Misplaced Pages

This is an old revision of this page, as edited by Hublolly (talk | contribs) at 18:59, 9 July 2012 (remove excessive colouration). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Part of a series on
Classical mechanics
${\displaystyle {\textbf {F}}={\frac {d\mathbf {p} }{dt}}}$Second law of motion
History Timeline Textbooks
Branches Applied Celestial Continuum Dynamics Field theory Kinematics Kinetics Statics Statistical mechanics
Fundamentals Acceleration Angular momentum Couple D'Alembert's principle Energy kinetic potential Force Frame of reference Inertial frame of reference Impulse Inertia / Moment of inertia Mass Mechanical power Mechanical work Moment Momentum Space Speed Time Torque Velocity Virtual work
Formulations Newton's laws of motion Analytical mechanics Lagrangian mechanics Hamiltonian mechanics Routhian mechanics Hamilton–Jacobi equation Appell's equation of motion Koopman–von Neumann mechanics
Core topics Damping Displacement Equations of motion Euler's laws of motion Fictitious force Friction Harmonic oscillator Inertial / Non-inertial reference frame Motion (linear) Newton's law of universal gravitation Newton's laws of motion Relative velocity Rigid body dynamics Euler's equations Simple harmonic motion Vibration
Rotation Circular motion Rotating reference frame Centripetal force Centrifugal force reactive Coriolis force Pendulum Tangential speed Rotational frequency Angular acceleration / displacement / frequency / velocity
Scientists Kepler Galileo Huygens Newton Horrocks Halley Maupertuis Daniel Bernoulli Johann Bernoulli Euler d'Alembert Clairaut Lagrange Laplace Poisson Hamilton Jacobi Cauchy Routh Liouville Appell Gibbs Koopman von Neumann
Physics portal  Category
v t e

Hamiltonian mechanics is a reformulation of classical mechanics that was introduced in 1833 by Irish mathematician William Rowan Hamilton.

It arose from Lagrangian mechanics, a previous reformulation of classical mechanics introduced by Joseph Louis Lagrange in 1788, but can be formulated without recourse to Lagrangian mechanics using symplectic spaces (see Mathematical formalism, below). The Hamiltonian method differs from the Lagrangian method in that instead of expressing second-order differential constraints on an n-dimensional coordinate space (where n is the number of degrees of freedom of the system), it expresses first-order constraints on a 2n-dimensional phase space.

As with Lagrangian mechanics, Hamilton's equations provide a new and equivalent way of looking at Newtonian physics. Generally, these equations do not provide a more convenient way of solving a particular problem in classical mechanics. Rather, they provide deeper insights into both the general structure of classical mechanics and its connection to quantum mechanics as understood through Hamiltonian mechanics, as well as its connection to other areas of science.

Simplified overview of uses

The value of the Hamiltonian is the total energy of the system being described. For a closed system, it is the sum of the kinetic and potential energy in the system. There is a set of differential equations known as the Hamilton equations which give the time evolution of the system. Hamiltonians can be used to describe such simple systems as a bouncing ball, a pendulum or an oscillating spring in which energy changes from kinetic to potential and back again over time. Hamiltonians can also be employed to model the energy of other more complex dynamic systems such as planetary orbits in celestial mechanics and also in quantum mechanics.

The Hamilton equations are generally written as follows:

${\displaystyle {\begin{aligned}&{\dot {p}}_{j}=-{\frac {\partial {\mathcal {H}}}{\partial q_{j}}}\\&{\dot {q}}_{j}=+{\frac {\partial {\mathcal {H}}}{\partial p_{j}}}\end{aligned}}}$

where the dot denotes the ordinary derivative with respect to time of the generalized coordinates q_j = q_j(t) and generalized momenta p_j = p_j(t), where j = 1,2...n.

