Light is funny stuff. You can think of it as a particle, called a “photon,” traveling in a wave-like fashion, undulating up-and-down (or, to be fair, from side to side) along its established path. Or you can think of it as the wave itself, but with a separately measurable quantity, or “quantum,” of energy equivalent to a photon’s basic properties. Light has all the properties of both tiny particles and elongated waves.1
Light comes in many wavelengths, which are the distance from one “upward” swing of the wave to the next. That distance from peak to peak defines its frequency. The closer the peaks are, the more energy the photon or quantum carries.
Light is not just the visible light by which we see the world—sunlight, moonlight, electric light—but all forms of electromagnetic radiation. These include the long wavelengths of radio and television signals, which vary between 10 meters (about 30 feet) and one meter (about a yard) from peak to peak. Next up the energy scale come microwaves of about one centimeter (hundredth of a meter) peak to peak, which are useful in both long-distance communications and rapid cookery. More energetic still is the energy we feel as heat from a fireplace or a glowing filament, which falls in the “infrared” (or “below the red”) wavelengths of about one micrometer (millionth of a meter). Above that lies the deep end of the visible spectrum, the red end at about 700 nanometers (billionths of a meter), which then proceeds through the various colors of light you can break out with a prism to the deep blue or violet end of the spectrum at about 400 nanometers. Beyond that is the “ultraviolet,” at between 100 and 10 nanometers. And if you go further into the shortest measured wavelengths you get the x-rays at about 1 nanometer, energetic enough to pass through soft materials like flesh and blood but not through denser bones, and then the gamma rays at one ten-billionth of a meter, a unit called an ångstrom after the Swedish physicist, which are small enough and energetic enough to knock around your DNA and make life-changing mutations.
Since all light travels at the speed of, well, light, the amount of energy in a burst of electromagnetic radiation—whether it originates as radio and visible light waves coming from the fusion of a main sequence star like our Sun, or as X-rays from a rapidly spinning pulsar—does not affect its speed, only its wavelength. The speed of light or any electromagnetic radiation remains constant.2 And its energy level remains unchanged no matter how far the light has traveled, nor how long it has been in transit. Light does not “get tired” and lose its original energy.3 This is because, according to Einstein’s theory of relativity, for anything traveling at the speed of light, time has essentially stopped. The only way it can lose energy is to interact with matter along its route.
We live inside a vast machine called the universe. Think of a microbe sitting on the face of a gear inside an old watch—or rather, something much smaller than a microbe sitting on a gear in a clockworks much larger than Big Ben’s. The gears, the escapement, the hands of the clock are all moving. But, from the perspective of our microbe’s busy little life, the movement is so slight, the action so slow, that the clock appears to be frozen in time, motionless, even immovable.
Like that microbe on a gear, we sit on the face of our own planet. We can sense a bit of motion from the Sun’s rise and fall in the sky, the cycle of days, the motions of other planets and their satellites against the night sky, and the turning of the background star field throughout the year. But the rest of the universe—including those fixed stars—might have been painted on the inside surface of a distant sphere. Not until about four hundred years ago did we finally figure out that the Earth was not the center of all this motion but was itself moving like the other planets around the Sun. And not until about a century ago did we figure out that some stars were near to us, distant suns moving in a system called the Milky Way, while some of those bright patches in the night sky were actually other systems of stars, called galaxies, with their own proper motion. We now estimate that we live in a universe containing between 100 to 200 billion galaxies, each containing—if the current estimate of our own Milky Way is accurate—between 200 and 400 billion stars.
All of them are in motion. But the movement is so slight from our perspective—a microbe sitting on the face of a gear far removed from the real action—that we must detect this motion by means other than direct observation.
One such means is by measuring the light coming from distant galaxies, generated by stars which—because of the quality of their light and their occasional explosions—we believe to be similar to those in our own galaxy. In all of these distant stars, the light is shifted somewhat along the normal spectrum. In most cases the light has appeared to lose energy and shifted to the red in proportion to their distance.4 Since, as noted above, light cannot “become tired,” something else must be going on. Astronomer Edwin Hubble proposed in 19295 that the red shift was due to the Doppler effect: the light was dropping in pitch, like a locomotive whistle falling off as the train moves away from us, because the universe is actually expanding. That’s one piece of evidence.
If the universe is expanding, then at one time it must have been smaller. In fact, if you calculate backward from that rate of expansion, about 13 billion years ago it must have had almost no dimension at all. So was born the Big Bang theory: that the universe began in a single explosion of an infinitely dense, infinitely hot piece of matter, smaller than a proton, which contained all the mass of those hundreds of billions of galaxies each containing hundreds of billions of stars, plus the stuff we cannot see in other galaxies like dust, asteroids, planets, and brown dwarf stars. The Big Bang theory—which today is accepted as the one true origin story—is an inference from General Relativity and Hubble’s examination of starlight.
