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I am not a String Theorist, but I just want to ask if there is anything which specifies a quantum of time, as per M-theory?

Can a quantity such as $$ t_p = \left(\frac{\ell_p}{c}\right),$$

where $\ell_p$ is Planck length and $c$ speed of light in vacuum, be called as time quantum?

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would this just be planck time? – Nic Nov 4 '11 at 13:56
so der does exist such a thing as planck time!!!...okay i got a wiki – Vineet Menon Nov 4 '11 at 16:29

There are no quanta of time in string / M-theory. It is rather LQG and similar approaches that evolve in discrete time steps. But this is a bad thing for the uncertainty principle of quantum mechanics, as is clearly shown by a quite easily accessible calculation here

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As others have said, what you've calculated is the Plank time. Remember though that the Plank units are defined such that many important constants have the numerical value $1$. Many theories start to "break down" and provide nonsensical answers about distances as short as the Plank length or energies as high as the Plank energy or events as short as the Plank time.

It may be that space and time are quantized near the Plank length and time but no theory we have specifically points to that. Instead they point to a breakdown in the theory for which quantization is but one hypothesis for what might happen.

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That is Planck time. See for more information.

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