Physics: unity in nature is still only fond theory

Physicists seeking unity in nature are encouraged by discovery of the so-called Z particle. But they are still far from their ultimate goal. Only one ''probable'' appearance of the Z has been reported (unofficially) from the European Center for Nuclear Research (CERN) at Geneva as of this writing. If confirmed, it will strongly support the so-called ''electroweak'' theory, which unites two of the four basic physical forces - the electromagnetic force and the ''weak'' force involved in some forms of radioactivity.

This still leaves gravity and the ''strong'' force that holds atomic nuclei together out of the picture.

Physicists' notions of how to include gravity are very speculative. But there are several theories that wed the electroweak and strong force. They follow the thinking underlying the now-successful electroweak theory.

This latter theory holds that electromagnetic and weak-force interactions between particles will be seen as different aspects of one kind of interaction at energies high enough to reveal the basic unity. The theory postulates four particles that mediate those interactions. They include the photon - the particle of light, which is massless. There are also three massive particles - two W particles, one with a positive and one with a negative electric charge, and a Z particle with no electric charge. The W was found at CERN early this year. Now the Z may have been found too.

In like manner, a Grand Unification Theory (GUT) maintains that electroweak and strong interactions will be seen as one at sufficiently high energies. Again , new particles are invoked to mediate interactions of the unified force. Physicists call them X and Y.

Unfortunately, the energy at which GUT unity appears is a thousand times greater than any foreseeable particle accelerator can attain. So physicists can't try to produce Xs and Ys in the laboratory. But they can check out a major GUT prediction. This is the prediction that the proton, the basic building block of atoms, may decay. Physicists had thought the proton is absolutely stable. But GUT implies that the proton can indeed transform in ways that allow spontaneous decay.

Protons would still live a long time - many thousand times a billion, billion , billion years on average. However, if one watches a mass of many protons - say a few hundred to a few thousand tons of iron or water - one should see a few protons decay within a reasonable time. This is what several experiments in India, Europe, and the United States have been doing. So far, they have negative or ambiguous results.

For example, a research team principally from the University of California at Irvine, the University of Michigan, and Brookhaven National Laboratory has been watching 10,000 metric tons of water since last July. Team member Lawrence R. Sulak, in a recent talk at the Massachusetts Institute of Technology, said several proton decays should have been seen by now according to the leading GUT prediction. The fact that none has been seen suggests a proton life greater than 650,000 billion, billion, billion years.

Sulak adds that, as the various experiments proceed, proton decay should show up within the next few years if the lifetimes predicted by present Grand Unifying Theories are correct. Thus the unifiers have only a little while to wait to see if they are on the right track. But even if one of their theories does work, what then of gravity? Until gravity is included, the goal of a single all-embracing theory of matter and energy remains elusive. Competition helps US sciencem

While many voices in the US bemoan ''loss of technical leadership,'' - and some call for more secrecy in research - Frank Press, president of the US National Academy of Sciences, welcomes the foreign competition.

In a recent editorial in Science, he explained:

''Many of the concerns in this country related to the health of science . . . stem from the pressures of being at the scientific frontier, at the top of a very slippery climb.

''Other countries are now climbing that slope. ... We ought to welcome the competition, for as long as we see to our own house, we will gain greatly from the scientific advances of other nations. ...

''If the United States ... is to gain from intensified competition, the essential requirements are open communication of science and the resolve to incur the costs of maintaining general excellence in basic research. Regarding open communication, . . . those that have the most to give have the most to gain. The strength of American science ensures our capability to benefit from progress in any field elsewhere.'' No word from Marsm

The US Viking Mars team has all but given up hope of hearing from the Viking 1 Lander on the Red Planet. They failed to raise the Viking radio transmitter May 5 and on May 13. According to the NASA-Jet Propulsion Laboratory, one more attempt will be made to contact Viking Saturday, May 21. If that fails the team will likely give up. India in spacem

India's space program has taken what its officials consider a major step forward with the successful launching last month of the 92-pound scientific satellite Rohini-II.

At this writing, the satellite was believed still to be working satisfactorily. But the most significant achievement was the successful performance of the Indian-developed launching rocket SLV-3. Having previously failed two of three development tests, the rocket now is considered ''operational'' by ISRO, the Indian Space Research Organization.

India plans to develop more powerful versions of the rocket. It intends eventually to orbit reconnaissance and communications satellites and to place a one-ton satellite in polar orbit.