Relativity Wasn’t Einstein’s Miracle; It Was Waiting In Plain Sight For 71 Years
“If the Universe had a frame of reference that was distinct from all the others, then there should be some measurement you could make that revealed to you how the laws of nature were different when you moved at one particular speed in one particular direction. But that is inconsistent with the Universe we have. No matter how fast you move or what direction you move in, the laws of physics are the same, and any physical experiment you can perform will give the same measurable results and result in the same physical phenomena.”
When we think about Einstein and the principle of relativity, we normally talk about the Michelson-Morley experiment, which showed that the speed of light remained constant whether it was aligned with or at an angle to Earth’s motion. We might think about the Lorentz transformations like time dilation or length contraction. Certainly, those results played a role, but Einstein himself was thinking about a puzzle that came to light much earlier: about what’s physically occurring to cause Faraday’s law of induction. If you move a bar magnet into a stationary coil of wire, you generate an electric current. If you move a coil of wire onto or off of a stationary bar magnet, you also generate an equal intensity electric current. But the physics of how is entirely different!
Ask Ethan: How Can We Measure The Curvature Of Spacetime?
“The Universe is not simply made of point masses, but of complex, intricate objects. If we ever hope to tease out the most sensitive signals of all and learn the details that elude us today, we need to become more precise than ever. Thanks to three-atom interferometry, we can, for the first time, directly measure the curvature of space.
Understanding the Earth’s interior better than ever is the first thing we’re going to gain, but that’s just the beginning. Scientific discovery isn’t the end of the game; it’s the starting point for new applications and novel technologies. Come back in a few years; you might be surprised at what becomes possible based on what we’re learning for the first time today.”
Go out and measure how an object falls: that gives you gravitational acceleration. Go out and measure how that falling is different between two locations identical in every way except at different elevations, and you’ll measure a gravitational gradient, sufficient for telling Einstein’s theory apart from Newton’s. But if you can measure the differences in gravitational acceleration between three locations at once, you can measure changes in that gradient, and come away with an understanding of spacetime curvature.
Ask Ethan: How Do Massless Particles Experience Gravity?
“Given the equation for gravity between two masses, and the fact that photons are massless, how is it possible for a mass (like a star or a black hole) to exert influence on said photon?”
You know the law of universal gravitation: you put in what any two masses are, how far apart they are from each other, and the gravitational constant of the Universe, and you can immediately know what the force is between any two objects. Set one of the masses to zero, and the force goes to zero. So why is it, then, that if you take the ultimate particle with no mass, a photon, and pass it close by a mass, its path does bend? Why do massless particles experience gravity?
To understand why, you should think about what happens if you and I start at the same place near a mass, but I’m stationary and you’re moving. How far away is that mass? What’s the “r” that goes into Newton’s equation? And who’s right: me or you?
Physicists Used Einstein’s Relativity To Successfully Predict A Supernova Explosion
“When the lens and a background source align in a particular fashion, quadruple images will result. With slightly different light-travel paths, the brightness and arrival time of each image is unique. In November 2014, a quadruply-lensed supernova was observed, showcasing exactly this type of alignment. Although a single galaxy caused the quadruple image, that galaxy was part of a huge galaxy cluster, exhibiting its own strong lensing effects. Elsewhere in the cluster, two additional images of the same galaxy also appear.”
We normally think of light traveling in a straight line, but that’s only true if your space is flat. In the real Universe, mass and matter not only exist, but clump together into massive structures like galaxies, quasars, and galaxy clusters. When a background source of light passes through these foreground masses, the light can get bent and distorted into multiple images that are magnified and arrive at slightly different times. If an event occurs in one such image, we can predict, based on General Relativity, cluster dynamics, and dark matter, when that event will appear in the other images.
“I’d like somebody to finally acknowledge and admit that showing balls on a bed sheet doesn’t cut it as a picture of reality.”
Okay, I admit it: visualizing General Relativity as balls on a bedsheet doesn’t make a whole lot of sense. For one, if this is what gravity is supposed to be, what pulls the balls “down” onto the bedsheet? For another, if space is three dimensional, why are we talking about a 2D “fabric” of space? And for another, why do these lines curve away from the mass, rather than towards it?
It’s true: this visualization of General Relativity is highly flawed. But, believe it or not, all visualizations of General Relativity inherently have similar flaws. The reason is that space itself is not an observable thing! In Einstein’s theory, General Relativity provides the link between the matter and energy in the Universe, which determines the geometric curvature of spacetime, and how the rest of the matter and energy in the Universe moves in response to that. In this Universe, we can only measure matter and energy, not space itself. We can visualize it how we like, but all visualizations are inherently flawed.
“Every time you see a diagram, an article, or a story talking about the “big bang singularity” or any sort of big bang/singularity existing before inflation, know that you’re dealing with an outdated method of thinking. The idea of a Big Bang singularity went out the window as soon as we realized we had a different state — that of cosmic inflation — preceding and setting up the early, hot-and-dense state of the Big Bang. There may have been a singularity at the very beginning of space and time, with inflation arising after that, but there’s no guarantee. In science, there are the things we can test, measure, predict, and confirm or refute, like an inflationary state giving rise to a hot Big Bang. Everything else? It’s nothing more than speculation.”
The Universe, as we observe it today, is expanding and cooling, with the overall density dropping as the volume of space increases. If we ran the clock backwards, however, instead of forwards, things would appear to contract, become denser, and grow hotter. If you go back farther and farther in time, you’d come to an epoch before there were stars and galaxies; before neutral atoms could stably form; before atomic nuclei could remain; etc. You’d go all the way back to hotter and denser states, eventually compressing all the matter and energy in the Universe into a single point: a singularity. This was the ultimate beginning of everything according to the original Big Bang: the birth of time and space.