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Does time exist? The answer to this question may seem obvious: Of course it does! Just look at a calendar or a clock. But developments in physics suggest the non-existence of time is an open possibility, and one that we should take seriously. How can that be, and what would it mean? It'll take a little while to explain, but don't worry: Even if time doesn't exist, our lives will go on as usual. A crisis in physics Physics is in crisis. For the past century or so, we have explained the Universe with two wildly successful physical theories: general...

Last year, scientists detected the most energetic gamma ray burst we've ever seen. A distant galaxy spat out a colossal flare in the range of a trillion electron volts (TeV), providing invaluable new insight into the physics of these incredibly energetic events. That was pretty amazing on its own - but now astrophysicists have used the burst to perform a new, precise test of the theory of general relativity. And - quelle surprise! - this test found that the speed of light is constant in a vacuum. Relativity, once again, has passed with flying colours. The test hinges on a...

As a quantum theory of gravity, loop quantum gravity could potentially solve one of the biggest problems in physics: reconciling general relativity and quantum mechanics. But like all tentative theories of quantum gravity, loop quantum gravity has never been experimentally tested. Now in a new study, scientists have found that, when black holes evaporate, the radiation they emit could potentially reveal “footprints” of loop quantum gravity, distinct from the usual Hawking radiation that black holes are expected to emit. In this way, evaporating black holes could enable the first ever experimental test for any theory of quantum gravity. However, the...

According to string theory, the universe is composed of tiny, vibrating strings rather than point-like particles. Depending on a particular string's mode of vibration, it would take on the characteristics of some particular particle -- an electron, for example, or a photon of light... In its latest incarnation it is known as "M-Theory," in which one-dimensional strings are replaced by higher-dimensional membranes, or "branes" for short. Although some of these branes may be microscopic, others could be large, or perhaps even infinite -- with important implications for cosmology... While string theory begins with matter, loop quantum gravity begins with space...

String theorists state that electrons, photons, protons, and all other particles are not zero-dimensional point-like objects (which form the basis of the Standard Model) but rather tiny one-dimensional extended objects that behave like strings. A group of strings vibrate at a specific resonant frequency -- similar to the movement of strings to produce different sounds on musical instruments such as the violin and guitar -- depending on what type of particle they are, such as electron, photon, proton, and so forth. Over the years, string theorists have not generated any experimental data based on fundamental physical law that proves or...