More explicitly, one can equivalently write

${\displaystyle {\frac {\mathrm {d} }{\mathrm {d} t}}\mathbf {p} (t)=-{\frac {\partial }{\partial \mathbf {q} }}{\mathcal {H}}(\mathbf {q} (t),\mathbf {p} (t),t)}$

${\displaystyle {\frac {\mathrm {d} }{\mathrm {d} t}}\mathbf {q} (t)=+{\frac {\partial }{\partial \mathbf {p} }}{\mathcal {H}}(\mathbf {q} (t),\mathbf {p} (t),t)}$

where the functions q and p take values in a vector space, and function ${\displaystyle {\mathcal {H}}={\mathcal {H}}(\mathbf {q} ,\mathbf {p} ,t)}$ is the (scalar valued) Hamiltonian function, and specify the domain of values in which the parameter t (time) varies.

Hamilton's equations are symmetric in the generalized coordinates and momenta, meaning the interchange ${\displaystyle \pm q\rightleftharpoons \mp p}$ and hence ${\displaystyle \pm {\dot {q}}\rightleftharpoons \mp {\dot {p}}}$ leaves the equations unchanged. Naturally, the more degrees of freedom the system has, the more complicated its behavior (predicted by the solutions), since the degrees of freedom correspond to the configuration of the system i.e. (generalized) positions, momenta and the rates at which these change (time derivatives). As such, for more than two massive particles the solutions cannot be found exactly - the many-body problem. It is still possible to obtain qualitative knowledge about the system by approximate analysis of the differential equations.

For a detailed derivation of these equations from Lagrangian mechanics, see below.

Basic physical interpretation

The simplest interpretation of the Hamilton equations is as follows, applying them to a one-dimensional system consisting of one particle of mass m under time-independent boundary conditions: The Hamiltonian ${\displaystyle {\mathcal {H}}}$ represents the energy of the system (provided that there are NO external forces, or additional energy added to the system), which is the sum of kinetic and potential energy, traditionally denoted T and V, respectively. Here q is the coordinate and p is the momentum, mv. Then

${\displaystyle {\mathcal {H}}=T+V,\quad T={\frac {p^{2}}{2m}},\quad V=V(q).}$

Note that T is a function of p alone, while V is a function of q alone.

Now the time-derivative of the momentum p equals the Newtonian force, and so here the first Hamilton equation means that the force on the particle equals the rate at which it loses potential energy with respect to changes in its location. (Force equals the negative gradient of potential energy.)

The time-derivative of q means the velocity: the second Hamilton equation here means that the particle’s velocity equals the derivative of its kinetic energy with respect to its momentum. (Because the derivative with respect to p of p/2m equals p/m = mv/m = v.)

Technique of using Hamilton's equations

Hamilton's equations are used in the following way. In terms of the generalized coordinates q_i and generalized velocities q̇_i:

1. The Lagrangian is found, ${\displaystyle {\mathcal {L}}=T-V}$.
2. The momenta are calculated by differentiating the Lagrangian with respect to the (generalized) velocities: ${\displaystyle p_{i}(q_{i},{\dot {q}}_{i},t)={\frac {\partial {\mathcal {L}}}{\partial {{\dot {q}}_{i}}}}}$.
3. The velocities q̇_i are expressed in terms of the momenta p_i by inverting the expressions in the previous step.
4. The Hamiltonian is calculated using the usual definition of H as the Legendre transformation of L: ${\displaystyle {\mathcal {H}}=\sum _{i}{{\dot {q}}_{i}}{\frac {\partial {\mathcal {L}}}{\partial {{\dot {q}}_{i}}}}-{\mathcal {L}}=\sum _{i}{{\dot {q}}_{i}}p_{i}-{\mathcal {L}}}$. Then the velocities are substituted for using the previous results.
5. Hamilton's equations are applied, to obtain the equations of motion of the system.

Deriving Hamilton's equations

Hamilton's equations can be derived by looking at how the total differential of the Lagrangian depends on time, generalized positions ${\displaystyle q_{i}\,}$ and generalized velocities ${\displaystyle {\dot {q}}_{i}:}$

${\displaystyle \mathrm {d} {\mathcal {L}}=\sum _{i}\left({\frac {\partial {\mathcal {L}}}{\partial q_{i}}}\mathrm {d} q_{i}+{\frac {\partial {\mathcal {L}}}{\partial {{\dot {q}}_{i}}}}\mathrm {d} {{\dot {q}}_{i}}\right)+{\frac {\partial {\mathcal {L}}}{\partial t}}\mathrm {d} t\,.}$

