The Universe Has A Speed Limit, And It Isn’t The Speed Of Light
“We believe that every charged particle in the cosmos — every cosmic ray, every proton, every atomic nucleus — should limited by this speed. Not just the speed of light, but a little bit lower, thanks to the leftover glow from the Big Bang and the particles in the intergalactic medium. If we see anything that’s at a higher energy, then it either means:
1. particles at high energies might be playing by different rules than the ones we presently think they do,
2. they are being produced much closer than we think they are: within our own Local Group or Milky Way, rather than these distant, extragalactic black holes,
3. or they’re not protons at all, but composite nuclei.”
If you were to try and travel as close to the speed of light as possible, you’d never get there because of Einstein’s relativity and the fact that you have mass. But even if you pumped an arbitrary amount of energy into you, you still wouldn’t get arbitrarily close to the speed of light. Instead, you’d find that there was a barrier or cutoff just a little bit below the speed of light: about 80 femtometers-per-second below the ultimate cosmic speed limit. That’s because the leftover glow from the Big Bang, the cosmic microwave background, exists no matter where you go, and prevents you from going any faster. Even if you beat that speed, it will knock you back down below it in short order.
There’s a speed limit for matter in the Universe, and it isn’t the speed of light. Come find out the details of why today!
How Come Cosmic Inflation Doesn’t Break The Speed Of Light?
“In an inflationary Universe, any two particles, beyond a tiny fraction of a second, will see the other one recede from them at speeds appearing to be faster-than-light. But the reason for this isn’t because the particles themselves are moving, but rather because the space between them is expanding. Once the particles are no longer at the same location in both space and time, they can start to experience the general relativistic effects of an expanding Universe, which — during inflation — quickly dominates the special relativistic effects of their individual motions. It’s only when we forget about general relativity and the expansion of space, and instead attribute the entirety of a distant particle’s motion to special relativity, that we trick ourselves into believing it travels faster-than-light. The Universe itself, however, is not static. Realizing that is easy. Understanding how that works is the hard part.”
It’s true that nothing can move faster than the cosmic speed limit, the speed of light, and that no two particles can move faster than light relative to one another. So how, then, do you explain the fact that during inflation, two particles that begin a subatomic distance away from one another are, after just a tiny fraction of a second, are then billions of light years apart? The answer is because special relativity only applies, strictly, to particles that occupy the same location as one another in both space and time. If they’re separated, then the Universe is under no obligation to be static, and space is free to expand and/or contract. You cannot figure your apparent motion with special relativity alone, but need to factor in the effects of general relativity as well. And that’s where things get really weird.
If you can understand it, however, the notion of how objects appear to recede faster than light suddenly starts to make sense. Come learn how inflation doesn’t break the speed of light after all!
Five Discoveries In Fundamental Physics That Came As Total Surprises
“It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”
It’s often said that advanced in physics aren’t met with “eureka!” but rather with “that’s funny,” but the truth is even stranger sometimes. Rather than the scientific method of: hypothesis, method, experiment, results, conclusion, revise, repeat, etc., many times throughout history, it’s been a series of surprise observations that have often led to our greatest leaps forward. When the speed of light was discovered not to differ when you moved with or against it, it was so revolutionary it was the only Nobel Prize ever awarded for a null result. When the gold foil experiment resulted in high-energy recoils, it surprised Rutherford so thoroughly it was the most incredible thing to ever happen to him in his life. The leftover glow from the Big Bang was discovered quite by accident; the neutrino was a crazy hypothesis that many abandoned; and the discovery of the muon, perhaps the most unexpected particle of all, literally was met with a cry of, “who ordered that?” from Nobel Laureate I.I. Rabi.
These five discoveries changed the course of physics forever, but they came as total surprises to practically everyone. Sometimes, the answer is in the place you least expect.
Comments of the Week #171: From light’s speed to proving Einstein right
“Science, just to be extremely clear, does not rely on one experiment to settle the matter, and then never perform the experiment again. No; we are constantly checking our results, gathering more data to improved precision, and looking for flaws in our predictions at the 10% level, then 1%, then 0.1%, then 0.01%, etc.
