What is the smallest possible thing in the universe?
Discussion
This looks like it could be an interesting programme on BBC 2 tonight at 9pm... and the BBC news article provides a lot of interesting information to a layman such as myself 
http://www.bbc.co.uk/news/science-environment-1943...
http://www.bbc.co.uk/news/science-environment-1943...
BBC said:
Science's ongoing quest to find the smallest possible things remains tantalisingly incomplete, as physicist Prof Andy Parker explains.
Physics has a problem with small things. Or, to be more precise, with infinitely small things.
We imagine that we can move any distance we like, no matter how small.
This perception was exploited by Zeno in one of his famous paradoxes. Achilles could never actually get anywhere since the distance he would have to cover could be halved an infinite number of times - halfway there, halfway again, and so on. He would have to take an infinite number of ever-smaller steps to reach his goal.
Mathematicians have explained this apparent paradox, and are completely comfortable with infinite numbers, as well as infinitely small distances and objects. Their answers are used in physics to describe the world inside the atom.
But nature is not so comfortable with this. When we try to describe something as a "point" - an infinitely small object, that throws up some of the most intractable problems in physics.
Since all of particle physics relies on "point-like" particles, reacting to forces in tiny spaces, one can anticipate trouble.
This duly appears in the form of nonsense answers when the equations are used at the smallest distances.
Physicists are therefore increasingly suspicious of points, and asking whether in fact Nature has a limit for the smallest possible object, or even whether there is a smallest possible space.
Russian Dolls
The quest for the smallest building blocks of Nature probably stretches back to the first caveman who tried to put a sharp edge on a flint.
The Greeks gave us the concept of billiard-ball shaped atoms which stick together to make up the materials we see, and this picture is still in most peoples' minds today.
Over a century ago, JJ Thomson managed to extract electrons from atoms in Cambridge, and he was followed in 1932 by Cockcroft and Walton, who split the atomic nucleus with a cleverly designed particle accelerator.
These turned out to be only the first Russian Dolls.
Successive experiments, using more and more powerful accelerators, revealed that the nucleus was composed of protons and neutrons, and that they in turn were made of quarks.
The evidence for the Higgs boson recently produced at the Large Hadron Collider at Cern is the latest of these.
But all attempts to split quarks or electrons, even using the awesome power of the LHC have failed.
The basic building blocks seem to be points, certainly smaller than 0.0000000000000000001 metres across.
To infinity
One can see where the problem comes from. All the forces in nature get stronger at short distances.
Newton's famous "inverse-square law" of gravity, for example, says that the force of gravity gets four times stronger if you halve your distance from an object.
If we imagine particles as points, you can make the distance between two of them as small as you like, so the force becomes infinite. Ultimately this would break up the fabric of space, creating a foam of black holes. That would certainly slow Achilles down!
Physicists can normally sidestep this problem, using the fuzziness built into quantum mechanics which allows matter to behave as particles or waves.
You may also have heard of Heisenberg's Uncertainty Principle which does not allow us to know exactly where anything is. So even though a particle might be a point, its location is uncertain, and in the equations it looks like a fuzzy ball - problem solved!
Well almost - we don't actually know how to apply quantum mechanics to gravity, and so we still get stuck with nonsensical predictions such as the complete collapse of space if we try to describe strong gravitational fields, like those inside black holes.
It turns out that quantum mechanics and Einstein's theory of gravity just don't mix.
Various ingenious solutions have been proposed to this problem.
The most obvious is that there is another Russian Doll, and the smallest particles are tiny billiard balls. If so, one day, perhaps with the Hadron Collider, we will see the size of the smallest objects.
But theoretical physicists prefer the idea that the particles are not in fact round, but tiny "strings", like bits of elastic.
They have a finite length, but an infinitely small width. This solves the problem, since you can never be at the same distance from all of the string.
You may have guessed that is what we call String Theory.
Strings can vibrate, and this allows us to explain all of the strange fundamental particles which we see as different vibrations of the strings - different notes from a cosmic violin.
So far, so simple - but to explain the particles we know about, the strings have to vibrate in lots of different ways.
Superstring Theory allows them to vibrate in a bizarre space with 11 dimensions - up, down, sideways, "crossways" and 7 other ways!
Experiments at the LHC are looking for evidence that you can move "crossways". If we can, there could be whole universes, as big and marvellous as our own, sitting just down the road "crossways".
