Now on Nova
Take a thrill ride into a world stranger than science fiction where you play the game by breaking some rules
 
Where a new view of the universe pushes you beyond the limits of your wildest imagination
 
this is the world of string theory a
 
Way of describing every force and all matter from an atom to earth to the end of the galaxies
from the birth of time to its final tick in a single theory a
 
theory of everything
Our guide to this brave new world is Brian Greene the
Best-selling author and physicist and no matter how many times I come here. I never seem to get used to it
Can he help us solve the greatest puzzle of modern physics
That our understanding of the universe is based on two sets of laws that don't agree
Resolving that contradiction eluded even Einstein who made it his final quest
After decades, we may finally be on the verge of a breakthrough
The solution is strings tiny
bits of energy vibrating like the strings on a cello a cosmic
symphony at the heart of all reality
But it comes at a price
Parallel universes and 11 dimensions most of which you've never seen
We really may live in a universe with more dimensions than meet the eye
people who've said that there are extra dimensions of space have been labeled crackpots or people who are bananas a
mirage of Science and Mathematics or the ultimate
theory of everything the string theory fails to provide the testable prediction then
Nobody should believe it. Is that a theory of physics or a philosophy?
one thing that is certain is that string theory is already showing us that the universe may be a lot stranger than
Any of us ever imagined?
Coming up tonight
we
accidentally discovered string theory the humble beginnings of a revolutionary idea
I was completely convinced it was going to say Susskind is the next Einstein
This seemed crazy to people I was depressed I was unhappy the result was I went home to get drunk
obsession drive scientists to pursue the holy grail of physics
But are they ready? From what they discover step into the bizarre world the elegant universe right now?
Major funding for Nova is provided by the following
It's a little-known secret
But for more than half a century a dark cloud has been looming over modern science
Here's the problem our understanding of the universe is based on two
Separate theories one is Einstein's general theory of relativity
That's a way of understanding the biggest things in the universe things like stars and galaxies
But the littlest things in the universe
Atoms and subatomic particles play by an entirely different set of rules
called quantum mechanics
These two sets of rules are each incredibly accurate in their own domain
But whenever we try to combine them to solve some of the deepest mysteries in the universe
disaster strikes
Take the beginning of the universe the Big Bang
At that instant a tiny nugget erupted violently
Over the next 14 billion years the universe
Expanded and cooled into the stars
galaxies and planets
We see today
But if we run the cosmic film in Reverse everything that's now rushing apart comes back together
So the universe gets smaller hotter and denser as we head back to the beginning of time as
we reach the Big Bang when the universe was both enormous, ly heavy and
Incredibly tiny our projector jams
Our two laws of physics when combined break down
But what if we could unite quantum mechanics and general relativity and see the cosmic film in its entirety
Well a new set of ideas called string theory may be able to do that
And if it's right, it would be one of the biggest blockbusters in the history of science
Someday string theory may be able to explain all of nature from the tiniest bits of matter
to the farthest reaches of the cosmos
Using just one single ingredient tiny vibrating strands of energy called strings
But why do we have to rewrite the laws of physics to accomplish this
Why does it matter the two law that we have are incompatible?
Well, you can think of it like this
imagine you lived in a city ruled not by one set of traffic laws, but by two
Separate sets of laws that conflicted with each other as you can see
It would be pretty confusing
To understand this place you'd need to find a way to put these two conflicting sets of laws together into an all-encompassing
Set that makes sense
We work on the assumption that there is a theory out there and it's our job
We're sufficiently smart and sufficiently industrious to figure out what it is
We don't have a guarantee. It isn't written in the stars that we're going to succeed
but in the end
We hope we will have a single theory that governs everything
But before we can find that theory we need to take a
Fantastic journey to see why the two sets of laws we have
conflict with each other and
the first stop on this strange trip is
the realm of very large objects
To describe the universe on large scales we use one set of laws
Einstein's general theory of relativity and that's a theory of how gravity works
general relativity
pictures space as sort of like a
Trampoline a smooth fabric that heavy objects like stars and planets
Can warp and stretch?