Now the generalized momenta were defined as ${\displaystyle p_{i}={\frac {\partial {\mathcal {L}}}{\partial {{\dot {q}}_{i}}}}}$ and Lagrange's equations tell us that

${\displaystyle {\frac {\mathrm {d} }{\mathrm {d} t}}{\frac {\partial {\mathcal {L}}}{\partial {{\dot {q}}_{i}}}}-{\frac {\partial {\mathcal {L}}}{\partial q_{i}}}=0.\,}$

We can rearrange this to get

${\displaystyle {\frac {\partial {\mathcal {L}}}{\partial q_{i}}}={\dot {p}}_{i}\,}$

and substitute the result into the total differential of the Lagrangian

${\displaystyle \mathrm {d} {\mathcal {L}}=\sum _{i}\left+{\frac {\partial {\mathcal {L}}}{\partial t}}\mathrm {d} t\,.}$

We can rewrite this as

${\displaystyle \mathrm {d} {\mathcal {L}}=\sum _{i}\left+{\frac {\partial {\mathcal {L}}}{\partial t}}\mathrm {d} t\,}$

and rearrange again to get

${\displaystyle \mathrm {d} \left(\sum _{i}p_{i}{{\dot {q}}_{i}}-{\mathcal {L}}\right)=\sum _{i}\left-{\frac {\partial {\mathcal {L}}}{\partial t}}\mathrm {d} t\,.}$

The term on the left-hand side is just the Hamiltonian that we have defined before, so we find that

${\displaystyle \mathrm {d} {\mathcal {H}}=\sum _{i}\left-{\frac {\partial {\mathcal {L}}}{\partial t}}\mathrm {d} t=\sum _{i}\left+{\frac {\partial {\mathcal {H}}}{\partial t}}\mathrm {d} t\,}$

where the second equality holds because of the definition of the total differential of ${\displaystyle {\mathcal {H}}}$ in terms of its partial derivatives. Associating terms from both sides of the equation above yields Hamilton's equations

${\displaystyle {\frac {\partial {\mathcal {H}}}{\partial q_{j}}}=-{\dot {p}}_{j}\,,\quad {\frac {\partial {\mathcal {H}}}{\partial p_{j}}}={\dot {q}}_{j}\,,\quad {\frac {\partial {\mathcal {H}}}{\partial t}}=-{\partial {\mathcal {L}} \over \partial t}\,.}$

As a reformulation of Lagrangian mechanics

Starting with Lagrangian mechanics, the equations of motion are based on generalized coordinates

${\displaystyle \left\{\,q_{j}|j=1,\ldots ,N\,\right\}}$

and matching generalized velocities

${\displaystyle \left\{\,{\dot {q}}_{j}|j=1,\ldots ,N\,\right\}.}$

We write the Lagrangian as

${\displaystyle {\mathcal {L}}(q_{j},{\dot {q}}_{j},t)}$

with the subscripted variables understood to represent all N variables of that type. Hamiltonian mechanics aims to replace the generalized velocity variables with generalized momentum variables, also known as conjugate momenta. By doing so, it is possible to handle certain systems, such as aspects of quantum mechanics, that would otherwise be even more complicated.

For each generalized velocity, there is one corresponding conjugate momentum, defined as:

${\displaystyle p_{j}={\partial {\mathcal {L}} \over \partial {\dot {q}}_{j}}.}$

In Cartesian coordinates, the generalized momenta are precisely the physical linear momenta. In circular polar coordinates, the generalized momentum corresponding to the angular velocity is the physical angular momentum. For an arbitrary choice of generalized coordinates, it may not be possible to obtain an intuitive interpretation of the conjugate momenta.

One thing which is not too obvious in this coordinate dependent formulation is that different generalized coordinates are really nothing more than different coordinate patches on the same symplectic manifold (see Mathematical formalism, below).

