Recent Hubble measurements suggest that the universe isn't as grainy as it should be. This may sound paradoxical, but it seems to challenge our basic notions about this reality we call our universe.
One of the principal goals of science is to understand the wonderful diversity in the natural universe in a unified way. The quest for a Grand Unified Theory, a "Theory of Everything," is the ultimate frontier of physics, the most fundamental of all our sciences. Some of the greatest achievements of science have been advances toward this goal.
The unification of terrestrial and celestial mechanics by Sir Isaac Newton was one of the great achievements in the 17th century. The eloquent theories of electricity and magnetism by James Clark Maxwell in the 19th century have impacted every aspect of our modern lives. Space-time geometry and the revolutionary theory of gravitation by Albert Einstein in 1905 to 1916 have ushered in our ventures into space itself. The unraveling of chemistry and atomic physics through the advent of quantum mechanics in the 1920s continues to turn our scientific understanding upside down. While this emergent field of discovery has ushered in the age of lasers and microcircuits, it has also opened up a Pandora's box of enigmas and contradictions that have shattered the very foundations of our understanding of reality.
Four Basic Forces
There are four basic forces in nature, and they account for all the dynamics observed throughout our physical universe. They are gravity, the electromagnetic force, and the "strong" and "weak" nuclear forces.
Gravity causes an apple to fall to the ground, keeps our feet on the floor, and binds our Solar System together. It keeps the earth and the planets in their orbits, prevents the stars from exploding, and guides the galaxies in their motions. While easily overcome in the short distances we normally encounter, it is the dominant factor in the dynamics of the universe and its major components.
The electromagnetic force holds the atom together and determines the structure of the orbits of the electrons. Thus, it governs the laws of chemistry. Its various forms include x-rays, radio waves, and light. It can overcome gravity on the earth, and it can dominate the other forces down to about the size of the nucleus of the atom. That's where the two other "nuclear" forces take over.
The "Strong" Nuclear Force
The strong nuclear force binds together the protons and neutrons in the nucleus of the atom. The balance between the strong force and electromagnetic force limit a nucleus to about 100 protons, which thus determines the "Periodic Table" of the elements. The energy released by the strong nuclear force is substantially greater than the electromagnetic (chemical) force, so the explosion from atoms being split apart is substantially greater than one from chemical explosives. Thus, the strong force causes the stars to shine and the sun to warm our earth. It, too, is essential for life.
The "Weak" Nuclear Force
The weak nuclear force governs atomic instability and radioactivity. It is what causes the disintegration of heavier nuclei. It can create heat, such as that produced in the decay of radioactive elements in the earth's core and in a nuclear power plant.
The Quest for a Grand Unified Theory
The pursuit of a Grand Unified Theory (GUT) is the attempt to link together the four forces of physics and the fundamental constants - c, the velocity of light; e, the charge on the electron; h, Planck's constant; and, G, the gravitational constant. One of the most important lectures in mathematics was given on June 10, 1854, when Georg Riemann unveiled his technique of metric tensors, which paved the way for dealing with hyperspaces: spaces of more than three dimensions. It took over 60 years, but this opened the door for Albert Einstein's famous Theory of Relativity in 1915. While grappling with his attempt to resolve the paradoxes of space and time, he developed four-dimensional space-time. Tragically, he went to his death still frustrated with his inability to broaden its application to the area of quantum physics.
In another 40 years, Kaluza and Klein, exploiting five and larger hyperspaces, extended the application of hyperdimensional analysis to include light and supergravity, and in the 1960s, the Yang-Mills fields succeeded in including electromagnetic and both nuclear forces.
The current challenge is to somehow include gravity into the milieu. The latest candidates are hyperspaces composed of superstrings, P-branes, and other theoretical devices.1 The latest count invokes at least 11 higher dimensions in the mathematical models that attempt to tie together the Laws of Physics.2
The current theory of elementary particles and forces is known as the "Standard Model" of particle physics, and it has achieved a unification of electromagnetism with both the "strong" and "weak" nuclear forces. It is when the microcosm of quantum physics and the macrocosm of gravitational forces are embraced together that profound difficulties arise.
The Standard Model and its close cousin, the Big Bang theory, are both facing challenges from many quarters, so we won't try to deal with them in this brief review. (I'm reminded of the shock that the participants had in the movie, The Thirteenth Floor, when they discover that they are merely participants in a simulated universe. What makes that particular piece of entertainment so provocative is that we, too, now discover that we are also participants in a digital simulation! Quantum physics reveals that our entire reality is a digital simulation of sorts.)
