Noron theory
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The Noron theory suggests a theoretical means in which to 'travel' to the past using the concept of retarded time. It was proposed in 2008 by Professor Richard Hills<ref>Astrophysics Group members - R Hills</ref> of Cambridge University, in honour of the late Jayesh Noron (a close friend of Hills).
Retarded time
The concept of retarded time simply implies that light takes time to travel; that is, light does not travel instantaneously. The retarded time is the time delay from when a light particle (photon) leaves its source, to when it arrives at its destination. Because light travels at extremely high velocities, this delay is typically unnoticeable in small-scale contexts. For example, the time delay from when one turns on a lightbulb to when the photons from that lightbulb reach the observer's eyes is of the order of a billionth of a second. However, on much larger scales (such as between the Sun and the Earth), the time delay is much more noticeable - in the example just mentioned, the retarded time is approximately eight minutes.
One may capitalise on the concept of retarded time to witness events that have happened in the past, simply by traveling far away from the source of the photons. The further one travels away from the source, the further back in time they will be able to see, provided they use extremely large and powerful telescopes. For instance, someone who is the Sun's distance away from the Earth will be able to witness events on the Earth that transpired eight minutes ago.<ref>Charles Seife, Alpha and Omega: The Search for the Beginning and End of the Universe, Penguin 2004.</ref>.
Noron Paradox
There is a problem, however, if the observer wishes to witness events further back in time from their departure from Earth. One may think of the light reflected off Earth as layers of photons emanating from Earth at the speed of light. If one wishes to witness a layer of light from the past, it would require them to travel through space faster than the speed of light to catch up to that layer. Because it is impossible to travel faster than the speed of light (unless you utilise wormhole transportation), the layers of light from the Earth's past are now beyond human reach. This discrepancy is called the Noron Paradox.
Universe curvature
The Noron theory solves the Noron Paradox with modern theories on the curvature of the universe<ref>Probing for dynamics of dark energy and curvature of universe with latest cosmological observations Gong-Bo Zhao (Inst. of High Energy Phys., Chinese Acad. of Sci., Beijing, China); Jun-Qing Xia; Hong Li; Tao, C.; Virey, J.-M.; Zong-Hong Zhu; Xinmin Zhang Source: Physics Letters B, v 648, n 1, 26 April 2007, p 8-13</ref>. The Noron theory suggests that the curvature of the universe is sufficient to eventually refract Earth-originating photons back to Earth. This means that events that have transpired in Earth's past could be witnessed from Earth, using high-powered telescopes. However, the radius of curvature of the universe will determine how far back in time one will be able to 'see.'
The Noron theory has not penetrated mainstream astrophysics and is not well known, as Hills is continuing research on the Noron theory and has not yet published it.
References
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