<s>
In	O
physics	O
the	O
term	O
exchange	B-General_Concept
force	I-General_Concept
has	O
been	O
used	O
to	O
describe	O
two	O
distinct	O
concepts	O
which	O
should	O
not	O
be	O
confused	O
.	O
</s>
<s>
The	O
preferred	O
meaning	O
of	O
exchange	B-General_Concept
force	I-General_Concept
is	O
in	O
particle	O
physics	O
,	O
where	O
it	O
denotes	O
a	O
force	O
produced	O
by	O
the	O
exchange	O
of	O
force	O
carrier	O
particles	O
,	O
such	O
as	O
the	O
electromagnetic	O
force	O
produced	O
by	O
the	O
exchange	O
of	O
photons	B-Application
between	O
electrons	O
and	O
the	O
strong	O
force	O
produced	O
by	O
the	O
exchange	O
of	O
gluons	O
between	O
quarks	B-Operating_System
.	O
</s>
<s>
The	O
idea	O
of	O
an	O
exchange	B-General_Concept
force	I-General_Concept
implies	O
a	O
continual	O
exchange	O
of	O
virtual	O
particles	O
which	O
accompany	O
the	O
interaction	O
and	O
transmit	O
the	O
force	O
,	O
a	O
process	O
that	O
receives	O
its	O
operational	O
justification	O
through	O
the	O
Heisenberg	O
uncertainty	O
principle	O
.	O
</s>
<s>
For	O
instance	O
,	O
electrons	O
and	O
protons	B-Application
have	O
electric	O
charge	O
,	O
so	O
they	O
can	O
produce	O
and	O
absorb	O
the	O
electromagnetic	O
force	O
carrier	O
,	O
the	O
photon	B-Application
.	O
</s>
<s>
Neutrinos	O
,	O
on	O
the	O
other	O
hand	O
,	O
have	O
no	O
electric	O
charge	O
,	O
so	O
they	O
cannot	O
absorb	O
or	O
produce	O
photons	B-Application
.	O
</s>
<s>
Exchange	B-General_Concept
forces	I-General_Concept
were	O
introduced	O
by	O
Werner	O
Heisenberg	O
(	O
1932	O
)	O
and	O
Ettore	O
Majorana	O
(	O
1933	O
)	O
in	O
order	O
to	O
account	O
for	O
the	O
saturation	O
of	O
binding	O
energy	O
and	O
of	O
nuclear	O
density	O
.	O
</s>
<s>
Additionally	O
,	O
Ernst	O
Stueckelberg	O
developed	O
the	O
vector	O
boson	O
exchange	B-General_Concept
force	I-General_Concept
model	O
as	O
the	O
theoretical	O
explanation	O
of	O
the	O
strong	O
nuclear	O
force	O
in	O
1935	O
.	O
</s>
<s>
As	O
another	O
,	O
entirely	O
distinct	O
,	O
meaning	O
of	O
exchange	B-General_Concept
force	I-General_Concept
,	O
it	O
is	O
sometimes	O
used	O
as	O
a	O
synonym	O
for	O
the	O
exchange	B-General_Concept
interaction	I-General_Concept
,	O
between	O
electrons	O
which	O
arises	O
from	O
a	O
combination	O
of	O
the	O
identity	O
of	O
particles	O
,	O
exchange	O
symmetry	O
,	O
and	O
the	O
electrostatic	O
force	O
.	O
</s>
<s>
To	O
illustrate	O
the	O
concept	O
of	O
exchange	B-General_Concept
interaction	I-General_Concept
,	O
any	O
two	O
electrons	O
,	O
for	O
example	O
,	O
in	O
the	O
universe	O
are	O
considered	O
indistinguishable	O
particles	O
,	O
and	O
so	O
according	O
to	O
quantum	O
mechanics	O
in	O
3	O
dimensions	O
,	O
every	O
particle	O
must	O
behave	O
as	O
a	O
boson	O
or	O
a	O
fermion	O
.	O
</s>
<s>
In	O
the	O
former	O
case	O
,	O
two	O
(	O
or	O
more	O
)	O
particles	O
can	O
occupy	O
the	O
same	O
quantum	O
state	O
and	O
this	O
results	O
in	O
an	O
exchange	B-General_Concept
interaction	I-General_Concept
between	O
them	O
in	O
the	O
form	O
of	O
attraction	O
;	O
in	O
the	O
latter	O
case	O
,	O
the	O
particles	O
can	O
not	O
occupy	O
the	O
same	O
state	O
according	O
to	O
the	B-General_Concept
Pauli	I-General_Concept
exclusion	I-General_Concept
principle	I-General_Concept
.	O
</s>
<s>
This	O
repulsion	O
is	O
what	O
the	O
exchange	B-General_Concept
interaction	I-General_Concept
models	O
.	O
</s>
<s>
Where	O
wave	O
functions	O
of	O
electrons	O
overlap	O
,	O
Pauli	B-General_Concept
repulsion	I-General_Concept
takes	O
place	O
.	O
</s>
<s>
The	O
same	O
is	O
true	O
for	O
protons	B-Application
and	O
neutrons	B-Device
where	O
due	O
to	O
their	O
larger	O
mass	O
,	O
the	O
rigidity	O
of	O
baryons	O
is	O
much	O
larger	O
than	O
that	O
of	O
electrons	O
.	O
</s>
