Any infinitesimally small particles?

[Gnomie27]

is there any particle that is infinitely small? is there anything at all that's infinitely small?

i might have been inclined to say a singularity, but last i checked someone "[took] the singularity out of the black hole".

thanks

 

[SteamKing]

Depends on what you mean by 'infinitely small'.

 

[bhobba]

As far as we can tell today all fundamental particles are point particles meaning they have no internal structure or discernible size. String theory predicts however they are not points but strings.

Thanks
Bill

 

[ShayanJ]

If one considers mainstream QM and SM,the answer is yes,all fundamental particles are point-like,infinitely small.And by combining such point particles you can't get a particle with finite size,so I guess composite particles should be considered point-like too.
But if you want to consider other theories too,I can give you some examples that suggest finite sizes for elementary particles.One of them is string theory which says that the particles are in fact vibrating strings which their vibration patterns determine their properties.
Another example is Einstein-Cartan theory,an extension to GR.It requires the fermions to have finite sizes(I don't know the reason).
And...mmmm...back to the QM...considering particles as point-like makes some troubles which are cured by a process called renormalization.Some people don't like it because it doesn't seem so physical to them!Although I remember there was a physical interpretation to it that made things OK but I'm not sure.
Anyway,although mainstream physics is considering elementary particles as point-like,here and there you can find some little clues stating the contrary!

 

[Nugatory]

And by combining such point particles you can't get a particle with finite size,so I guess composite particles should be considered point-like too.

The entire macroscopic world is a counterexample to this non sequitur.

 

[CWatters]

http://www.guardian.co.uk/science/2011/may/25/electrons-round-cosmos

After three months of experiments in a basement laboratory in London, scientists can confirm – with more confidence than ever – that the electron is very, very round

but as for how big it is...

 

[ShayanJ]

The entire macroscopic world is a counterexample to this non sequitur.

No,it is not.Most of the volume of all materials is empty space.Matter exists because of that empty space and various kinds of repulsive forces.In fact a simple analysis will show that the world doesn't need finite sizes for composite particles for its existence

 

[Vanadium 50]

A baseball is a composite particle. It does not have infinitesimal size.

 

[ShayanJ]

A baseball is a composite particle. It does not have infinitesimal size.

A baseball is what I call "matter"...by composite particle I mean protons,neutrons etc...I think I don't have to explain the difference,its just obvious!

 

[Nugatory]

A baseball is what I call "matter"...by composite particle I mean protons,neutrons etc...I think I don't have to explain the difference,its just obvious!

OK, let's look at a proton or a neutron. It clearly has a non-zero size; and it is composed of three point-particle quarks and a bunch of empty space. I'm still seeing a counter-example to your (IMO absurd) claim that a particle composed of point particles must itself be a point particle.

 

[ShayanJ]

OK, let's look at a proton or a neutron. It clearly has a non-zero size; and it is composed of three point-particle quarks and a bunch of empty space. I'm still seeing a counter-example to your (IMO absurd) claim that a particle composed of point particles must itself be a point particle.

Oh...sorry...you know,looks like I wasn't looking at it!
Suddenly it came in front of my eye and I now see I was wrong.
Well,sometimes it happens...temporary foolishness about a particular subject!

 

[WannabeNewton]

Another example is Einstein-Cartan theory,an extension to GR.It requires the fermions to have finite sizes(I don't know the reason).

Connections in Einstein-Cartan theory are not assumed to have vanishing torsion unlike in GR. That is where it comes from.