  Intelligent reflecting surfaces (IRSs) have recently attracted the attention
of communication theorists as a means to control the wireless propagation
channel. It has been shown that the signal-to-noise ratio (SNR) of a
single-user IRS-aided transmission increases as $N^2$, with $N$ being the
number of passive reflecting elements in the IRS. This has been interpreted as
a major potential advantage of using IRSs, instead of conventional Massive MIMO
(mMIMO) whose SNR scales only linearly in $N$. This paper shows that this
interpretation is incorrect. We first prove analytically that mMIMO always
provides higher SNRs, and then show numerically that the gap is substantial; a
very large number of reflecting elements is needed for an IRS to obtain SNRs
comparable to mMIMO.
