ARGUMENTS IN SUPPORT OF THE OPTICAL APPROACH TO SETI
On this page we summarize the most important arguments advanced by Microwave SETI
researchers as to why Optical SETI is vastly inferior to the microwave approach to SETI.
We believe a very convincing case is made here that these objections to lasers are
invalid - that searches for ETI signals are far more likely to be successful in the
The microwave objections to the optical approach are listed below. Click on the
"Arguments" to see details of these objections and why they either are not true
or of little consequence.
Finally, at the bottom of this page we state the one reason why lasers are vastly
superior to microwaves for interstellar communications. This one reason alone should have
been sufficient to have caused the main thrust of SETI researchers to be in the optical
regime. That it is not on this planet is a paradox!
Uplink gain has to be limited at optical wavelengths.
LASERS ARE VASTLY SUPERIOR FOR SETI AND INTERSTELLAR COMMUNICATIONS BECAUSE:
They are the only electromagnetic means by which wideband information can be conveyed
across thousands of light years without interstellar dispersion and scintillation effects
corrupting the signal. This is not withstanding the issue of the increased signal-to-noise
ratio capabilities of lasers.
Because different frequencies propagate at differing velocities (dispersion) and the
signal will suffer significant frequency-selective fading (scintillation) at microwave
frequencies, only optical carriers have the means of conveying uncorrupted wideband
Visible laser frequencies are about five orders of magnitude higher than microwave
frequencies, and thus, the corresponding percentage modulation bandwidths at visible
wavelengths are five orders of magnitude smaller than at microwave wavelengths. On these
grounds alone, the bandwidth capability of lasers is far superior. The argument for
infrared lasers is also just as powerful.
This is probably the one advantage of lasers that dictates there use for SETI and
interstellar communications. All the other advantages are just "icing on the
The SETI Community must address the issue of where we expect to find the wideband data
channel. There doesn't seem much point in having the attention-getting beacon channel in
another part of the electromagnetic spectrum. The beacon and wideband channels are more
likely to be placed side-by-side in the spectrum or multiplexed together in the same part
of the spectrum to form a composite signal.
We challenge the Microwave SETI Community to prove that interstellar laser
communication systems are inferior to corresponding microwave systems due to limitations
set by dispersion and scintillation. If they cannot prove this, then they have lost their
arguments for microwaves being superior.
We call for a detailed comparative analysis of the relationships governing the levels
of interstellar dispersion and scintillation effects throughout the entire electromagnetic
spectrum, and in all directions in space. This analysis may even determine preferred or
"magic wavelength" regimes in the visible spectrum.
The answer to this challenge and question should govern the future main thrust of SETI
on this planet.