Now according to the theory these warps and curves create what we feel as gravity
That is the gravitational pull that keeps the earth in orbit around the Sun is really nothing more than our planet
Following the curves and contours that the Sun creates in the spatial fabric
But the smooth gently curving image of space
Predicted by the laws of general relativity is not the whole story
To understand the universe on extremely small scales
We have to use our other set of laws quantum mechanics and as we'll see quantum mechanics paints a picture of space
So drastically different from general relativity
That you think they were describing two completely separate universes
To see the conflict between general relativity and quantum mechanics
We need to shrink way way way down in size
And
as we leave the world of large objects behind
And approach the microscopic realm a familiar picture of space in which everything behaves predictably
Begins to be replaced by a world with a structure that is far less certain
and
If we keep shrinking
Getting billions and billions of times smaller than even the tiniest bits of matter
Atoms and the tiny particles inside of them the laws of the very small
Quantum mechanics say that the fabric of space becomes bumpy and chaotic
Eventually, we reach a world so turbulent that it defies common sense
down here space and time are so twisted and distorted that the conventional ideas of
left and right
Up and down
Even before and after break down
There's no way to tell for certain that I'm here or here or
Maybe I arrived here before I arrived here
In the quantum world, you just can't pin everything down. It's an inherently wild and frenetic place
The laws in the quantum world are very different from the laws that we are used to
And is that surprising why should the worlds of the very small at an atomic level?
why should that world obey the same kind of rules and laws that we are used to in our world with snapples and oranges and
Walking around on the street. Why would it will behave the same way?
the fluctuating jittery picture of space and time predicted by quantum
Mechanics is in direct conflict with the smooth
orderly
geometric model of space and time
described by general relativity
But we think that everything from the frantic dance of subatomic particles
to the majestic swirl of galaxies
Should be explained by just one grand physical principle one master equation
If we can find that equation how the universe really works at every time and place
Will at last be revealed
You see what we need is a theory that can cope with the very tiny and the very massive
One that embraces both quantum mechanics and general relativity and never break down
ever
For physicists finding a theory that unites general relativity and quantum
Mechanics is the Holy Grail because that framework would give us a single
mathematical theory that describes all the forces that rule our universe
general relativity describes the most familiar of those forces
gravity
But quantum mechanics describes three other forces the strong nuclear force
That's responsible for gluing protons and neutrons together inside of atoms
Electromagnetism
Which produces light electricity and magnetic attraction and the weak nuclear force
That's the force responsible for radioactive decay
Every event in the universe from the splitting of an atom
to the birth of a star is
Nothing more than these four forces
interacting with matter
Albert Einstein spent the last 30 years of his life
searching for a way to describe the forces of nature in a single theory and
Now string theory may fulfill his dream of unification
for centuries
scientists have pictured the fundamental ingredients of nature atoms and the smaller particles inside of them as
tiny balls or points
But string theory proclaims that at the heart of every bit of matter is a tiny
vibrating strands of energy called
a string and
a new breed of scientist believes these minuscule strings are the key to uniting the world of the large and
the world of the small in a single theory
The idea that a scientific theory that we already have in our hands could answer the most basic questions is extremely seductive
For about two thousand years
All of our physics essentially has been based on essentially. We were talking about billiard balls
the a very idea of the string is such a paradigm shift because
Instead of billiard balls you have to use little strands of spaghetti
But not everyone is enamored of this new theory
So far no experiment has been devised that can prove these tiny strings exist
Let me put it bluntly there are physicists and there are string theorists. It is a new
Discipline a new you may call it tumor. You can call it what you will
They have focused on questions which experiment cannot address
They will deny that these string theorists, but it's a kind of physics, which is not yet testable
It does not make predictions that have anything to do with experiments that can be done in the laboratory or with observations