Then, in 1965, two Bell Labs engineers working on a microwave antenna in New Jersey that was designed for radio astronomy and satellite communications, Arno Penzias and Robert Wilson, discovered an annoying hum. It was a microwave signal of such low frequency that it equated to a temperature of 3.2 degrees Kelvin, barely above the absolute freezing point of all matter. It was a bit of static that no amount of tuning or antenna cleaning could eliminate. They suggested that the hum was the residue of the energy released in the Big Bang, now red shifted almost completely off the scale.6 That’s the second piece of evidence.
Since then, maps of this background radiation covering the entire sky—made first by NASA’s Cosmic Background Explorer (COBE) satellite between 1989 and 1996, then refined by the Wilkinson Microwave Anisotropy Probe (WMAP) from 2001 to 2010, and now further refined by the European Space Agency’s Planck probe in 2013—have shown variations which suggest how denser areas of that radiation might have formed into galactic groups. Analysis of the data also support the contention that the universe not only expanded from a single point but also that, at one time early in its growth, the universe inflated rapidly to yield the dimensions we can perceive today, and further that the expansion is now accelerating under the influence of some repulsive force that physicists call “dark energy.”
But, as microbes sitting on a distant and relatively unimportant gear in the clockwork, all of this activity must be inferred from the analysis of starlight and radio waves, using a great deal of human-created mathematics and a bit of human imagination. I’m not entirely comfortable with this commonly accepted origin story. It’s probably a true interpretation of the evidence. And I admittedly haven’t made a lifetime study of the more esoteric aspects of cosmology and mathematics to either confirm or deny it. But I maintain there is also much we still don’t understand about three of the underlying components of the story: the exact nature and structure of empty space, of time, and of the binding force that mediates between them, gravity.7
Still, I will note some oddities about the hypothetical explosion represented by the disintegration and scattering of the infinitely dense, infinitely hot8 particle at the center of the story of our universe:
First, the Big Bang may not necessarily have resulted from conditions of incredible temperature and pressure. When a spacecraft vents wastes into supposedly structured but empty space—a vacuum—it only takes 14 pounds of pressure per square inch inside the cabin to create a fairly energetic eruption. Would not the introduction of even a small amount of structured material into the unstructured nothingness of the pre-Bang void result in an infinite-seeming explosion?9
Second, the Big Bang may not even have been hot. When gas under pressure expands into space, that expansion actually cools the molecules, because their internal energy is used to spread them over a larger volume. You can feel this when you put your hand into an aerosol spray or the discharge of a CO2 fire extinguisher. Why would the Big Bang have operated differently? The Big Bang would have been a cold event.
Third, the Big Bang may not have had much to do with events in the supposedly “structured” space we encounter today. Until space was formed by the addition of matter, adding dimension and distance to the ultimate void, time would not have been operable. The starting point of the Big Bang would have been both timeless and dimensionless. If there is no distance and no time, then speed—which is a function of the two measurement systems working together—cannot exist. So to describe the speed of the universe’s initial expansion at the instant of the Big Bang or during its inflationary period immediately afterward is meaningless. To quote the old joke, “Time is God’s way of keeping everything from happening at once.” But in a dimensionless non-space, everything does happen at once, which is really the same as not happening at all.
Fourth, the Big Bang might not have occurred anywhere in particular. To understand this, we need a thought experiment from everyday life. Imagine four people sitting at a card table on the fifty yard line of a football field. Now a bomb under the table explodes and throws two of them off to the sidelines and two of them back to the twenty yard line at either end of the field. If you asked each person where the bomb was, he would look around at the chalk lines in the grass, point to the fifty yard line, and say, “Over there!” Now imagine the same four sitting at a table in a dark room of unknown dimensions. The bomb goes off and throws everyone an unknowable distance in an unknowable direction with no floor to record the impact of their landing. Ask each person where the bomb went off, and he would point to his feet: “Right here!” Without a reference for the origin in space-time coordinates, the original Big Bang was “right here” for every point in the newly expanded universe. Right in my back yard. Right here between my fingertips.
I accept that the Big Bang is the most logical explanation of the phenomena of radiant energy that we see around us today in the forms of starlight and the microwave background. The Big Bang’s initial properties are derived from our rigorous study of these phenomena and their analysis using advanced intellectual tools such as mathematics and theories based on observed laws of motion and thermodynamics. But I don’t have to like the Big Bang as an explanation, because it takes us into realms that are meaningless. The conditions of the Big Bang are at once infinite and nonexistent. They are conditions that not only can’t be studied but also can’t be understood in terms of the very laws of physics that suggest them.