We can go even further - perhaps we should not be looking for the smallest object, but the smallest distance.
If space is composed of lots of small grains, then our problem can be solved, since no two particles can ever be closer together than the size of a grain.
Achilles would move along in a series of small, but finite, steps. By looking at particles travelling over huge distances across the cosmos, we hope to see the accumulated effect of bumping along lots of tiny grains, rather than gliding through the smooth space which we imagine.
In the end, the answers will be found in experiments, not in our imaginations. Perhaps the most amazing thing we have discovered is the scientific method, which allows us to pose and answer questions like "How small is the Universe?". Not bad for slightly evolved cavemen!
Andy Parker is Professor of High Energy Physics at Cambridge University and a founder of the ATLAS experiment for the Large Hadron Collider.
Physics has a problem with small things. Or, to be more precise, with infinitely small things.
We imagine that we can move any distance we like, no matter how small.
This perception was exploited by Zeno in one of his famous paradoxes. Achilles could never actually get anywhere since the distance he would have to cover could be halved an infinite number of times - halfway there, halfway again, and so on. He would have to take an infinite number of ever-smaller steps to reach his goal.
Mathematicians have explained this apparent paradox, and are completely comfortable with infinite numbers, as well as infinitely small distances and objects. Their answers are used in physics to describe the world inside the atom.
But nature is not so comfortable with this. When we try to describe something as a "point" - an infinitely small object, that throws up some of the most intractable problems in physics.
Since all of particle physics relies on "point-like" particles, reacting to forces in tiny spaces, one can anticipate trouble.
This duly appears in the form of nonsense answers when the equations are used at the smallest distances.
Physicists are therefore increasingly suspicious of points, and asking whether in fact Nature has a limit for the smallest possible object, or even whether there is a smallest possible space.
Russian Dolls
The quest for the smallest building blocks of Nature probably stretches back to the first caveman who tried to put a sharp edge on a flint.
The Greeks gave us the concept of billiard-ball shaped atoms which stick together to make up the materials we see, and this picture is still in most peoples' minds today.
Over a century ago, JJ Thomson managed to extract electrons from atoms in Cambridge, and he was followed in 1932 by Cockcroft and Walton, who split the atomic nucleus with a cleverly designed particle accelerator.
These turned out to be only the first Russian Dolls.
Successive experiments, using more and more powerful accelerators, revealed that the nucleus was composed of protons and neutrons, and that they in turn were made of quarks.
The evidence for the Higgs boson recently produced at the Large Hadron Collider at Cern is the latest of these.
But all attempts to split quarks or electrons, even using the awesome power of the LHC have failed.
The basic building blocks seem to be points, certainly smaller than 0.0000000000000000001 metres across.
To infinity
One can see where the problem comes from. All the forces in nature get stronger at short distances.
Newton's famous "inverse-square law" of gravity, for example, says that the force of gravity gets four times stronger if you halve your distance from an object.
If we imagine particles as points, you can make the distance between two of them as small as you like, so the force becomes infinite. Ultimately this would break up the fabric of space, creating a foam of black holes. That would certainly slow Achilles down!
Physicists can normally sidestep this problem, using the fuzziness built into quantum mechanics which allows matter to behave as particles or waves.
You may also have heard of Heisenberg's Uncertainty Principle which does not allow us to know exactly where anything is. So even though a particle might be a point, its location is uncertain, and in the equations it looks like a fuzzy ball - problem solved!
Well almost - we don't actually know how to apply quantum mechanics to gravity, and so we still get stuck with nonsensical predictions such as the complete collapse of space if we try to describe strong gravitational fields, like those inside black holes.
It turns out that quantum mechanics and Einstein's theory of gravity just don't mix.
Various ingenious solutions have been proposed to this problem.
The most obvious is that there is another Russian Doll, and the smallest particles are tiny billiard balls. If so, one day, perhaps with the Hadron Collider, we will see the size of the smallest objects.
But theoretical physicists prefer the idea that the particles are not in fact round, but tiny "strings", like bits of elastic.
They have a finite length, but an infinitely small width. This solves the problem, since you can never be at the same distance from all of the string.
You may have guessed that is what we call String Theory.
Strings can vibrate, and this allows us to explain all of the strange fundamental particles which we see as different vibrations of the strings - different notes from a cosmic violin.