The story of scientific investigation is a story of ever-increasing precision and ever decreasing uncertainty, and one that I value and will keep telling, no matter what some (or many, or even most, sometimes) of the commenters here or elsewhere say. The scientific truth is too important, even if (and when) public opinion is against it. It’s why I’m here, and it’s what I’ve been doing — somewhat successfully, mind you — for over nine years now. In fact, when January rolls around, that will mark 10 years since the inception of Starts With A Bang. That we’re all here, thinking about the Universe and how it all works, is something worth celebrating, even when it’s difficult.”
Some of you caught me at the Star Trek Las Vegas convention this year, where thousands of Star Trek fans gathered and a tremendous time was had by practically everyone. But even while away and traveling, the science doesn’t stop, and I couldn’t help myself from sharing another dose of bonus science with you all.
Check out our comments of the week and enjoy!
Ask Ethan: Does Light Always Move At The Same Speed?
“Does light always move at the same speed? If it is slowed down by something, will is stay slower after it is no longer being slowed down? Will [it] speed back up to the speed of light?”
Throughout the entire Universe, there’s a fundamental law that governs the motions of all particles: Einstein’s relativity. It states that all particles with mass can never attain the speed of light, no matter how much energy you put into it. Additionally, all massless particles only move at the speed of light, no matter what you do to either them or to the device/person observing them. No matter what reference frame you’re in, the speed of light in a vacuum is a constant. But light isn’t always in a vacuum! From air to quartz to acrylic to glass to many other media, light can pass through transparent material, and when it does, it slows down. Not only that, but light of different energy slows down by different amounts. In what ways is the speed of light always the same, and in what ways can it change?
And most importantly, what do the known properties of light mean for the rest of the Universe? Find out on this edition of Ask Ethan!
Ask Ethan: Can The Universe Ever Expand Faster Than The Speed Of Light?
“In the first millionths of a second of the Big Bang did the universe not expand faster than the speed of light?”
You know it as the most fundamental law of relativity: that nothing can travel faster than the speed of light. And yet, the observable Universe itself, which has been around for 13.8 billion years since the Big Bang, is now 46.1 billion light years in radius. If everything were contracted down to a tiny volume of space, it seems that such a size would be impossible to achieve. Unless, somehow, space itself were expanding faster than the speed of light. As it turns out, though, not only is it still true that nothing can travel faster than light, but space itself doesn’t even expand at a speed at all! The reason for the confusion is that space expands at a speed-per-unit-distance, which allows the Universe to expand, light to redshift, and galaxies to appear to recede, all without exceeding the cosmic speed limit at all.
Want to finally wrap your head around the size and expansion of the Universe? Make sure you don’t miss your chance on this week’s Ask Ethan!
The Failed Experiment That Changed The World
This null result — the fact that there was no luminiferous aether — was actually a huge advance for modern science, as it meant that light must have been inherently different from all other waves that we knew of. The resolution came 18 years later, when Einstein’s theory of special relativity came along. And with it, we gained the recognition that the speed of light was a universal constant in all reference frames, that there was no absolute space or absolute time, and — finally — that light needed nothing more than space and time to travel through.
In the 1880s, it was clear that something was wrong with Newton’s formulation of the Universe. Gravitation didn’t explain everything, objects behaved bizarrely close to the speed of light, and light was exhibiting wave-like properties. But surely, even if it were a wave, it required a medium to travel through, just like all other waves? That was the standard thinking, and the genius of Albert A. Michelson was put to work to test it. Because, he reasoned, the Earth was moving around the Sun, the speed of light should get a boost in that forward direction, and then have to fight that boost on the return trip. The perpendicular direction, on the other hand, would be unaffected. This motion of light should be detectable in the form of interferometry, where light was split into two perpendicular components, sent on a journey, reflected, and then recombined.
The null results of this experiment changed the Universe, and the technology is still used today in experiments like LIGO. Come learn about the greatest failed experiment of all-time!