My nose suggests we’re missing something. My hind brain suggests it’s something obvious. But I just can’t say what it might be.
1. In the classic dual-slit experiment performed by physicist Thomas Young (1773-1829) to prove the wavelike nature of light, shine a beam of focused light such as from a flashlight or laser onto a card that has one or more slits in it and then beyond that to a screen behind the card. If the card has just one slit, the beam shines on the screen at full intensity, although it is spread out in a diffraction pattern. But if the card has two slits side by side, the beams that get through it interfere with each other, creating a pattern of alternating light and dark areas on the screen.
A similar interference pattern occurs if an ocean wave rolls through a breakwater with two entrances: the collision of the two parts of the wave that make it through the breakwater interferes with the pattern of the original wave, making the water inside the harbor choppy and confused, resulting in separate wave pulses breaking against the inner wharf.
We can understand this interference if the light is made up of many photons all traveling in the same direction with the same original wavelength or intensity. But this interference pattern also appears if only one photon is passed through either slit. True, the particle hits the screen in only one particular place. But if you send many individual photons through the slits over a period of time, as if you were spraying them with individual machinegun bullets, the individual hits will eventually build up an interference pattern on the screen. Even though the individual photons exist at separate points in time, each one acts as if it was going through both slits at once and interfering with itself. I told you light was funny stuff.
If it helps, don’t try to think of photons as particles, like tiny bullets or BBs or bits of solid stuff like protons or electrons. After all, the photon has no mass, except for the momentum imparted by its energy. Instead, think of the photon as a quantum or discrete and measurable—although very tiny—“packet” of energy that moves in a wave-like fashion.
2. Depending on the medium, of course. The usual speed of light, at 186,282 miles per second (or 299,793 kilometers per second), is the speed in vacuum. It is slightly slower by a trivial amount when traveling through a transparent medium like air, water, or glass.
3. If light did simply “get tired,” such as by losing energy through collisions with stray atoms in interstellar or intergalactic space, then the light would be scattered and the images of distant stars and galaxies would appear with a fuzziness that no amount of optical resolution could fix. The “tired light” theory also does not account for the time dilations we can observe in the universe. For example, a nearby supernova may take 20 days to decay, but a similar type of star exploding in a distant galaxy may appear to take twice as long to go through the same process.
4. In a few cases, the light from distant galaxies has appeared to gain energy and shifted to the blue end of the spectrum. These blue-shifted galaxies do not invalidate the expansion of the universe. Instead, they are simply objects whose proper motion towards us cancels or reverses the red shift due to cosmic expansion.
5. Although the expansion of the universe is attributed to Hubble, who codified it as a law, he merely observed it and confirmed its existence from the observed red shift. The expansion was predicted by Einstein’s General Relativity, and the math was already worked out by Belgian priest and astronomer Georges Lemaître in 1927. Ten years earlier, American astronomer Vesto Slipher had observed the red shift of various stars and suggested it was related to their velocity. Everyone stands on the shoulders of giants.
6. Once again, they were only confirming something that others—in this case American scientists Ralph Alpher and Robert Herman—had predicted almost two decades earlier.
7. See my complementary blogs “Three Things We Don’t Know About Physics” fromDecember 30, 2012 and January 6, 2013.
8. To begin with, the concept of infinity and its attribution—as in “infinitely dense, infinitely hot”—should be a red flag. Infinity is a human construct, embedded in mathematics, to represent numbers that are simply beyond counting. We used to think the universe was infinite in time and space, but we now have a timing mechanism that gives it a very finite age, 13 billion years. (Not so big a number, when you consider that we now measure the national debt in trillions.) And the universe’s physical dimensions of length, breadth, and depth are “infinite” only because we cannot detect or derive a starting or an ending point. In those terms, every sphere from a billiard ball to the event horizon of a galactic black hole has an “infinite” surface area.
9. I use the word “unstructured nothingness” because in the current view of physics the vacuum of space appears to have structure. While the Michelson-Morley experiment of 1887 disproved the notion that empty space was filled with a universal and invisible substance called “luminiferous ether,” empty space still has something going for it. First, it has three dimensions with which we can orient ourselves and perhaps many more dimensions about which we can theorize but not yet detect. Second, space is presumed to be bathed in the fields associated with various quantum particles—electromagnetic fields, gravity fields, and so on. Third, it is presumed to be continually popping off pairs of matter/antimatter particles that appear and then silently, invisibly annihilate one another. And fourth, it appears to generate a “dark energy” that drives the expansion of the universe. Space may be empty but it is hardly uninteresting