(I assume or have heard).  Is there a kind of wave that creates
gravity?  Do we have any idea what kind of a wave or particle or
wave/particle it might be, or how it's created?  (i.e., why does all
mass give off this wave, or how does it work?)

In other words, I guess the question really is, what is the basic
modern theory (or what are some widely accepted ideas) of how gravity
works?

Hello tamkins-ga,

The answer appears to be that if or when gravity transmitted through
waves, it is simultaneously transmitted through particles, in the same
way that light is transmitted through waves and particles
simultaneously.

A physics professor asserts in Scientific American that "it isn't
really correct to say that gravity is a wave", since "virtual
gravitons pass between two objects" -- in other words, the force of
gravity is present -- "even when there are no gravitational waves
present (for instance, when the masses are at rest)".  This professor
also indicates that a gravitational wave is a wave "that spreads out
through spacetime" when a particle is accelerated, shaking the
gravitational field.  "The energy and momentum of that gravitational
wave are carried by real gravitons."

"Ask the Experts: Physics - Is gravity a particle or a wave? ....",
answer by Bradley Carroll (October 21, 1999)
Scientific American
http://www.sciam.com/askexpert_question.cfm?articleID=000A5B05-6F98-1C71-9EB7809EC588F2D7

A physicist at Fermilab explains:

"... In quantum theory, each particle acts both as a particle AND a
wave.  This is called duality.  So if there is a graviton, we expect
it to behave both as particle and as a wave as well.

The electromagnetic force, for example, is transmitted by photons, and
light is nothing but a large number of photons.  Photons/light show
wave and particle properties.  (See
http://www.fnal.gov/pub/inquiring/questions/light_dual.html for more
information.)

Scientists expect that gravity functions in a similar way. ..."

This physicist also notes that the graviton has not been detected, and
probably won't be detected soon, though scientists believe that it
exists.

"Questions About Physics: Is gravity a particle or a wave?", answer by
Kurt Riesselmann (last modified 1/13/2003)
Fermi National Accelerator Laboratory
http://www.fnal.gov/pub/inquiring/questions/graviton.html

I hope that this information is helpful.

- justaskscott-ga


Search terms used on Google:

"gravity is a wave"
"is gravity a particle"

[I tried other searches as well, but these resulted in the pages I
have cited.]

---

Request for Answer Clarification by tamkins-ga on 07 Mar 2003 08:29 PST

I need more general information than this.  I wasn't primarily
interested in whether gravity was a wave or particle (I'm familiar
with wave/particle duality), but on the general modern theory (or
theories) of gravity, and how it works.  How is it generated, etc? 
Please refer to my original question (especially the last paragraph). 
Thanks.

---

Clarification of Answer by justaskscott-ga on 07 Mar 2003 17:55 PST

I misunderstood your question when posting my answer.  I thought you
were asking whether gravity is a wave or particle, when you were
actually asking whether gravity is created by a wave or particle -- or
more generally, how gravity is created and works.

Here are three explanations -- all of which are based on Einstein's
general theory of relativity -- which indicate that gravity is caused
by the curvature of space-time by masses.  One explanation compares
general relativity with Newtonian gravity, while another throws
quantum theory into the mix.

"What causes Gravity?", by Martin Hogbin (1998)
University of California Riverside: Department of Mathematics
http://math.ucr.edu/home/baez/physics/Relativity/GR/gravity.html

"D.03 What is gravity?"
[sci.astro] Astrophysics (Astronomy Frequently Asked Questions
Internet FAQ Consortium
http://www.faqs.org/faqs/astronomy/faq/part4/section-5.html

"What is Gravity?", by Doctor Mitteldorf (05/06/2001)
The Math Forum @ Drexel
http://mathforum.org/library/drmath/view/56351.html

I think that these explanations are what you were looking for. 
Gravity is generated not by a "wave" or "particle", but by the
interaction of space-time and masses.


Search terms used on Google:

"what causes gravity"
"what is gravity"

Thanks a lot!  My original question wasn't worded very well - thanks
for sticking with it.  :-)

Hi tamkins

 question:  Gravity operates at the speed of light
(I assume or have heard).  Is there a kind of wave that creates
gravity
   According to Newton's theory of universal gravitation the
  action of gravity was instant.

  Imagine sun changing suddenly
(somehow, may be exploding and splitting into two parts)
 In Newton's theory, we IMMEDIATELY feel the change)

  In modern theory of gravity,  called General Relativity, it would take
  8 minutes before we feel the change. BTW,  Newton was aware of
   this 'action at distance' being 'ugly' but wisely chose not to deal
   with this. Einstein solved the problem when he rewrote equations
   describing Newton  gravity to relativistic (invariant) form.
   Result was a wave equation for gravity.

   So answer is: There is not a wave which creates gravity. Gravity itself
   is described by a wave equation. If we ignore the Quantum complications,
   we can say gravity itself  is a wave.

   With the QM complication, you have a field called Quantum Gravity, which
   is actively pursued, but has no universaly accepted, verified results yet.

   In more details, we can look at close analogy between gravity and
   electromagnetic field. The static field of both is described by the
   Laplace Equation:
   http://www.glossary.oilfield.slb.com/Display.cfm?Term=Laplace%20equation

    Solution of that equations is the well known 'inverse square law', which
    is Coulomb law for attraction/repulsion of electric charges ,
 when 'source' is electric charge and
    is Newton law of gravity when source term is mass.
    
    There is no time term in that equation (it is static)
 and so it applies to situations where sources are not moving 
 (or moving slowly) and any transients died out.

 We now imagine an electric charge 
(causing the electric field) starts moving quickly
 (e.g. oscillating). 

  If we are 'fast enough' - meaning having the right instruments .
  we will detect electromagnetic wave (such as light) being generated.
  (This is described by the Maxwell equations which have the time term)

  It is the same with gravity. Einstein added the time term and obtained
  the gravitational wave equation - Kind of D'alambert's equation.

   see:
  Jean-le-Rond D'Alembert (1717 - 1783)
 ... In 1744 D'Alembert published his Traité de l'équilibre et du mouvement des
 a vibrating string, and again arrived at a partial differential equation. ...
www.maths.tcd.ie/pub/HistMath/People/DAlembert/ RouseBall/RB_DAlembert.html

  Einstein's gravitational equations provides some corrections (small terms
  by which the solution differs) to the Newton's theory. These were verified
  experimentally. It also predicts properties of the gravitational wave.


  Gravitational wave  was not yet detect experimentally to
 general satisfaction, but detection experiments are in progress.

  The search term 'detecting gravitational waves' brings many references, e.g.
  www.maths.soton.ac.uk/relativity/GRExplorer/ Grav_Waves/GW-detection.html

  I did not find a good elementary description on the web, but can recommend a
  book on relativity...

Hi,
after reading the answer and previous comment i have realized that
there wasn't no reference to the String theory. And what is the string
Theory, the quantum theory doesn't take in account the effect of
gravity in particules i think that question for your question is in
the String Theory.


References:

http://theory.tifr.res.in/~mukhi/Physics/string.html
http://superstringtheory.com/
http://www.lassp.cornell.edu/GraduateAdmissions/greene/greene.html
http://www.damtp.cam.ac.uk/user/gr/public/qg_ss.html