Walking the Planck
When one brings quantum mechanics into attempts to unify the laws of physics, Planck's constant is found to define the "fuzziness," or the "grain size" of the universe.3 (Thus the smallest meaningful length is (Gh/c3)1/2 = 10-35 meters. The smallest time increment of time is the Planck time, 10-42 seconds, the Planck mass, (hc/G2)1/2 = 1019 Gev, etc.)
The big surprise was that light photons, though massless, carried momentum and energy - and photon energy and momentum were quantized; that's why they call it "quantum physics." When atoms emit photons, they do so only at discrete wavelengths. The energy of photons can be calculated from the simple formula, E = hf = hc/' where h is Planck's constant, c the velocity of light, f the frequency of the light and ', the wavelength.
Sharp Images Blur Physical Concepts
Physicists' notions of the universe could now be in further trouble. New measurements from the Hubble Space Telescope indicate that space is smooth, not grainy.4 Without graininess, our current theories predict that the Big Bang was infinitely hot and dense - tough to explain, to say the least. Two groups have peered at distant stars and galaxies, and have discovered a pin-sharp picture. This, they claim, is at odds with quantum physics' prediction that space, time and also gravity are split into pieces at the smallest scales, like the pixels of a photograph. If this were the case, the picture should have been blurry, they argue. "The theoreticians are very worried," says Richard Lieu of the University of Alabama in Huntsville, a member of one of the teams. "There could be quite a bit of missing physics to be found."5
At stake is the issue of whether we can reconcile the two pillars of modern physics: quantum theory, which describes how matter behaves at the scale of atoms, and general relativity, which relates space, time and gravity at larger scales. "You don't see anything of the effect predicted," agrees Roberto Ragazzoni of the Astrophysical Observatory of Arcetri, Italy. 6 He and his colleagues got similar images to Lieu's team, but with a different instrument, and trained on different objects.
"These observations are very interesting and potentially very important," agrees theoretical physicist John Barrett of the University of Nottingham, UK. "Any theory of quantum gravity is going to have to take them into account."
The new observations would seem to cast doubt on the existence of two quantum physics quantities: the Planck length and the Planck time. In theory, these are the smallest measurable units of space and time. Physicists calculate that the Planck length is slightly more than one trillion trillion trillionth of a meter. This is the distance that a photon, moving at the speed of light, can travel during the Planck time: 5x10-44 seconds.
We can measure the Planck time, reasoned Ragazzoni and Lieu, by looking at distant objects. As a beam of starlight hops towards us through countless Planck times, its speed varies. This would smear the beam out so that different parts would arrive at different times and distort our picture of where it came from. The longer the journey, the bigger the smear. Ragazzoni's team adapted the theory of the Planck length to predict the amount of distortion they should see. But when they used the Hubble telescope to look at an exploding star about 42 million light years away, and a galaxy more than five billion light years away, they saw no blurring.
Theoreticians have suggested two arguments as to why a universe that is pixilated might still look sharp. One is that time and space might vary together at the Planck scale, keeping beams of starlight in their original formation. The other is that the wobbles might reflect the Planck length squared- about 10-60 meters - making the smearing undetectably small.
It is clear that further study will be required, but it is disturbing that our foundational concepts seem to be on quicksand.
As we read of various theories and conjectures - especially in the cosmological realm - let's keep in mind that about 95% of the mass of the universe is "missing!"7 The known visible universe accounts for about 5% of the mass and the search for the "missing matter" continues. Red dwarfs, once considered a possible explanation, have been ruled out through experiments with the Hubble Telescope.8
Other alternatives, which also remain purely conjectural, supposes the existence of bizarre particles or objects like "weakly interacting massive particles" (WIMPs) and "massive compact halo objects" (MACHOs). If explanations in terms of ordinary matter composed of baryons (protons, neutrons, etc.) prove impossible, the only remaining alternatives would involve revising our basic understanding of the laws of physics.
It is extremely important to realize that our entire knowledge of the physical universe remains embarrassingly incomplete. We need to maintain a deep humility as we explore the current perceptions of the universe, and as we encounter the expansive conjectures of that speculative sphere of interest known as cosmology. There will always be those who enjoy drawing "vast conclusions from half-vast data!" We recall God's science quiz He gave Job:
Who is this that darkeneth counsel by words without knowledge? Gird up now thy loins like a man; for I will demand of thee, and answer thou me. Where wast thou when I laid the foundations of the earth? declare, if thou hast understanding. Who hath laid the measures thereof, if thou knowest? or who hath stretched the line upon it? Whereupon are the foundations thereof fastened? or who laid the corner stone thereof; When the morning stars sang together, and all the sons of God shouted for joy? -Job 38:2-7