So far, so simple - but to explain the particles we know about, the strings have to vibrate in lots of different ways.
Superstring Theory allows them to vibrate in a bizarre space with 11 dimensions - up, down, sideways, "crossways" and 7 other ways!
Experiments at the LHC are looking for evidence that you can move "crossways". If we can, there could be whole universes, as big and marvellous as our own, sitting just down the road "crossways".
We can go even further - perhaps we should not be looking for the smallest object, but the smallest distance.
If space is composed of lots of small grains, then our problem can be solved, since no two particles can ever be closer together than the size of a grain.
Achilles would move along in a series of small, but finite, steps. By looking at particles travelling over huge distances across the cosmos, we hope to see the accumulated effect of bumping along lots of tiny grains, rather than gliding through the smooth space which we imagine.
In the end, the answers will be found in experiments, not in our imaginations. Perhaps the most amazing thing we have discovered is the scientific method, which allows us to pose and answer questions like "How small is the Universe?". Not bad for slightly evolved cavemen!
Andy Parker is Professor of High Energy Physics at Cambridge University and a founder of the ATLAS experiment for the Large Hadron Collider.
Mr Gearchange said:
A grain of sand.
As any fule know there are more grains of sand on a beach than there are atoms in the universe.
There are estimated to be approx. 7.5 x 10^18 grains of sand in the world.As any fule know there are more grains of sand on a beach than there are atoms in the universe.
There are close to 10^80 atoms in the observable Cosmos.
Who's Any Fule? He needs to go back to school.
MiseryStreak said:
I love the "Minecraft World" and "Total Human Height" stats. 
Really interesting programme, i really enjoyed the section about the planck length and the bit about the MAGIC telescope with photons of different energies arriving at different times, and the potential impact of light not being a constant.
This makes me want to go back to school and understand the mathematics and symbols behind it all
This makes me want to go back to school and understand the mathematics and symbols behind it all
Are you talking about the Neutrino experiment that was found to show them arriving faster than light and was shown to be wrong or the looking at 7 billion year old gamma ray bursts and seeing a 5 second difference between photons arriving from it with the implication space time is not smooth?
A University of Central Florida research team has created the world's shortest laser pulse and in the process may have given scientists a new tool to watch quantum mechanics in action – something that has been hidden from view until now. UCF Professor Zenghu Chang from the Department of Physics and the College of Optics and Photonics, led the effort that generated a 67-attosecond pulse of extreme ultraviolet light.
An attosecond is an incomprehensible quintillionith of a second. In other words it would take 15 million billion pulses of the size Chang's team achieved to equal one second.
Dr. Chang's success in making ever-shorter light pulses helps open a new door to a previously hidden world, where we can watch electrons move in atoms and molecules, and follow chemical reactions as they take place, "It is astounding to imagine that we may now be able to watch quantum mechanics in process."
Hard to get mind round how short a pulse it is! The last photon to leave the laser would trail the first by only the thickness of a cell wall membrane
Read more at:http://phys.org/news/2012-09-attosecond-extreme-ultraviolet-laser-pulse.html
An attosecond is an incomprehensible quintillionith of a second. In other words it would take 15 million billion pulses of the size Chang's team achieved to equal one second.
Dr. Chang's success in making ever-shorter light pulses helps open a new door to a previously hidden world, where we can watch electrons move in atoms and molecules, and follow chemical reactions as they take place, "It is astounding to imagine that we may now be able to watch quantum mechanics in process."
Hard to get mind round how short a pulse it is! The last photon to leave the laser would trail the first by only the thickness of a cell wall membrane
Read more at:http://phys.org/news/2012-09-attosecond-extreme-ultraviolet-laser-pulse.html
The latter. Neutrinos have never been observed to travel faster than light.
In March 2012, the collocated ICARUS experiment reported neutrino velocities consistent with the speed of light in the same short-pulse beam OPERA had measured in November 2011. ICARUS used a partly different timing system from OPERA and measured seven different neutrinos.[6] In addition, the Gran Sasso experiments BOREXINO, ICARUS, LVD and OPERA all measured neutrino velocity with a short-pulsed beam in May, and obtained agreement with the speed of light.[7]
On June 8, 2012 CERN research director Sergio Bertolucci declared on behalf of the four Gran Sasso teams, including OPERA, that the speed of neutrinos is consistent with that of light. The press release, made from the 25th International Conference on Neutrino Physics and Astrophysics in Kyoto, states that the original OPERA results were wrong, due to equipment failures.[8]
On July 12, 2012 OPERA updated their paper by including the new sources of errors in their calculations. They found agreement of neutrino speed with the speed of light.[9]
http://en.wikipedia.org/wiki/Faster-than-light_neu...
http://arxiv.org/abs/1109.4897
I've been reading about spinons, holons and orbitons (touched on briefly in the Horizons program), even though they are not classified as fundamental particles but instead quasiparticles (not exactly sure why), I think they are candidates nonetheless for the 'smallest things in the universe'.
