Can Anything Travel Faster than Light Speed?
No “thing” (including particles) can travel faster than light speed, but some “non-things” can. In both ways “nothing travels faster than the speed of light”.
What this means is that, nothing with mass can travel faster than the light speed constant (i.e. “the speed of light, in a perfect vacuum, measured from an inertial frame as a constant with an exact value of 299,792,458 m/s.”)
Despite this, under special conditions, such as during the big bang when space expanded faster than light, or in cases where light is slowed down, this rule can sort of appear to be broken (see for example: 4 Things That Currently Break the Speed of Light Barrier).
However, even in these cases, there is always a caveat that explains what is happening. Consider the following two examples:
- In the Big Bang, it was “nothingness” (AKA empty space) that expanded faster than light. Thus, that doesn’t truly break the rule.
- In cases where light is slowed down, light is no longer traveling at its constant speed, and even sound can travel faster than light in these conditions. Thus, this doesn’t break the rule either.
Rules For Light Speed (Why Nothing Can Travel Faster Than the Light Speed Constant)
With the above noted, rules that apply to light speed include:
- Light speed [in a perfect vacuum] is a constant speed and the maximum speed of the universe.
- Pure massless energy (like a photon) always travels light speed (in a true vacuum).
- However, massless energy doesn’t always travel its constant speed in practice (as it is often impeded in some way; there are no perfect vacuums in the physical universe).
- Nothing with mass can travel as fast as the speed of light, or faster (according to relativity).
- Nothing made of the fundamental particles from the standard model (i.e. no information) can travel faster than light speed.
- However, the absence of information can travel faster than light speed.
This means a shadow or the expanding universe can travel faster than light, but a photon or a spaceship can’t as far as we know.
TIP: This can all be confirmed by understanding the standard model of particle physics, the physical constants (like light speed or the Planck), and relativity. The universe has limits (just like one uses for calculus and other mathematics), and the laws of physics depend on constants and limits.
TIP: Spooky action at a distance is strange, but it isn’t breaking the speed barrier, it is instead explained by quantum entanglement. In this same vein, quantum superposition doesn’t technically break the speed limit either. So, empty space expanding, the slowing down of light, the speed of non-information, and that which is explained by entanglement and superposition, none of these break the rule!
What is the Speed of Light?
The key to confirming the above is is found in understanding what light is and how light speed relates to it. We already covered this a bit above, but let’s reiterate one more time before moving on.
The speed of light is the constant and only speed that pure massless energy travels in a vacuum (the max speed of the universe). The only thing light can do on its own is move at light speed in a single direction forever (which is 299,792,458 meters per second or approximately 3.00×108 m/s).
The Speed of Light is NOT About Light | Space Time | PBS Digital Studios.
TIP: Light is layman for “electromagnetic radiation” (visible light is only a small part of the electromagnetic spectrum). Light speed is one of a few universal constants. The others are the Planck unit and Gravity. All constants are derived from the constant nature of mass-energy.
Information can’t travel faster than light speed. A massless energy particle (like a light photon) will always travel at light speed in a vacuum, as measured in an inertial frame (a frame of reference moving at same speed as the object being measured),
In a non-vacuum one can slow down photons with a crystal, or trap a photon in a quantum computer, but one can never get a photon to go faster than the max speed of the universe (light speed). This is because light speed is the speed that everything is happening at in the universe, and things can’t happen faster than they actually happen.
This video explains the speed of light being constant without math. It appears heady at first, but give it time. Toward the end, it really earns it’s salt as an easy to understand the model of light’s behavior. See references section below for the explainer website.
TIP: Given the fact that the speed of light is a constant speed at which things happen, we can think of it as “the speed of causality” or the speed at which things take place in the universe. We can use light to get standard agreed upon units with which to measure time and distance such as “light years.”
The Absence of Information Can Travel FTL
That said, the absence of information can travel faster than light. If I wave my hand in-front of a very bright light that casts a very large shadow, the shadow can move faster than light… as the shadow is not an actual thing, but rather the absence of a thing (no “thing”).
The expansion of space also breaks the limit. As space expands, two galaxies traveling away from each other far enough away from each other will move much faster than the speed of light. The universe is “Expanding faster than the speed of light” and the farther away objects are from each other, the faster they expand away from each other… but expansion isn’t a “thing” itself, and so it’s not information traveling faster than light.
Special Relativity and Light Speed
In technical terms, special relativity says a “thing” with non-zero rest mass needs infinite energy to accelerate to light speed. So non-massless energy can’t travel faster than light. That said, special relativity doesn’t explicitly forbid traveling faster than light, it just implies:
- Light speed is the maximum speed of the universe.
- Light speed is the speed at which all massless energy particles always travel. All the fundamental particles that make up the universe are massless energy particles, which travel at light speed.
- Time as we know it stops at light speed.
- Light speed can be thought of as “the speed of causality” the speed at which casual relationships happen in the universe. All other time outside time measured by light is relative.
- Crunching the numbers, only a special particle called a Tachyon can travel faster than light. In a vacuum, it would always travel faster than light, and never go slower.
The result is that light speed particles always travel at light speed. Those particles interact to form systems with mass, which are all the objects in the universe. The systems with mass require infinite energy to go light speed; theoretically the object is ripped apart and becomes pure massless energy again, like a black hole.
Given all the above, we conclude that while relativity allows for it, light speed travel for non-zero rest mass objects is not something that seems actually to happen in our universe and certainly, faster than light speed travel only exists as an effect or perception (not as an actual thing).
Despite this, we can theoretically do things like “warp spacetime” to create wormholes which could allow us to use the way gravity theoretically curbs spacetime to get around the rule that things can’t move faster than light. This isn’t discussed here, and this isn’t the same as “faster-than-light.”
TIP: Understanding E=MC2 is understanding light speed and why things can’t go faster than it.
How Can Non-Things Travel Faster Than Light?
Light can’t travel faster than light speed, and objects with mass can’t travel light speed, but their effects (like a shadow) can (because effects of a thing aren’t themselves things).
What is the speed of dark? It is the same as the speed of light (as dark is light canceling itself out). That said, shadows can move faster than light because a shadow is not a thing, it’s the absence of a thing.
TIP: Saying “nothing travels faster than the speed of light” is essentially correct, but it’s also semantically confusing. The only thing that can travel faster than light is a non-thing (like a hole or shadow). Best then to say information can’t travel faster than light speed, this is always true. The maximum speed for energy and casual relationships in the universe is light speed. In fact, this is the only speed the massless energy particles that every “thing” is made of can travel.
But Didn’t they Discover Things That Travel Faster than Light Speed?
You may have heard about tachyons, which are theoretical particles that travel faster than light, or spooky action at a distance (quantum entanglement), or FTL neutrinos (see Superluminal Neutrinos, as requested by a reader). While all of these are very interesting subjects, the fact still remains, no particle has ever been confirmed to travel faster than the speed of light. From what we know, we only see things moving faster than light from a relative non-resting frame (if we are moving relative to an object and start measuring relativistic mass-energy).