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 optical spectrum.

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.

• Argument 1

Photon noise much higher than thermal noise at optical wavlengths.

• Argument 2

Backround noise from ETIs' star is much higher at optical wavelengths.

• Argument 3

An all-sky survey not possible at optical wavelengths.

• Argument 4

Technology for ETIs more expensive at optical wavelengths.

• Argument 5

Lack of magic frequencies at optical wavelengths.

• Argument 6

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 signals.

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 cake"!

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.