A fundamental fermion's mass is often described as being inversely proportional to its size, so a top quark (being the heaviest) is the smallest of the fermions. But this is abstract as all of these particles are considered point like so the 'size' isn't as easy to define as in the macrocosm, but in quantum mechanics the particles or 'wave packets' do occupy nonzero volumes.
The electron neutrino is the lightest and often described as the smallest particle in existence but The tau is the heaviest of the leptons so that could be considered to the the smallest.
What size does the Higgs boson have? It has a mass of 126GeV/c^2, which is pretty massive so being a boson could it be smaller than the top quark and the electron neutrino?
Then you have the unobserved bosons (that might not exist), the Graviton, gauge boson mediator of the gravitational field, and the Inflaton, hypothetical mediator of the Inflation of the cosmos.
With all of these dimensionless particles, that's size can be imagined by their collisional cross section, it all depends what force you are using to measure the collisional cross section. So it becomes impossible to answer the question succinctly.
Then there of course gravitational singularities, which by definition have zero volume.
At the moment I think the smallest 'thing' that can be defined to have a diameter in terms of the three extended spatial dimensions and can be directly observed is a Helium Atom. Nothing else exists on its own for long enough to be measured directly. I could be wrong on this though.
In March 2012, the collocated ICARUS experiment reported neutrino velocities consistent with the speed of light in the same short-pulse beam OPERA had measured in November 2011. ICARUS used a partly different timing system from OPERA and measured seven different neutrinos.[6] In addition, the Gran Sasso experiments BOREXINO, ICARUS, LVD and OPERA all measured neutrino velocity with a short-pulsed beam in May, and obtained agreement with the speed of light.[7]
On June 8, 2012 CERN research director Sergio Bertolucci declared on behalf of the four Gran Sasso teams, including OPERA, that the speed of neutrinos is consistent with that of light. The press release, made from the 25th International Conference on Neutrino Physics and Astrophysics in Kyoto, states that the original OPERA results were wrong, due to equipment failures.[8]
On July 12, 2012 OPERA updated their paper by including the new sources of errors in their calculations. They found agreement of neutrino speed with the speed of light.[9]
http://en.wikipedia.org/wiki/Faster-than-light_neu...
http://arxiv.org/abs/1109.4897
I've been reading about spinons, holons and orbitons (touched on briefly in the Horizons program), even though they are not classified as fundamental particles but instead quasiparticles (not exactly sure why), I think they are candidates nonetheless for the 'smallest things in the universe'.
A fundamental fermion's mass is often described as being inversely proportional to its size, so a top quark (being the heaviest) is the smallest of the fermions. But this is abstract as all of these particles are considered point like so the 'size' isn't as easy to define as in the macrocosm, but in quantum mechanics the particles or 'wave packets' do occupy nonzero volumes.
The electron neutrino is the lightest and often described as the smallest particle in existence but The tau is the heaviest of the leptons so that could be considered to the the smallest.
What size does the Higgs boson have? It has a mass of 126GeV/c^2, which is pretty massive so being a boson could it be smaller than the top quark and the electron neutrino?
Then you have the unobserved bosons (that might not exist), the Graviton, gauge boson mediator of the gravitational field, and the Inflaton, hypothetical mediator of the Inflation of the cosmos.
With all of these dimensionless particles, that's size can be imagined by their collisional cross section, it all depends what force you are using to measure the collisional cross section. So it becomes impossible to answer the question succinctly.
Then there of course gravitational singularities, which by definition have zero volume.
At the moment I think the smallest 'thing' that can be defined to have a diameter in terms of the three extended spatial dimensions and can be directly observed is a Helium Atom. Nothing else exists on its own for long enough to be measured directly. I could be wrong on this though.
Gassing Station | Science! | Top of Page | What's New | My Stuff