Humans have explored the globe, traveled faster than the speed of sound, and gone to the Moon. Humans have learned secrets of the universe that no other species of our planet could possibly comprehend. Surely it will be only a matter of years, or perhaps decades, before humanity will begin traveling to the stars.
How hard can it be? We were told in the early decades of the twentieth century that no aircraft would ever be able to exceed the speed of sound. Yet on October 14, 1947, Chuck Yeager became the first person to do exactly that. And now aircraft repeat that astounding feat with routine aplomb. Surely breaking the speed of light barrier will be no different. Once we learn how to do it, we’ll build spacecraft that will flip into faster-than-light mode (FTL) as readily as a car switches into overdrive.
Before we attempt to understand the notion of FTL, we should first try to understand just how vast our galaxy truly is. The Milky Way galaxy is somewhere between 100,000 and 200,000 light years in diameter, and the Earth is about 27,000 light years from its center. Hence the Earth traverses an orbit roughly 170,000 light years in circumference for each of its 225 million year revolutions about the galaxy’s center. A spacecraft traveling at the speed of light would therefore require 170,000 years to make one complete circumnavigation of the Earth’s orbit. And that allows no time at all for either acceleration or deceleration. There would therefore be no time in that 170,000 years to stop and smell the flowers on any of the millions of planets one might encounter along the way.
The speed of light is about 186,000 miles per second. That’s about 669,600,000 miles per hour. The fastest human created spacecraft as of this writing is the Parker Solar Probe, which has used the tremendous gravitational field of the Sun to accelerate to 330,000 miles per hour. That is less than 0.05% of the speed of light! At that rate it would take the Parker Solar Probe more than 340 million years to traverse Earth’s orbit. That’s actually longer than it takes the Earth to make the same circuit!
Those who dream of galactic empire must confront the hard realities of the sheer size of our galaxy. The first galactic explorers will certainly want to chart the star systems they encounter– taking note of the habitable planets they discover, as well as those which are already inhabited. And they will undoubtedly need to refuel along the way. To stop long enough to survey a planet will require deceleration and acceleration– all of which will cost fuel, and time. To conduct such a reconnaissance mission at the measly rate of the Parker Solar Probe would ensure that by the time the explorers return to Earth, human civilization would have evolved into something vastly different than what it was at the time of departure.
Information is key to maintaining an empire. Desperate events in distant quarters may require a speedy reallocation of resources. To simply know that there is a problem requiring attention at the far end of a galactic empire would require a messaging system that can traverse the intervening distance in a reasonable time. On a galactic scale, that means the signal must travel faster than light. If the message implies that resources must be reallocated to address the issue, then those resources must themselves be transported in a reasonable time. “Reasonable” in the context of a galactic scope means within minutes or hours, not millenia.
Let’s imagine that the Earth is the seat of a galactic government, and that on the opposite side of the galaxy, about 54,000 light years distant, the local governor of a planet calls for aid in putting down a rebellion. At the speed of light it would take 54,000 years for the governor’s call to reach Earth. That’s not an actionable time.
But even at 54,000 times the speed of light it would still take one full year for the governor’s call for aid to reach the seat of power. In most cases news that arrives a year after the fact is too late to be useful. To reduce the travel time to one hour, the message would have to travel 8,766 times faster still– or 473,364,000 times faster than light!
Science fiction stories of galactic empire routinely mention traveling at two, three, four, or even ten times the speed of light, as if that were so astonishingly fast that it should be possible to travel anywhere in the galaxy in just a matter of hours. But in fact it’s not even remotely fast enough to hold an empire of galactic dimensions together.
If the sound barrier could be broken, why can’t we break the speed-of-light barrier? The reason is that the two barriers are of two completely different categories. The sound “barrier” was a concern raised by materials engineers of the times that no airplane fuselage could be designed to withstand the terrible shock wave that would be created by exceeding the speed of sound. It was chiefly a problem of materials.
But the speed-of-light barrier is altogether different. The two foundational principles of Einstein’s Special Theory of Relativity are that (a) all signals exchanged throughout the universe propagate via electromagnetic radiation (including visible light); and that (b) the speed of light is constant for all observers, regardless of their relative velocities. These two seemingly innocuous assertions have tremendous ramifications– one of which is that no physical object can travel faster than the speed of light. More than that, it would take an infinite amount of energy to accelerate a physical object to the speed of light!
But the weirdness of Einstein’s Relativity doesn’t stop there. As an object accelerates, its internal clock slows down. And in fact the clock of an object traveling at the speed of light actually stops completely. A beam of light experiences no time! So even if you could accelerate to the speed of light, your clock would stop. You would never age– but you would also never have any more thoughts. And consequently you could never observe the stars or planets you pass by, never plan where to go next, never decide to slow down or stop.