The Hamiltonian is the Legendre transform of the Lagrangian:

${\displaystyle {\mathcal {H}}\left(q_{j},p_{j},t\right)=\sum _{i}{\dot {q}}_{i}p_{i}-{\mathcal {L}}(q_{j},{\dot {q}}_{j},t).}$

If the transformation equations defining the generalized coordinates are independent of t, and the Lagrangian is a sum of products of functions (in the generalized coordinates) which are homogeneous of order 0, 1 or 2, then it can be shown that H is equal to the total energy E = T + V.

Each side in the definition of ${\displaystyle {\mathcal {H}}}$ produces a differential:

${\displaystyle {\begin{aligned}\mathrm {d} {\mathcal {H}}&=\sum _{i}\left+\left({\partial {\mathcal {H}} \over \partial t}\right)\mathrm {d} t\qquad \qquad \quad \quad \\\\&=\sum _{i}\left-\left({\partial {\mathcal {L}} \over \partial t}\right)\mathrm {d} t.\end{aligned}}}$

Substituting the previous definition of the conjugate momenta into this equation and matching coefficients, we obtain the equations of motion of Hamiltonian mechanics, known as the canonical equations of Hamilton:

${\displaystyle {\frac {\partial {\mathcal {H}}}{\partial q_{j}}}=-{\dot {p}}_{j},\qquad {\frac {\partial {\mathcal {H}}}{\partial p_{j}}}={\dot {q}}_{j},\qquad {\frac {\partial {\mathcal {H}}}{\partial t}}=-{\partial {\mathcal {L}} \over \partial t}.}$

Hamilton's equations are first-order differential equations, and thus easier to solve than Lagrange's equations, which are second-order. Hamilton's equations have another advantage over Lagrange's equations: if a system has a symmetry, such that a coordinate does not occur in the Hamiltonian, the corresponding momentum is conserved, and that coordinate can be ignored in the other equations of the set. Effectively, this reduces the problem from n coordinates to (n-1) coordinates. In the Lagrangian framework, of course the result that the corresponding momentum is conserved still follows immediately, but all the generalized velocities still occur in the Lagrangian - we still have to solve a system of equations in n coordinates.

The Lagrangian and Hamiltonian approaches provide the groundwork for deeper results in the theory of classical mechanics, and for formulations of quantum mechanics.

Geometry of Hamiltonian systems

A Hamiltonian system may be understood as a fiber bundle E over time R, with the fibers E_t, t ∈ R, being the position space. The Lagrangian is thus a function on the jet bundle J over E; taking the fiberwise Legendre transform of the Lagrangian produces a function on the dual bundle over time whose fiber at t is the cotangent space TE_t, which comes equipped with a natural symplectic form, and this latter function is the Hamiltonian.

Generalization to quantum mechanics through Poisson bracket

Hamilton's equations above work well for classical mechanics, but not for quantum mechanics, since the differential equations discussed assume that one can specify the exact position and momentum of the particle simultaneously at any point in time. However, the equations can be further generalized to then be extended to apply to quantum mechanics as well as to classical mechanics, through the deformation of the Poisson algebra over p and q to the algebra of Moyal brackets.

Specifically, the more general form of the Hamilton's equation reads

${\displaystyle {\frac {\mathrm {d} f}{\mathrm {d} t}}=\{f,{\mathcal {H}}\}+{\frac {\partial f}{\partial t}}}$

where f is some function of p and q, and H is the Hamiltonian. To find out the rules for evaluating a Poisson bracket without resorting to differential equations, see Lie algebra; a Poisson bracket is the name for the Lie bracket in a Poisson algebra. These Poisson brackets can then be extended to Moyal brackets comporting to an inequivalent Lie algebra, as proven by H Groenewold, and thereby describe quantum mechanical diffusion in phase space (See the phase space formulation and Weyl quantization). This more algebraic approach not only permits ultimately extending probability distributions in phase space to Wigner quasi-probability distributions, but, at the mere Poisson bracket classical setting, also provides more power in helping analyze the relevant conserved quantities in a system.

Mathematical formalism

Any smooth real-valued function H on a symplectic manifold can be used to define a Hamiltonian system. The function H is known as the Hamiltonian or the energy function. The symplectic manifold is then called the phase space. The Hamiltonian induces a special vector field on the symplectic manifold, known as the Hamiltonian vector field.

