Re: strings near the speed of light
From: Mark Palenik (markpalenik_at_wideopenwest.com)
Date: 09/01/04
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Date: Wed, 1 Sep 2004 07:12:17 -0500
"tadchem" <tadchemNOSPAM@comcast.net> wrote in message
news:mcadnZ-77rgTEKjcRVn-hA@comcast.com...
>
> "Mike" <no..spam@please.com> wrote in message
> news:SU8Zc.667$Pd2.279302@monger.newsread.com...
> >
> > "tadchem" <tadchemNOSPAM@comcast.net> wrote in message
> > news:TP-dnWZBAp2eeqncRVn-jA@comcast.com...
> > >
> > > "Mike" <no..spam@please.com> wrote in message
> > > news:XSOYc.628$Pd2.259173@monger.newsread.com...
> > > > They consider the quanta of the gravity of general relativity to be
> the
> > > > graviton. But I am not aware of any quanta used for Special
> relativity.
> > >
> > > Special Relativity is a "special case." It is basically a pedagogical
> > > device used to explain basic concepts and principles, much like the
> > > legendary "point mass," "spherical body," and "infinite line." SR is
> > > relativity as considered in the absence of gravitational
interactions -
> a
> > > useful device as it allows handling the physics in terms of Euclidean
> > > geometry.
> > > ...snip
> >
> > Thanks for the reply, but I seem to have missed how it applies my
problem.
>
> In GR, "gravity" is a manifestation of space-time curvature. It is
> inherently not "quantizable." In SR, gravity is ignored completely.
>
> In either case, there can be no quantum of gravity, and therefore no
> "graviton." The graviton is a convenience to those physicists who want to
> deal with gravity in Euclidean coordinates.
Where are you pulling this from? The graviton is the quantization of the
gravitational wave, which physicists admit is spacetime curvature. In fact,
if it weren't for the fact that General Relativity describes gravity, the
problem of a non-renormalizable theory probably wouldn't pop up.
Virtual gravitons, which would mediate the gravitational force, are terms in
a series of perturbations to spacetime, that when completely summed up,
should reduce to GR in a classical limit.
>
> It is NOT a detectable/measurable particle like photons, Fermions or
Bosons.
> A simple change of coordinate systems makes it disappear.
Photons are an example of a boson. Gravitons are spin 2 bosons, and try
telling the people at LIGO that they're not detectable.
>
> > In the mean time, I consider whether in order for a string to increase
> speed
> > it must accelerate and whether that means it interacts with particles
that
> > give it more energy in the process. Perhaps photons (or perhaps
> gravitons?)
> > interact with string/particles to give it more energy as it speeds up.
I'm
> > thinking this may mean that the frequency of a string would increase due
> to
> > the interactions that increase its speed. But this increased frequency
> would
> > appear to be slower than expected due to special relativistic effect, so
> > that the end result would be that the frequency of a string would at
least
> > appear to be invariant with speed and the special relativistic effects
are
> > nullified. This is a question.
I think my last post didn't get crossposted to one of these newsgroups that
my server doesn't carry, but as I said in it, my guess would be that the
properties of a string are more determined by vibrational mode than
frequency. And yes, there is a difference, since
I'm pretty sick right now, and didn't take the time to fully read that last
paragraph you wrote, but if you're saying what I think you're saying, the
string's properties would only be invarient from one particular reference
frame.
>
> I thought string theory postulated that the speed of string (at least
their
> ends) was fixed at c, even at the lowest energy levels. This would seem
to
> make any discussion of "increasing speed" moot. Similarly, "acceleration"
> can only apply to massive particles - and strings are massless.
I don't think it postulates this at all. As far as I know, it uses
something close to normal field theory, but on strings, rather than point
particles. And yes, field theory is what gives us those "virtual particles"
that mediate force interactions, and yes, string theory describes forces in
a kaluza-klein type manner, as curvature of spacetime. The two ideas aren't
mutually exclusive.