That could be made in space or from telescopes
Yes, I was brought up to believe and I still believe that physics is an experimental science it deals with the results two
experiments or in the case of astronomy observations
From the start many scientists thought string through is simply too far out and
frankly
the strange way the theory evolved in a series of twists turns and
Accidents only made it seem more unlikely. In fact, even its birth has been turned into something of a myth which goes like this
In
the late 1960s the young Italian physicist named Gabriele Veneziano
was searching for a set of equations that would explain the strong nuclear force the
extremely powerful glue that holds the nucleus of every atom together binding
protons to neutrons
As
the story goes he happened on a dusty book on the history of mathematics and
In it, he found a 200 year old equation first written down by a Swiss mathematician
Leonhard Euler
Vinet Siana was amazed to discover that Euler's equations long thought to be nothing more than a mathematical curiosity
Seemed to describe the strong force
He quickly published a paper and was famous ever after for this accidental discovery. I
See occasionally written in books that
that this
model was invented by chance or was found in a math book and
This makes me feel pretty bad
What is true is that
The function was the outcome of the long year of work
and
We accidentally discovered string theory
However, it was discovered boilers equation which miraculously
explained the strong force took on a life of its own this
Was the birth of string theory
Passed from colleague to colleague
Euler's equation ended up on the chalkboard in front of a young American physicist Leonard Susskind
To this day. I remember the formula the formula
Was
And I looked at it and I said, you know, this is so simple even I can figure out what this is
Susskind retreated to his attic to investigate
He understood that this ancient formula
described the strong force mathematically but beneath the abstract symbols, it caught a glimpse of something new I
Fiddled with it I monkeyed with it. I sent my attic I think for two months on and off
But the first thing I have seen it it was describing some kind of particles
Which had internal structure which could vibrate?
which could do things which wasn't just a point particle and I began to realize what was being described here was a string an
Elastic string like a rubber band or like a rubberband cut in half and this rubber bands could not only stretch and contract
but wiggle and
Marvel of marvels it exactly agreed with his formula
I was pretty sure at that time that I was the only one in the world who knew this
Susskind wrote up his discovery introducing the revolutionary
idea of strings
But before his paper could be published. It had to be reviewed by a panel of experts
I was completely convinced that when it came back it was going to say
Susskind is the next Einstein or maybe even the next Newton and it came back saying yeah
This paper is not very good. Probably shouldn't be published. I was truly knocked off my chair. I was depressed
I was unhappy I was saddened by it. It made me a nervous wreck and
The result was I went home and got drunk
As Susskind drowned his sorrows over the rejection of his far-out idea
It appeared string theory was dead
Meanwhile mainstream science was embracing particles as points not strings
for decades physicists had been exploring the behavior of
microscopic particles by smashing them together at high speeds and
studying those collisions in
The showers of particles produced they were discovering that nature is far richer than they thought
Once a month, they'd be a discovery of a new particle
The Roma's on the Omega particle would be particle B one particle B two particle Phi Omega
More letters were used than exist in most alphabets. It was a population explosion of particles
It was a time when graduate students would run through the halls of a physic building say they discovered another
Particle and it fit the theories and it was also exciting
and
in this zoo of new particles
Scientists weren't just discovering building blocks of matter
Leaving string theory in the dust
physicists made a startling and strange prediction
That the forces of nature can also be explained by particles
Now this is a really weird idea but it's kind of like a game of catch in which the players like me and
me are particles of matter and
The ball we're throwing back and forth is a particle of force
It's called a messenger particle
For example in the case of magnetism the electromagnetic force
This ball would be a photon. The more of these messenger particles are photons that are exchanged between us
the stronger the magnetic attraction
and
Scientists predicted that it's this exchange of messenger particles that creates what we feel as force
