Elegant Universe Questions
During the Career Week we got the following questions:
My students and I are trying to study The Elegant Universe in class.
However, there is much I am limited in helping them with.
Here are several questions the students have researched,
discussed with me and we still need a clarification if possible.
Thanks Again for communicating with us on these topics.
Bob Mirro
Westhampton Beach High School
Westhampton Beach, NY
__________________________________________________________
1. Why would (or does) string theory seem to create a less chaotic
space-time relationship as general relativity and quantum mechanics
are melded together ? [Mike and Kristen]
2. What made theorists choose strings resonating in 10 or 11 dimensions
over other topologies or analogies to explain the theory of
superstrings ? [Mike and Kristen]
3. Why does grand unification have to be the unification of all forces
into one ? Why can't "it" (the unification) connect the nuclear weak
force and electromagnetic due to their repulsive nature and separately
connect the nuclear strong force with the gravitational force due to
their attractive nature ? [Mike, Kristen]
4. Since the strings vibrate, do they have specific definable frequencies ?
If so, how does the theory correlate these individual frequencies
to actual particles or objects ? [Jason and Andrew]
5. What technology, if any, is in development to test hypothesis of grand
unification and superstrings ? [Jason, Andrew]
6. a) Student Comment: During The Elegant Universe, Brian Greene explained
that Einstein came up with a theory of a space-time fabric he embodied
in the general theory of relativity. Greene also explained this
space-time fabric as something like a trampoline at which all
celestial bodies rest on thereby creating ripples and curves in space
and time.
6. b) Question: If our universe is constantly expanding, won't changes in
the ripples and curves of the space-time fabric cause our gravity to
change or fluctuate as well ? [Brittany and Gisela]
7. Why 11 dimensions and how can the need for these dimensions and
analogies for qualifying their existance be explained in laypersons
terms rather than only exotic mathematical terms ? [Leanne,
Sheila, Nick]
8. Is the mechanism for understanding the underlying cause of the
"vibration" of strings well understood - or is it simple just described
by energy analogies and mathematics ? [Leanne, Sheila, Nick]
9. a) With regard to supersymmetry, what is it that makes the particle's
"partners" so heavy ? And...
9. b) If these shadow particles are proposed to be so "heavy", it seems
counter intuitive that they are also hard to see - why is it that
they are hard to see ? [Leanne, Shelia, Nick]
My colleague Mark Jackson (who is a string theorist also with interests in cosmology) provided the following answers:
__________________________________________________________
1. Why would (or does) string theory seem to create a less chaotic
space-time relationship as general relativity and quantum mechanics
are melded together ? [Mike and Kristen]
The strings are extended objects, unlike point particles. So as they
move around, small disturbances in the spacetime fabric aren't as
significant to a string. In fact it was shown (in part by Greene) that
spacetime can actually rip apart by small amounts but the string is
insensitive to this since it 'surrounds it' with its loop before the
rip can spread.
2. What made theorists choose strings resonating in 10 or 11
dimensions
over other topologies or analogies to explain the theory of
superstrings ? [Mike and Kristen]
If the string obeyed the classical laws of physics, 10 or 11 would not
be picked out as special - the string could vibrate just fine in any
number of dimensions. It is when you add quantum mechanics that there
are huge problems unless the string resonates in 10 dimensions (it was
later found that a string in 10d was actually an approximation to a
membrane in 11d). So to unify gravity with quantum mechanics, you seem
to need 10 or 11 dimensions.
3. Why does grand unification have to be the unification of all forces
into one ? Why can't "it" (the unification) connect the nuclear weak
force and electromagnetic due to their repulsive nature and separately
connect the nuclear strong force with the gravitational force due to
their attractive nature ? [Mike, Kristen]
The word unification ('uni-') suggests everything should be
connected into one overall theory. Let's say you combined the laws of
physics into two types like you suggest (either QM and gravity, or
'attractive' and 'repulsive', or any other two categories) - so when
does nature stop using one and start using the other? Unification
means these are really just manifestations of the same thing which
happen to look different in certain circumstances. For example, blue
light and red light look different - but they are both electromagnetic
radiation with just slightly different wavelengths, so you have
'unified' them. Then microwaves seem to behave completely differently
(we can't see them, they pass through your container to heat things up,
etc) but actually that's exactly the same thing with a frequency which
is different from visible light so our eye just can't see it. So you
have unified that with them. And so on. So the different forces of
nature all look very different to us but we think they are all just
different manifestations of the same basic law of physics - which we
are trying to figure out, from strings or otherwise.