The Hamiltonian vector field (a special type of symplectic vector field) induces a Hamiltonian flow on the manifold. This is a one-parameter family of transformations of the manifold (the parameter of the curves is commonly called the time); in other words an isotopy of symplectomorphisms, starting with the identity. By Liouville's theorem, each symplectomorphism preserves the volume form on the phase space. The collection of symplectomorphisms induced by the Hamiltonian flow is commonly called the Hamiltonian mechanics of the Hamiltonian system.

The symplectic structure induces a Poisson bracket. The Poisson bracket gives the space of functions on the manifold the structure of a Lie algebra.

Given a function f

${\displaystyle {\frac {\mathrm {d} }{\mathrm {d} t}}f={\frac {\partial }{\partial t}}f+\{\,f,{\mathcal {H}}\,\}.}$

If we have a probability distribution, ρ, then (since the phase space velocity (${\displaystyle {{\dot {p}}_{i}},{{\dot {q}}_{i}}}$) has zero divergence, and probability is conserved) its convective derivative can be shown to be zero and so

${\displaystyle {\frac {\partial }{\partial t}}\rho =-\{\,\rho ,{\mathcal {H}}\,\}.}$

This is called Liouville's theorem. Every smooth function G over the symplectic manifold generates a one-parameter family of symplectomorphisms and if { G, H } = 0, then G is conserved and the symplectomorphisms are symmetry transformations.

A Hamiltonian may have multiple conserved quantities G_i. If the symplectic manifold has dimension 2n and there are n functionally independent conserved quantities G_i which are in involution (i.e., { G_i, G_j } = 0), then the Hamiltonian is Liouville integrable. The Liouville–Arnol'd theorem says that locally, any Liouville integrable Hamiltonian can be transformed via a symplectomorphism in a new Hamiltonian with the conserved quantities G_i as coordinates; the new coordinates are called action-angle coordinates. The transformed Hamiltonian depends only on the G_i, and hence the equations of motion have the simple form

${\displaystyle {\dot {G}}_{i}=0,\qquad {\dot {\varphi }}_{i}=F(G),}$

for some function F (Arnol'd et al., 1988). There is an entire field focusing on small deviations from integrable systems governed by the KAM theorem.

The integrability of Hamiltonian vector fields is an open question. In general, Hamiltonian systems are chaotic; concepts of measure, completeness, integrability and stability are poorly defined. At this time, the study of dynamical systems is primarily qualitative, and not a quantitative science.

Riemannian manifolds

An important special case consists of those Hamiltonians that are quadratic forms, that is, Hamiltonians that can be written as

${\displaystyle {\mathcal {H}}(q,p)={\frac {1}{2}}\langle p,p\rangle _{q}}$

where ${\displaystyle \langle \cdot ,\cdot \rangle _{q}}$ is a smoothly varying inner product on the fibers ${\displaystyle T_{q}^{*}Q}$, the cotangent space to the point q in the configuration space, sometimes called a cometric. This Hamiltonian consists entirely of the kinetic term.

If one considers a Riemannian manifold or a pseudo-Riemannian manifold, the Riemannian metric induces a linear isomorphism between the tangent and cotangent bundles. (See Musical isomorphism). Using this isomorphism, one can define a cometric. (In coordinates, the matrix defining the cometric is the inverse of the matrix defining the metric.) The solutions to the Hamilton–Jacobi equations for this Hamiltonian are then the same as the geodesics on the manifold. In particular, the Hamiltonian flow in this case is the same thing as the geodesic flow. The existence of such solutions, and the completeness of the set of solutions, are discussed in detail in the article on geodesics. See also Geodesics as Hamiltonian flows.

Sub-Riemannian manifolds

When the cometric is degenerate, then it is not invertible. In this case, one does not have a Riemannian manifold, as one does not have a metric. However, the Hamiltonian still exists. In the case where the cometric is degenerate at every point q of the configuration space manifold Q, so that the rank of the cometric is less than the dimension of the manifold Q, one has a sub-Riemannian manifold.

