By firing a pulse of light at a semi-transparent/semi-reflective thin medium, researchers can measure the time it must take for these photons to tunnel through the barrier to the other side. Although the step of tunneling itself may be instantaneous, the traveling particles are still limited by the speed of light. By taking high-speed images of this light pulse, we can construct a movie that appears continuous.
Credit: J. Liang, L. Zhu & L.V. Wang, 2018, Light: Science & Applications
You can live forever ... if you're a photon. :)
In the expanding Universe, for billions upon billions of years, the photon seems to be one of the very few particles that has an apparently infinite lifetime. Photons are the quanta that compose light, and in the absence of any other interactions that force them to change their properties, are eternally stable, with no hint that they would transmute into any other particle. But how well do we know this to be true, and what evidence can we point to in order to determine their stability? It's a fascinating question that pushes us right to the limits of what we can scientifically observe and measure.
One of the most enduring ideas in all the Universe is that everything that exists now will someday see its existence come to an end. The stars, galaxies, and even the black holes that occupy the space in our Universe will all some day burn out, fade away, and otherwise decay, leaving what we think of as a “heat death” state: where no more energy can possibly be extracted, in any way, from a uniform, maximum entropy, equilibrium state. But, perhaps, there are exceptions to this general rule, and that some things will truly live on forever.
Light may be emitted at a particular wavelength, but the expansion of the Universe will stretch it as it travels. Light emitted in the ultraviolet will be shifted all the way into the infrared when considering a galaxy whose light arrives from 13+ billion years ago. The more the expansion of the Universe accelerates, the greater the light from distant objects will be redshifted and the fainter it will appear.
It gets better.
Through the vacuum of space, all light, regardless of wavelength or energy, travels at the same speed: the speed of light in a vacuum. When we observe light from a distant star, we are observing light that has already completed that journey from the source to the observer.
The big fundamental ...
Even at its very end, no matter how far into the future we go, the Universe will always continue to produce radiation, ensuring that it will never reach absolute zero, that it will always contain photons, and that even at the lowest energies it will ever reach, there ought to be nothing else for the photon to decay or transition into. Although the energy density of the Universe will continue to drop as the Universe expands, and the energy inherent to any individual photon will continue to drop as time ticks onward and onward into the future, there will never be anything “more fundamental” that they transition into.
And so it begins ...
No comments:
Post a Comment