Experiments confirm these predictions with the discovery of the messenger particles for electromagnetism
the strong force and the weak force and
Using these newly discovered particles
Scientists are closing in on Einsteins dream of unifying the forces
Particle physicists reasoned that if we rewind the cosmic film to the moments in just after the Big Bang
Some 14 billion years ago when the universe was trillions of degrees hotter the messenger particles for electromagnetism
And the weak force would have been
indistinguishable
Just as cubes of ice melt into water in the hot Sun
experiments show that as we rewind
To the extremely hot conditions of the Big Bang the weak and electromagnetic
Forces meld together and unite into a single force called the electroweak
and
Physicists believe that if you roll the cosmic film back even further
The electroweak would unite with the strong force in one Grand super force
Although that has yet to be proven
Quantum mechanics was able to explain how three of the forces operate on the subatomic level
All of a sudden we had a
consistent theory of elementary particle physics, which allows us to describe all of the
Interactions weak strong electromagnetic in the same language it all
made sense and
It's all in the textbooks
everything was converging toward a simple picture of the known particles and forces a picture which eventually became known as
The standard model. I think I gave it that name
Professor Sheldon Glashow Abdul, Salam and Steven Weinberg
The inventors of the standard model both the name and the theory were the toasts of the scientific community
receiving nobel prize after nobel prize
But behind the fanfare was a glaring omission
Although the standard model explained three of the forces that ruled the world of the very small
It did not include the most familiar force
Gravity
Overshadowed by the standard model
String theory became a backwater of physics
Most people in our community lost completely
Interest in string theory they said okay. That was a very nice elegant thing but had nothing to do with nature
It's not taken seriously and by much of the community
but
the early pioneers of string theory are convinced that
They can smell reality and continue to pursue the idea
But the more these diehards delved into string theory the more problems they found
Early string theory had a number of problems one was that it predicted a particle, which we know is unphysical
It's what's called a tachyon a particle that travels faster than light. There was this discovery that the theory requires ten dimensions
which is
Very disturbing, of course, this is obvious. But that's more than there are
It had the massless
Particle, which was not seen experiments. So these theories didn't seem to make sense
This is seemed crazy to people basically string theory was not getting off the ground
People threw up their hands and said this can't be right
By 1973
Only a few young physicists were still wrestling with the Obscure equations of string theory
One was John Schwarz who was busy tackling string theories numerous problems
among them a mysterious massless particle predicted by the theory but never seen in nature and an
assortment of anomalies or
mathematical inconsistencies
We spent a long time trying to fiddle with a theory we tried all sorts of ways of making
the dimension before
Getting rid of these massless particles the tachyons and so on but it was always ugly and unconvincing
for four years Schwarz tried to tame the unruly
equations of string theory
changing
adjusting
Combining and recombining them in different ways
But nothing worked on
The verge of abandoning string theory Schwarz had a brainstorm
Perhaps his equations were describing gravity
But that meant reconsidering the size of these tiny strands of energy
We weren't thinking about gravity up till that point
but as soon as we
Suggested that maybe we should be dealing with a theory of gravity
We had to radically change our view of how big these strings were
By supposing that strings were a hundred billion billion times smaller than an atom
One of the theories vices became a virtue
The mysterious particle John Schwarz had been trying to get rid of now appeared to be a graviton
The long sought after particle believed to transmit gravity at the quantum level
String theory had produced the piece of the puzzle missing from the standard model
Schwartz submitted for publication his groundbreaking new theory describing how gravity works in the subatomic world
It seemed very obvious to us that it was right
But there was really no reaction in the community whatsoever
Once again string theory fell on deaf ears, but
Schwartz would not be deterred
He had glimpsed the Holy Grail
If strings described gravity at the quantum level
They must be the key to unifying the four forces
He was joined in this quest by one of the only other scientists willing to risk his career on strings
