Abstract
The gravitational field of a laser pulse of finite lifetime, is investigated in the framework of linearized gravity. Although the effects are very small, they may be of fundamental physical interest. It is shown that the gravitational field of a linearly polarized light pulse is modulated as the norm of the corresponding electric field strength, while no modulations arise for circular polarization. In general, the gravitational field is independent of the polarization direction. It is shown that all physical effects are confined to spherical shells expanding with the speed of light, and that these shells are imprints of the spacetime events representing emission and absorption of the pulse. Nearby test particles at rest are attracted towards the pulse trajectory by the gravitational field due to the emission of the pulse, and they are repelled from the pulse trajectory by the gravitational field due to its absorption. Examples are given for the size of the attractive effect. It is recovered that massless test particles do not experience any physical effect if they are co-propagating with the pulse, and that the acceleration of massless test particles counter-propagating with respect to the pulse is four times stronger than for massive particles at rest. The similarities between the gravitational effect of a laser pulse and Newtonian gravity in two dimensions are pointed out. The spacetime curvature close to the pulse is compared to that induced by gravitational waves from astronomical sources.
Highlights
A pulse of light carries energy and momentum, and it is deflected by the gravitational field of a massive body
It is shown that the gravitational field of a linearly polarized light pulse is modulated as the norm of the corresponding electric field strength, while no modulations arise for circular polarization
We argued that the gravitational fields of emitter and absorber can be neglected for the distance ρ to the pulse small in comparison to the distance r to emitter and absorber
Summary
A pulse of light carries energy and momentum, and it is deflected by the gravitational field of a massive body. It is well established that the gravitational field of light is twice that of a material source of the same energy-mass density, that a pulse of light on an infinite straight path is accompanied by a co-propagating plane fronted gravitational wave, and that two such pulses would never interact if propagating on parallel tracks in the same direction ‡. We derive the gravitational field which comes with a laser pulse, using the framework of linearized gravity. The process of emission and absorption of the pulse is included This accounts for the very nature of the electromagnetic field as the mediator of the electromagnetic interaction between material bodies and at the same time avoids the above mentioned calamities which come with massless excitations on unbound trajectories.
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