4. Since the strings vibrate, do they have specific definable
frequencies ?
If so, how does the theory correlate these individual frequencies
to actual particles or objects ? [Jason and Andrew]
The best way to think of this is just from a musical instrument - you
have a string on a guitar, and it has a fundamental harmonic
(corresponding to a half-wavelength, since the endpoints of the string
are fixed). Then the next allowed harmonic is a complete wavelength,
and then 3/2 of a wavelength, etc. It's exactly the same thing with
superstrings - there is a lowest allowed vibration, then one on top of
that, etc. Each of these vibrations corresponds to a particle that you
would see - so if it is wiggling one way it is an electron, another way
it is a quark, etc. And the more wiggling, the more energy on the
string, and the more massive the particle.
5. What technology, if any, is in development to test hypothesis of
grand unification and superstrings ? [Jason, Andrew]
Well as you probably are aware from Greene's show there isn't any way
we could test string theory from accelerators in the forseeable future.
But there is the very exciting prospect that we may see string theory
in the sky from 'cosmic strings' - giant strings which are stretched
across the sky and which may not only give evidence of string theory,
they would give us information about extra dimensions and other
parameters in the theory. Since I am actually one of the researchers
in this area, I have some popular articles on these cosmic strings
linked from my web page: http://home.fnal.gov/~markj/.
6. a) Student Comment: During The Elegant Universe, Brian Greene
explained
that Einstein came up with a theory of a space-time fabric he embodied
in the general theory of relativity. Greene also explained this
space-time fabric as something like a trampoline at which all
celestial bodies rest on thereby creating ripples and curves in space
and time.
6. b) Question: If our universe is constantly expanding, won't
changes in the ripples and curves of the space-time fabric cause our gravity to
change or fluctuate as well ? [Brittany and Gisela]
Well it is gravity that is making the spacetime expand and it is
quantum mechanics that makes the ripples on the spacetime fabric.
These happen at such different scales (spacetime only expands on really
large scales, and the ripples are only at small scales) that most of
the time they don't really need to talk to each other, and there's no
problem. So gravity doesn't really fluctuate.
7. Why 11 dimensions and how can the need for these dimensions and
analogies for qualifying their existance be explained in laypersons
terms rather than only exotic mathematical terms ? [Leanne,
Sheila, Nick]
Well as explained in #2 it is the quantum mechanics that requires the
10 dimensions. Unfortunately you need some math to understand why, but
the answer is basically the following. Imagine the surface that a
string sweeps out as it moves through time - this surface is called a
'worldsheet'. For stringy physics to make sense, you need to be able
to stretch the worldsheet any way you please. Classical physics is
happy to let you stretch it, but quantum mechanics will not allow you
to stretch the worldsheet unless there are 10 dimensions!
8. Is the mechanism for understanding the underlying cause of the
"vibration" of strings well understood - or is it simple just described
by energy analogies and mathematics ? [Leanne, Sheila, Nick]
Yup - you really just start with a string and then see how the math
lets the strings wiggle. Unlike a musical instrument's vibrations
(which are very tangible - you can actually watch the string wiggling),
some of the wiggling is very mathematically abstract - in fact these
different types of abstract wiggles correspond to the different string
theories.
9. a) With regard to supersymmetry, what is it that makes the
particle's "partners" so heavy ? And...
We wish we knew! This is one of the biggest problems of modern
physics. There are a wide variety of theories to explain this, but so
far there is nothing definite.
9. b) If these shadow particles are proposed to be so "heavy", it
seems
counter intuitive that they are also hard to see - why is it that
they are hard to see ? [Leanne, Shelia, Nick]
Well whenever a particle is heavy it means you have to put lots of
energy into the accelerator to see it. So it appears that the
superpartners are heavy enough that no accelerator has yet seen one.
But hopefully that will change in the near future...
When you talk about finding the super partners and you say that hopefully we will find them in the near future, are you referring to the current developement at CERN Switzerland? Or what research is being done to look for these particles?
Posted by: Sheila Sweeney | May 31, 2005 at 04:35 PM
Yes this is the Large Hadron Collider at CERN.
There is also discussion about a next generation
collider.
Posted by: Jochen Weller | June 08, 2005 at 02:58 PM
Where in the universe can you get lighter or heavier,like on the Moon
Posted by: Sophie Pallott | December 11, 2005 at 05:50 AM