Michael Greene in a sense. I think that we had a quiet confidence that the string theory is obviously, correct
And it didn't matter much if people didn't see it at that point. They would see it down line
But for greens confidence to pay off
He and Schwartz would have to confront the fact that in the early
1980s string theory still had fatal flaws in the math known as anomalies and
Anomaly is just what it sounds like. It's something that's strange or out of place something. That doesn't belong
Now this kind of anomaly is just weird
But mathematical anomalies can spell doom for a theory of physics they're a little complicated. So here's a simple example
Let's say we have a theory in which these two equations
Describe one physical property of our universe now if I solve this equation over here
And I find x equals 1 and if I solve this equation over here and find x equals 2
I know my theory has anomalies because there should only be one value for X
Unless I can revise my equations to get the same value for x on both sides. The theory is dead
in the early 1980s string theory was riddled with
Mathematical anomalies kind of like these although the equations were much more complex
The future of the theory depended on ridding the equations of these fatal inconsistencies
After Schwartz and Greene battled the anomalies and string theory for five years their work
culminated late one night in the summer of
1984
It was widely believed that these theories must be inconsistent
because of anomalies
well for no really good reason, I just felt that had to be wrong because I
Felt the strength. Oh, he's got to be right there further can't beat anomalies
So he's decided we got to calculate these things
Amazingly it all boiled down to a single calculation
on
one side of the blackboard they got
496 and
If they got the matching number on the other side
It would prove string theory was free of anomalies
I do remember
a particular
moment when John Schwarz and I were talking at the blackboard and working out these numbers which had to fit and they just had to
Match exactly. I
remember joking with John Schwarz at that moment because
There was thunder and lightning there's a big amount in the storm in a span of a permit
And I remember saying something like no, but we must be getting pretty close because the gods are trying to prevent us
Completing this calculation and indeed they did match
The matching numbers meant the theory was free of anomalies
And it had the mathematical depth to encompass all four forces
So we recognize that only that the strings could describe gravity but they could also describe the other forces
So we spoke in terms of unification
and we saw this as the possibility of
Realizing the dream that Einstein had expressed in his later years of unifying the different forces and some deeper framework
We felt with the game. That was an extraordinary
Moment
Because we realized that
No other Theory had ever succeeded in doing that, but by now it's like crying wolf each time. We've done something, right?
Everyone's gonna be excited they weren't so I feel by now. I didn't expect much of a reaction
But this time the reaction was explosive in less than a year the number of string
Theorists left from just a handful to hundreds up to that moment the longest talk
I'd ever given on the subject was five minutes at some minor conference and then suddenly I wasn't
Invited all over the world to give talks and lectures and so forth
String theory was christened the theory of everything
In early fall of 1984 I came here to Oxford University
to begin my graduate studies in physics
Some weeks after I saw a poster for a lecture by Michael Greene, I
Didn't know who he was
But then again, I really didn't know who anybody was but the title of the lecture was something like the theory of everything
So, how could I resist?
This elegant new version of string theory seemed capable of describing all the building blocks of nature
Here's how
Inside every grain of sand
Our billions of tiny atoms
Every atom is made of smaller bits of matter
electrons orbiting a nucleus made of protons and neutrons which
are made of even smaller bits of matter called quarks, but
String theory says this is not the end of the line
It makes the astounding claim that the particles making up everything in the universe are made of even smaller
Ingredients tiny wiggling strands of energy that look like strings
Each of these strings is unimaginably small
in fact, if an atom were enlarged to the size of the solar system a
String would only be as large as a tree and
Here's the key idea
Just as different vibrational patterns or frequencies of a single cello string
Create what we hear as different musical notes
The different ways that strings vibrate give particles their unique properties
Such as mass and charge
For example
The only difference between the particles making up you and me and the particles that transmit gravity and the other forces
Is the way these tiny strings vibrate?
