Space–time wave packets that travel in optical materials at the speed of light in vacuum
Can associate optical pulse traverse a non-dispersive material at the speed of sunshine in vacuum? as a result of ancient approaches for dominant the cluster speed of light manipulate either the fabric or structural resonances, associate absence of dispersion altogether seems to exclude such a possibility. Here we have a tendency to demonstrate in theory and through an experiment that “space–time” wave packets—pulsed beams during which the spacial and temporal degrees of freedom are tightly intertwined—can so traverse a non-dispersive clear optical material at the speed of sunshine in vacuum. we have a tendency to synthesize wave packets whose spatio-temporal spectra lie on the intersection of the material’s light-cone with a spectral hyperplane canted to coincide with the vacuum light-line. By measure the cluster delay interferometrically with regard to a generic reference pulse, we have a tendency to ensure that the wave packet cluster speed in a very kind of materials (including water, glass, and sapphire) is that the speed of sunshine in vacuum. 
Evidences for Varying Speed of Light with Time
Aims: The paper explores the hypothesis that the speed of sunshine c is decreasing over time at rate (dc/dt)=-H⋅ c, H being the Hubble constant. This hypothesis differs from the questionable tired lightweight, within which the speed c is meant to vary throughout the journey of photons within the empty area for a few resistance mechanism. within the hypothesis of the author the speed c, throughout this journey, is assumed constant. during this approach the issues of the tired hypothesis are overcome. Methods: The paper links the variation dc/dt with the Hubble constant and infers a price of dc/dt from the distinction between the worth of the variation of the Earth-Moon distance measured by the satellite optical maser travel Experiment and also the recurrent event impact. Results: below the hypothesis c time variable, we have a tendency to explain: 1) The cosmological redshift. 2) The abnormal acceleration ap ≈ -8 × 10-10 m⋅sec-2, measured for a few spacecrafts. 3) The high redshift of supernovae American state, that appears to proof AN acceleration of the enlargement of the universe. 4) The peripheral motion of stars in galaxies around their motion centre. 5) The dilation of the sunshine curves determined for supernovae American state. 
Dispersive property of the quantum vacuum and the speed of light
We want to check the influence of the quantum vacuum on light-weight propagation. At first, by operating within the normal linear scientific theory of the magnetism fields, it’s shown that the electrical permittivity and also the magnetic porosity of the vacuum medium are changed; however, the ensuing speed of sunshine isn’t changed. Then, taking under consideration nonlinear effects by considering the Euler–Heisenberg Lagrangian, the corresponding numerical quantity (vacuum) energy and also the ensuing modification of the speed of sunshine are found up to the primary nonvanishing correction. 
Simple Animations by a NASA Scientist ‘Prove’ The Speed of Light Is Torturously Slow
A series of recent animations by a NASA mortal show simply however zippy – and additionally how agonizingly slow – the speed of sunshine may be.
Light speed is that the quickest that any material object will travel through house. That is, of course, exclusion the existence of theoretical shortcuts within the cloth of house known as wormholes (and the flexibility to travel through them while not being destroyed).
In a utterly empty vacuum, a particle of sunshine, that is termed a gauge boson, will travel 186,282 miles per second (299,792 kilometers per second), or regarding 670.6 million mph (1.079 billion kilometers per hour).
This is implausibly quick. However, c may be frustratingly slow if you’re making an attempt to speak with or reach alternative planets, particularly any worlds on the far side our scheme.
To depict the ordinance of the cosmos in an exceedingly means anyone may perceive, James O’Donoghue, a planetary mortal at NASA’s physicist house Flight Center, took it upon himself to animate it.
“My animations were created to indicate as instantly as attainable the full context of what I’m making an attempt to convey,” O’Donoghue told Business business executive via Twitter. “When I revised for my exams, I wont to draw complicated ideas out by hand simply to actually perceive, thus that’s what I’m doing here.”
O’Donoghue same he solely recently learned the way to produce these animations – his 1st were for a NASA news unharness regarding Saturn’s vanishing rings. After that, he affected on to enlivening alternative difficult-to-grasp house ideas, together with a video illustrating the rotation speeds and sizes of the planets. He same that one “garnered immeasurable views” once he denote it on Twitter.
O’Donoghue’s latest effort appearance at 3 totally different light-speed situations to convey how briskly (and however painfully slow) photons may be. 
Two-way and One-way Vacuum Speed of Light under the Membrane Paradigm
The discovery of cosmic microwave background (CMB) by Wilson and Penzias defines a rest frame the sense of Newton’s space. This reality is one in all the explanations why brane worlds stirred into the main target of interest. Membrane theory (CM) uses the cosmological model of a four-dimensional skinny membrane, increasing in hyperspace. A homogenised vector field acts sheer from outside onto the membrane and causes, this way, curvature of area and gravitation. The membrane defines AN absolute Newtonian area, and forces tiny changes of theory of relativity (SR). the foremost vital distinction between CM and SR is that the introduction of a cross contraction of moving bodies.
Photons travel forever and solely within the rest mechanical phenomenon reference system. there’s no distinction between two-way and unidirectional speed of sunshine. far-flung from plenty photons move with constant speed c. the remainder mechanical phenomenon reference system is outlined by the absence of the dipole of the cosmic microwave background (CMB), caused by the Doppler-effect. The speed of sunshine is eolotropic in every mechanical phenomenon reference system that’s in relative motion with regard to the remainder frame. though the speed of sunshine is constant within the vacuum, it are often measured on Earth solely with a scientific error of ± thirty six.9 m/s. the explanation is that the flow of your time of the clocks on the planet isn’t constant.
The mensuration of the unidirectional speed of sunshine could be a special issue. though the speed of sunshine is eolotropic in every moving mechanical phenomenon reference system, the time transformation hides this reality nearly absolutely. A co-moving observer registers the arrival of the sunshine signal once a interval that suggests that speed of sunshine is usually c. to get this result, it’s spare to just accept the existence of a rest mechanical phenomenon reference system and also the transformation of your time given by FitzGerald and Lorentz. 
 Bhaduri, B., Yessenov, M. and Abouraddy, A.F., 2019. Space–time wave packets that travel in optical materials at the speed of light in vacuum. Optica, 6(2), pp.139-146. (Web Link)
 Pipino, G., 2019. Evidences for Varying Speed of Light with Time. Journal of High Energy Physics, Gravitation and Cosmology, 5(2). (Web Link)
 Razmi, H., Baramzadeh, N. and Baramzadeh, H., 2019. Dispersive property of the quantum vacuum and the speed of light. Modern Physics Letters A, p.1950035. (Web Link)
 Simple Animations by a NASA Scientist ‘Prove’ The Speed of Light Is Torturously Slow
DAVE MOSHER, BUSINESS INSIDER
19 JAN 2019 (Web Link)
 Two-way and One-way Vacuum Speed of Light under the Membrane Paradigm
Stefan von Weber
Faculty Medical and Life Sciences, Furtwangen University, Jakob-Kienzle-Strasse 14, 78054 Villingen-Schwenningen, Germany
Alexander von Eye
Department of Psychology, Michigan State University, Psychology Building, 318 Physics Rm 262, East Lansing, MI 48824, USA (Web Link)