>
> Strings can vibrate in different "modes", with the higher energy modes
> displaying higher frequencies - watch children playing with a jumprope
> sometime. The higher frequency/energy modes have points where the string
is
> stationary called "nodes." The higher the frequency, the more nodes are
> present.
>
> > But then again, each interaction that increased the speed of a
> > string/particle would give it a small enough increase that it would seem
> as
> > though the average effect of these interactions has a linear effect with
> > respect to speed.
What? Vibrational mode is independant of reference frame. If it is
vibrational mode that determines the properties of a string, there's no
reason to believe accellerating it would affect the vibrational mode at all.
>
> Since the endpoints of the strings are moving at c, there is no variation
in
> amplitude for the various modes.
Please provide a citation for this. I have never heard of a prediction by
string theory that the end points are moving at c. In fact, that would
violate SR
There shouldn't be variation in amplitude anyway, I should point out.
>The only way for a string to reach a
> higher energy state is for it to absorb enough energy to excite it into a
> specific mode. It will be "invisible" to energies that do not allow it to
> access specified modes of vibration. Basic QM - decidedly non-linear.
If the vibrational mode were to change, either the type of particle, or the
mass, or some fundimental propperty, would change. If this does happen,
it's not something we see every day.
And quantum field theories, of any sort, are hardly basic QM. You have to
take 4.5 semesters of QM at my university before you even touch field
theories - two of those semesters are graduate level courses. And then
there's gauge theory (which string theory is a subset of).
>
> > Yet the appearance of SR is non-linear with speed. So
> > maybe this proves that the above scenario is wrong.
>
> SR is not very relevant to string theory.
Oh, indeed it is. Field theories are always done on Minkowski Spacetime
(which is what brings about the properties of SR). If you just "ignore"
relativity, you're not going to get the right answer.
>SR is more about the difference
> in the appearance of phenomena from different points of view
(preferentially
> called "frames of reference" by relativists) which are moving relative to
> each other at constant speed. Toss relative acceleration of frames of
> reference into the pot and suddenly you are talking GR.
Not necesarrily. You can describe properties of accellerating objects by
looking at their path through Minkowski Spacetime, without resorting to GR.
>
> String theory is more about QM of objects that can exhibit *internal*
> motions - structured objects in which different parts are moving relative
to
> the whole.
Not really, since string field theory must be performed over some kind of
background.
I've actually heard it said that String Theory gives rise to a metric, in
which case geometry, and SR become very important, since it's SR that tells
us when the signs on our Space/time metrics should be.
>
> Keep in mind always that this is just a *conceptual* device - a "model."
> There is no such object as a massless string that we have been able to
> detect.
I'm not sure that strings are supposed to be massless, but that aside,
physicists try to model reality. Strings are meant to describe fundimental
particles, rather than points, and in that sense they're real, since that's
what we expect particles to look like on the right scales.
You are only right in the sense that a bare string, not surrounded by it's
field is probably not a physically real quantity, and only has real meaning
when the string and its field are put together.
>What we *can* do is work out the mathematical physics of the
> motions of an idealized massless string (in elementary dynamics - a
> sophomore level physics or engineering course)
The problem is, the mathematics of string theory isn't quite that simple.
Differential equations are not enough to desribe the properties of string
theory. We get path integrals that aren't exactly solveable (only
approximately), multiplication where the commutative property fails to
hold, non-linear geometry in 11 dimensions, or so, and a bunch of other
things that are in the cutting edge of mathematics.
> and compare the *results* to
> the observed behavior of such things as fermions and quarks. By
recognizing
> similarities we can make extrapolations and quantitative predictions about
> the results of future measurements, allowing us to design experiments.
>
> "Analogies are like ropes. They tie things together well, but you won't
get
> very far if you try to push them."
>
>
> Tom Davidson
> Richmond, VA
>
>
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