Composed of an enormous number of these oscillating strings
the universe can be thought of as a grand cosmic symphony and
this elegant idea
resolves the conflict between our jittery
Unpredictable picture of space on the subatomic scale and our smooth picture of space on the large scale
And as the jitteriness of quantum theory versus the gentleness of Einstein's general theory of relativity
That makes it so hard to bridge the tube to stitch them together
Now what string theory does it comes along and basically calms the jitters of quantum mechanics
It spreads them out by virtue of taking the old idea of a point particle and spreading it out into a string
So the jittery behaviors there, but it's just
Sufficiently less violent that quantum theory and generality stitched together perfectly within this framework
It's a triumph of mathematics with nothing but these tiny
vibrating strands of energy
String theorists claim to be fulfilling Einsteins dream of uniting all forces and all matter
But this radical new theory contains a chink in its armor
No experiment can ever check up what's going on at the distances that are being studied?
No
observation can relate to these tiny distances or high energies that is to say
there ain't no experiment that could be done nor is there any
Observation that could be made that would say you guys are wrong
The theory is safe
permanently safe
Is that a theory of physics or a philosophy I ask you
people often criticize string theory for saying that it's very far removed from any direct experimental test, and it's
surely is not very young a bunch of physics for that reason and
I my response to that is simply that they're going to be proved wrong
Making string theory even harder to prove is that in order to work the complex?
Equations require something that sounds like it's straight out of science fiction
extra dimensions of space
We've always thought for
Centuries that there was only what we can see, you know this dimension that one and another one
there's only three dimensions of space and one of time and
People who've said that there are extra dimensions of space have been labeled as you know, crackpots or people who are bananas
Well string theory really predicts it
To be taken seriously string theorists had to explain how this bizarre
Prediction could be true and they claim that the far out idea of extra dimensions may be more down to earth
than you think
Let me show you what I mean
I'm off to see a guy who was one of the first people to think about this strange idea
I'm supposed to meet him at four o'clock at his apartment on Fifth Avenue and 93rd Street on the second floor
Now in order to get to this meeting I need four pieces of information
One for each of the three dimensions of space a street and Avenue and a floor number and one more for time the fourth dimension
You can think about these as the four dimensions of common experience
left-right back-forth
Up-down and time as
It turns out the strange idea that there are additional dimensions stretches back almost a century
Our sense that we live in a universe of three spatial dimensions really seems beyond question
but in 1919 Theodor Kaluza a virtually unknown German mathematician
Had the courage to challenge the obvious
He suggested that maybe just maybe our universe has one more dimension
That for some reason we just can't see
Look, he says here. I like your idea. So why does he delay?
you see Colusa had sent his idea about an additional spatial dimension to Albert Einstein and
Although Einstein was initially enthusiastic
He then seemed to waver and for two years held up publication of klutzes paper
Eventually kaluza's paper was published after Einstein decided extra dimensions were his cup of tea
Here's the idea in
1916 Einstein show that gravity is nothing but warps and ripples in the four familiar dimensions of space and time
just
three years later
Kaluza proposed that electromagnetism might also be ripples
but for that to be true Colusa needed a place for those ripples to occur, so
Kaluza proposed an additional
hidden dimension of space
But if Colusa was right, where is this extra dimension and what would extra dimensions look like?
Can we even begin to imagine them? Well building upon kaluza's work the swedish physicist oskar klein
suggested an unusual answer
Take a look at the cables supporting that traffic light from this far away. I can't see that they have any thickness
Each one looks like a line something with only a single dimension
but suppose we could explore one of these cables way up close like from the point of view of an ant
Now a second dimension which wraps around the cable becomes visible?