These strange consequences of Einstein’s simple claims have been repeatedly tested. Relativistic principles even had to be considered in the design of the Global Positioning Satellite System. So even a cell phone provides daily proof of the fact that Einstein was right when it simply accesses the GPS system.
Is there any loophole anywhere in Einstein’s reasoning? Doesn’t Quantum Entanglement mean that messages can be transmitted at essentially an infinite speed? The inflationary period of the Big Bang theory is a time when the universe expanded at more than 1021 times the speed of light. Doesn’t that say that Einstein was wrong?
Quantum entanglement isn’t likely to provide a useful solution as it is only capable of propagating quantum states. Two particles are said to be entangled if their quantum states are strongly correlated. In this case knowledge of one particle’s state instantaneously conveys knowledge of the other’s. But if one particle is disturbed, information about that disturbance can only be conveyed from one particle to the other at the speed of light. So although entanglement seems to offer the promise of instantaneous transmission of information, it does not support the notion of instantaneous transport of a physical force at a speed faster than light. And therefore it doesn’t really provide a way to transport a physical object from one location to another at a faster-than-light velocity. At least, not as presently understood.
As for the theory of inflation, the mechanism that would have triggered inflation isn’t known. It has been hypothesized by the advocates of the inflationary theory that gravitational attraction could have been flipped to repulsion in the very first instant’s of the universe’s existence by the presence of an extremely small amount of “exotic matter.”
So all we have to do is just create some of this “exotic matter” and we should be able to go as fast as we want, right? Uh, well… The current model of inflation only requires an extremely minute amount of exotic matter (relative to the total amount of matter in the universe) to cause the entire universe to expand exponentially. It doesn’t seem like it would be a good idea to create such a volatile material without knowing exactly how to handle it– unless you don’t mind blowing up the entire universe as part of your FTL experiment.
The only way out of the dilemma posed by the Theory of Relativity, as I see it, is to reconsider the first of Einstein’s two pronouncements– that all signals throughout the universe are conveyed by forms of electromagnetic radiation. Consider the human body. Our bodies are comprised of materials that consist of molecules, which are built up from atoms held together by atomic bonds. Atomic bonds are based on electromagnetic attraction. The present day theory of electromagnetic interaction, Quantum Electrodynamics, holds that electromagnetism is the result of the exchange of photons between charged particles. That exchange of photons happens at the speed of light, c.
But what if there is some other type of physical signal that can travel at a speed much faster than that of light? Let us suppose, for example, that there is another type of matter, call it FTL Matter, that is able to travel at speeds much greater than that of light. Suppose further that interactions between particles of such matter are propagated by some type of radiation that also travels at a speed much faster than the speed of light– call it c’. Now let’s go back to the primary assertions of Special Relativity and reframe them in terms of FTL Matter:
(a) All signals exchanged between particles of FTL Matter travel at the velocity c’.
(b) The speed c’ is constant for all observers comprised of FTL Matter in the universe.
From these two fundamental assumptions a new set of Lorentz transformations can be derived that involve c’ rather than c, and in all other respects the physics of FTL Matter would parallel those of ordinary matter. And this would establish a new cosmic speed limit c’, rather than c, for all FTL Matter.
So can we use some of this FTL Matter for FTL travel to distant parts of the galaxy? Perhaps the method would be to build an engine that consumes FTL Matter fuel, using the laws of FTL Matter physics, to propel a spacecraft made of ordinary matter to velocities close to c’. Sounds enticing, but at present nobody knows if there is any such thing as FTL Matter, or if the idea of constructing an FTL Matter engine is even remotely feasible.
Breaking the speed-of-light barrier is a completely different category of problem from that of breaking the sound barrier. This isn’t simply a problem of materials engineering, though there may very well be a serious question as to what happens to ordinary matter when it is accelerated to a velocity greater than c. The real problem is at the most fundamental level of the physics of our universe. Thus far, the Special and General Theories of Relativity have survived every test to which they have been subjected– and so they represent the very best knowledge we presently have of how our universe works.
I realize that this isn’t what fans of science fiction want to hear. They want to believe that we will soon be exploring the length and breadth of the galaxy, and will soon be trying to figure out how to travel to other galaxies beyond our own. Given what we presently know about the way matter behaves in our universe, it seems extremely unlikely that FTL travel will ever be possible. And that means that exploration and colonization of the Milky Way galaxy will proceed at a slower-than-light speed and will therefore take millions of years.
Copyright (c) 2022, David S. Moore
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