The Hamiltonian in this case is known as a sub-Riemannian Hamiltonian. Every such Hamiltonian uniquely determines the cometric, and vice-versa. This implies that every sub-Riemannian manifold is uniquely determined by its sub-Riemannian Hamiltonian, and that the converse is true: every sub-Riemannian manifold has a unique sub-Riemannian Hamiltonian. The existence of sub-Riemannian geodesics is given by the Chow-Rashevskii theorem.

The continuous, real-valued Heisenberg group provides a simple example of a sub-Riemannian manifold. For the Heisenberg group, the Hamiltonian is given by

${\displaystyle {\mathcal {H}}(x,y,z,p_{x},p_{y},p_{z})={\frac {1}{2}}\left(p_{x}^{2}+p_{y}^{2}\right).}$

${\displaystyle p_{z}}$ is not involved in the Hamiltonian.

Poisson algebras

Hamiltonian systems can be generalized in various ways. Instead of simply looking at the algebra of smooth functions over a symplectic manifold, Hamiltonian mechanics can be formulated on general commutative unital real Poisson algebras. A state is a continuous linear functional on the Poisson algebra (equipped with some suitable topology) such that for any element A of the algebra, A² maps to a nonnegative real number.

A further generalization is given by Nambu dynamics.

Charged particle in an electromagnetic field

A good illustration of Hamiltonian mechanics is given by the Hamiltonian of a charged particle in an electromagnetic field. In Cartesian coordinates (i.e. ${\displaystyle q_{i}=x_{i}}$), the Lagrangian of a non-relativistic classical particle in an electromagnetic field is (in SI Units):

${\displaystyle {\mathcal {L}}=\sum _{i}{\tfrac {1}{2}}m{\dot {x}}_{i}^{2}+\sum _{i}e{\dot {x}}_{i}A_{i}-e\phi ,}$

where e is the electric charge of the particle (not necessarily the electron charge), ${\displaystyle \phi }$ is the electric scalar potential, and the ${\displaystyle A_{i}}$ are the components of the magnetic vector potential (these may be modified through a gauge transformation). This is called minimal coupling.

The generalized momenta may be derived by:

${\displaystyle p_{j}={\frac {\partial L}{\partial {\dot {x}}_{j}}}=m{\dot {x}}_{j}+eA_{j}.}$

Rearranging, we may express the velocities in terms of the momenta, as:

${\displaystyle {\dot {x}}_{j}={\frac {p_{j}-eA_{j}}{m}}.}$

If we substitute the definition of the momenta, and the definitions of the velocities in terms of the momenta, into the definition of the Hamiltonian given above, and then simplify and rearrange, we get:

${\displaystyle {\mathcal {H}}=\sum _{i}{\dot {x}}_{i}p_{i}-{\mathcal {L}}=\sum _{i}{\frac {(p_{i}-eA_{i})^{2}}{2m}}+e\phi .}$

This equation is used frequently in quantum mechanics.

Relativistic charged particle in an electromagnetic field

The Lagrangian for a relativistic charged particle is given by:

${\displaystyle {\mathcal {L}}=-mc^{2}{\sqrt {1-{\frac {{{\dot {\vec {x}}}}^{2}}{c^{2}}}}}-e\phi ,t]+e{\dot {\vec {x}}}\cdot {\vec {A}},t]\,.}$

Thus the particle's canonical (total) momentum is

${\displaystyle {\vec {P}}\,={\frac {\partial {\mathcal {L}}}{\partial {\dot {\vec {x}}}}}={\frac {m{\dot {\vec {x}}}}{\sqrt {1-{\frac {{{\dot {\vec {x}}}}^{2}}{c^{2}}}}}}+e{\vec {A}},t]\,,}$

that is, the sum of the kinetic momentum and the potential momentum.