From its point of view the ant can move forwards and backwards and it can also move clockwise and counterclockwise
So
Dimensions can come in two varieties. They can be long and unfurled like the length of the cable
But they can also be tiny and curled up like the circular direction that wraps around it
pollutes in climate the wild suggestion that the fabric of our universe
Might be kind of like the surface of the cable having both big extended dimensions the three that we know about
But also tiny curled up dimensions
curled up so tiny billions of times more than even a single atom that we just can't see them and
So our perception that we live in a universe with three spatial dimensions
May not be correct after all we really may live in a universe with more dimensions
Than meet the eye
So, what would these extra dimensions look like
Kaluza and Klein proposed that if we could shrink down billions of times we'd find one
extra tiny curled up dimension located at every point in space and
Just the way an ant can explore the circular dimension that wraps around a traffic light Cable in
Theory an ant that is billions of times smaller
Could also explore this tiny curled up circular dimension
This idea that extra dimensions exist all around us lies at the heart of string theory in
Fact the mathematics of string theory demand not one but six extra dimensions
Twisted and curled into complex little shapes that might look something like this
If string theory is right we would have to admit that there are anymore dimensions out there and I find that completely mind-blowing
If I take the theories we haven't now literally I would conclude that the extra dimensions really exist they're part of nature
When we talk about extra dimensions
We literally mean extra dimensions of space
that are the same as the dimensions of space that we see around us and
The only difference between them has to do with their shape
But how could these tiny extra?
Dimensions curled up into such peculiar shapes have any effect on our everyday world
Well, according to string theory shape is everything
Because of its shape a French horn can produce dozens of different notes
When you press one of the keys
You change the note because you change the shape of the space inside the horn where the air resonates
And we think the curled up spatial dimensions in string theory work in a similar way
If we could shrink down small enough to fly into one of these tiny six dimensional shapes predicted by string theory
We would see how the extra dimensions are twisted and curled back on each other
influencing how strings the fundamental ingredients of our universe move and vibrate
and
This could be the key to solving one of nature's most profound mysteries
You see our universe is kind of like a finely tuned machine
Scientists have found that they're about twenty numbers
Twenty fundamental constants of nature that give the universe two characteristics we see today
These are numbers like how much in electron weighs
the strength of gravity the electromagnetic force and the strong and weak forces
Now as long as we set the dials on our universe machine to precisely the right values for each of these 20 numbers
The machine produces the universe we know and love
But if we change the numbers by adjusting the settings on this machine even a little bit the consequences are dramatic
For example if I increase the strength of the electromagnetic force
Atoms repel one another more strongly so the nuclear furnaces that make Starshine break down
the stars including our Sun fizzle out and
The universe as we know it disappears
So what exactly in nature sets the values of these 20 constants so precisely
Well, the answer could be the extra dimensions in string theory
That is the tiny curled up six dimensional shapes predicted by the theory
cause one string to vibrate and precisely the right way to produce what we see as a photon and
Another string to vibrate in a different way producing an electron
So
according to string theory these minuscule extra dimensional shapes
Really may determine all the constants of nature
Keeping the cosmic symphony of strings in tune
By the mid-1980s string theory look hon stoppable
But behind the scenes the theory wasn't angles
Over the years string theorists had been so successful that they had constructed not one
But five different versions of the theory
Each was built on strings and extra dimensions, but in detail the five theories were not in harmony
in
Some versions strings were open-ended strands in
Others they were closed loops
At first glance a couple of versions even required 26 dimensions
All five versions appeared equally valid, but which one was describing our universe?
This was kind of an embarrassment for string theorists because on the one hand we wanted to say that this might be it the final
description of the universe
But then in the next breath we had to say and it comes in five flavors five variations
Now there's one universe you expect there to be one theory not five. So this is an example where more is definitely less
One attitude that people who didn't like string theory could take was well you have five thirty, so it's not unique
This was a peculiar state of affairs
Because we were looking just to describe one theory of nature and not five if there's five of them
Well, maybe there's smart enough people would find twenty of them
Or maybe there's an infinite number of them and you're back to just searching around at random for four theories of the world
maybe one of these five string theories is
Describing our universe on the other hand
Which one and why what are the other ones good for what having five string theories even though it's big progress?
Raises the obvious question. If one of those theories describes our universe the new lives in the other four worlds
String theory seemed to be losing steam once again and
frustrated by a lack of progress many physicists abandoned the field
Will string theory proved to be a theory of everything
Or will it unravel into a theory of nothing?
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