“Some of the effects predicted by the theory [of loop quantum gravity] appear to be in conflict with one of the principles of Einstein's special theory of relativity… that the speed of light is a universal constant. …Photons of higher energy travel slightly slower than low-energy photons. …the principle of [general] relativity is preserved but Einstein's special theory of relativity requires modification. …A photon can have an energy-dependent speed without violating the principle of [general] relativity!”

— Lee Smolin

"Loop Quantum Gravity," The New Humanists: Science at the Edge (2003)

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Lee Smolin 52

American cosmologist 1955

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“The miracle of physics that I'm talking about here is something that was actually known since the time of Einstein's general relativity; that gravity is not always attractive. Gravity can act repulsively. Einstein introduced this in 1916… in the form of the cosmological constant, and the original motivation of modifying the equations of general relativity to allow this was because Einstein thought that the universe was static, and he realized that ordinary gravity would cause the universe to collapse if it was static. …The fact that general relativity can support this gravitational repulsion, still being consistent with all the principles that general relativity incorporates, is the important thing which Einstein himself did discover..”

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“Einstein's theory of relativity”

Hermann Weyl (1885–1955) German mathematician

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“The last thirty years of Einstein's life were largely devoted to a search for a so-called unified field theory that would unify James Clerk Maxwell's theory of electromagnetism with the general theory of relativity, Einstein's theory of gravitation. Einstein's attempt was not successful, and with hindsight we can now see that it was misconceived. Not only did Einstein reject quantum mechanics; the scope of his effort was too narrow. … Nevertheless Einstein's struggle is our struggle today. It is the search for a final theory.”

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“E = mc2 really applies only to isolated bodies at rest. In general, when you have moving bodies, or interacting bodies, energy and mass aren't proportional. E = mc2 simply doesn't apply. …For moving bodies, the correct mass-energy equation is
E=\frac {mc^2} {\sqrt{1-\frac{v^2} {c^2}}}
where v is the velocity. For a body at rest (v=0), this becomes E = mc2. …we must consider the special case of particles with zero mass… examples include photons, color gluons, and gravitons. If we attempt to put m = 0 and v = c in our general mass-energy equation, both the numerator and denominator on the right-hand-side vanish, and we get the nonsensical relation E = 0/0. The correct result is that the energy of a photon can take any value. …The energy E of a photon is proportional to the frequency f of the light it represents. …they are related by the Planck-Einstein-Schrödinger equation E = hf, where h is Plank's constant.”

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when the velocity <math>v</math> approaches the speed of light c, the denominator approaches 0 thus E approaches infinity, unless m = 0.
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“Jesus could not have imagined such an idea as Albert Einstein's theory of relativity.”

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E. C. George Sudarshan (1931–2018) Indian physicist

in A Glance Back at Five Decades of Scientific Research, published in Particles and Fields: Classical and Quantum, Journal of Physics: Conference Series 87 (2007), IOP Publishing, p. 1-2.

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