Solving for the velocity, we get

${\displaystyle {\dot {\vec {x}}}={\frac {{\vec {P}}\,-e{\vec {A}},t]}{\sqrt {m^{2}+{\frac {1}{c^{2}}}{\left({\vec {P}}\,-e{\vec {A}},t]\right)}^{2}}}}\,.}$

So the Hamiltonian is

${\displaystyle {\mathcal {H}}={\dot {\vec {x}}}\cdot {\vec {P}}\,-{\mathcal {L}}=c{\sqrt {m^{2}c^{2}+{\left({\vec {P}}\,-e{\vec {A}},t]\right)}^{2}}}+e\phi ,t]\,.}$

From this we get the force equation (equivalent to the Euler–Lagrange equation)

${\displaystyle {\dot {\vec {P}}}=-{\frac {\partial {\mathcal {H}}}{\partial {\vec {x}}}}=e({\vec {\nabla }}{\vec {A}})\cdot {\dot {\vec {x}}}-e{\vec {\nabla }}\phi \,}$

from which one can derive

${\displaystyle {\frac {d}{dt}}\left({\frac {m{\dot {\vec {x}}}}{\sqrt {1-{\frac {{\dot {\vec {x}}}^{2}}{c^{2}}}}}}\right)=e{\vec {E}}+e{\dot {\vec {x}}}\times {\vec {B}}\,.}$

An equivalent expression for the Hamiltonian as function of the relativistic (kinetic) momentum, ${\displaystyle {\vec {p}}=\gamma m{\dot {\vec {x}}}\,,}$ is

${\displaystyle {\mathcal {H}}={\dot {\vec {x}}}\cdot {\vec {p}}\,+{\frac {mc^{2}}{\gamma }}+e\phi ,t]=\gamma mc^{2}+e\phi ,t]=E+V\,.}$

This has the advantage that ${\displaystyle {\vec {p}}}$ can be measured experimentally whereas ${\displaystyle {\vec {P}}}$ cannot. Notice that the Hamiltonian (total energy) can be viewed as the sum of the relativistic energy (kinetic+rest), ${\displaystyle E=\gamma mc^{2}\,,}$ plus the potential energy, ${\displaystyle V=e\phi \,.}$

See also

• Canonical transformation
• Classical field theory
• Classical mechanics
• Dynamical systems theory
• Hamilton–Jacobi equation
• Lagrangian mechanics
• Maxwell's equations
• Hamiltonian (quantum mechanics)
• Quantum Hamilton's equations
• Quantum field theory
• Hamiltonian optics

References

Footnotes

1. LaValle, Steven M. (2006), "§13.4.4 Hamiltonian mechanics", Planning Algorithms, Cambridge University Press, ISBN 978-0-521-86205-9
2. "16.3 The Hamiltonian", MIT OpenCourseWare website 18.013A, retrieved February 2007 {{citation}}: Check date values in: |accessdate= (help)
3. Analytical Mechanics, L.N. Hand, J.D. Finch, Cambridge University Press, 2008, ISBN 978-0-521-57572-0
4. The Road to Reality, Roger Penrose, Vintage books, 2007, ISBN 0-679-77631-1
5. This derivation is along the lines as given in Arnol'd 1989, pp. 65–66
6. Goldstein, H. (2001), Classical Mechanics (3rd ed.), Addison-Wesley, ISBN 0-201-65702-3

Other

• Arnol'd, V. I. (1989), Mathematical Methods of Classical Mechanics, Springer-Verlag, ISBN 0-387-96890-3
• Abraham, R.; Marsden, J.E. (1978), Foundations of Mechanics, London: Benjamin-Cummings, ISBN 0-8053-0102-X
• Arnol'd, V. I.; Kozlov, V. V.; Neĩshtadt, A. I. (1988), Mathematical aspects of classical and celestial mechanics, vol. 3, Springer-Verlag {{citation}}: Unknown parameter |booktitle= ignored (help)
• Vinogradov, A. M.; Kupershmidt, B. A. (1981), The structure of Hamiltonian mechanics (DjVu), London Math. Soc. Lect. Notes Ser., vol. 60, London: Cambridge Univ. Press

External links

• Binney, James J., Classical Mechanics (lecture notes) (PDF), University of Oxford, retrieved 27 October 2010
• Tong, David, Classical Dynamics (Cambridge lecture notes), University of Cambridge, retrieved 27 October 2010

• Hamilton, William Rowan, On a General Method in Dynamics, Trinity College Dublin

Template:Physics equations navbox

• Fundamental physics concepts
• Classical mechanics
• Hamiltonian mechanics
• Dynamical systems
• Symplectic geometry