OrphanWilde comments on Open Thread, April 15-30, 2013 - Less Wrong

4 Post author: diegocaleiro 15 April 2013 07:57PM

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Comment author: OrphanWilde 18 April 2013 05:14:40PM *  1 point [-]

Er, 1/0 * 0 != 1.

The law of cancellation requires that all values being cancelled have an inverse. The inverse of 0 doesn't exist in the set of real numbers (although it does exist in the hyperreals). This doesn't mean you can't multiply a number by the inverse of 0, but the product doesn't exist in real numbers, either. (Hyperreal numbers don't cancel out the way real numbers do, however; they can leave behind a hyperreal component [ETA: Or at least that's my understanding from the way my instructor explained why removable discontinuities couldn't actually be removed - open to proof otherwise].)

Comment author: Khoth 18 April 2013 05:50:15PM 10 points [-]

0 doesn't have an inverse in the hyperreal numbers either (To see why this it true, consider the first-order statement "∀x, x*0 != 1" which is true in the real numbers and therefore also true in the hyperreals by the transfer principle). From this it obviously follows that you can't multiply a number by the inverse of 0.

Comment author: [deleted] 18 April 2013 06:14:18PM 2 points [-]

Further, if you did decide to adjoin an inverse of zero to the hyperreals, the result would be the zero ring.

Comment author: OrphanWilde 18 April 2013 06:31:00PM 1 point [-]

Going to have to investigate more, but that looks solid.