Sorry, Stephen Hawking, But Every Black Hole Is Still Growing, Not Decaying
“It remains true that every black hole that exists in the Universe should emit Hawking radiation, and that if you wait long enough, all of these black holes will eventually decay. But in our Universe so far, based on the black holes that actually exist, not a single black hole has even begun to decay in a meaningful way. The amount and energy of the radiation that’s out there, from starlight and left over from the Big Bang, ensures that black holes will absorb it and grow much more quickly than they lose energy from radiating it away.
Even though it’s been more than 45 years since Hawking first figured out that black holes do emit radiation, as well as what that radiation must look like, it’s far too faint and sparse for us to have ever detected it. Unless there’s a surprisingly low-mass black hole or we’re willing to wait an enormous, cosmic time for the Universe to cool, we’ll never be able to see it. Black holes are growing, not decays, and astrophysics teaches us exactly why.”
Yes, black holes emit radiation of exactly the type described by Stephen Hawking: a low-energy spectrum of photons and other particles arising from the physics of quantum field theory in curved spacetime. But, for much longer, we’ve known that black holes must also be absorbing energy over time, from matter, from starlight, and from the cosmic microwave background radiation.
The results are in, and every realistic black hole in the Universe is growing, not decaying, and it isn’t even close.
Ask Ethan: Can Black Holes Ever Spit Anything Back Out?
“Do black holes ever spit things out at any time? And if they do, do they ever spit out light?”
Sometimes, it’s the simplest-sounding questions that are the most profound. If you consider the name “black hole,” you’ll likely think that it doesn’t emit any type of light, and hence, it must be black. Only, if you look at a realistic black hole, it turns out it isn’t black at all. Black holes with material around them emit both jets and radiation; black holes in the presence of light will develop photon spheres and display that famous donut shape like the Event Horizon Telescope revealed earlier this year; even black holes in isolation will still emit Hawking radiation!
But can any of these types of radiation, varied and real though they may be, actually constitute something being spit back out of a black hole? Find out today!
The Science Of Why 5G Is (Almost) Certainly Safe For Humans
“Finally, the benefits that 5G will bring to society in the coming decade are truly revolutionary. In addition to the accelerated speeds that regular consumers will see, laying the infrastructure for 5G will enable civilization-changing smart technologies and a virtually unlimited number of device connections. 5G will enable blossoming technologies that rely on connectivity to the internet to go widespread, from connected self-driving cars to smart plugs, lights, cameras, toothbrushes, thermostats, healthcare monitoring devices and more. The Internet of Things is coming, and 5G is the technology that will take it mainstream.
There are lots of real hazards out there in the world, but 5G — much like vaccines, fluoridated drinking water, and the vapor trails left by airplanes — aren’t among them. In the search for truth, society should rely on the full suite of scientific evidence, rather than fear or ideology, to guide us. When we do, all of us can reap the benefits of a safe, connected world.”
Remember how big of a leap it was when we transitioned from 3G to 4G technologies? The jump from text and SMS messaging to streaming online video represented a factor of ~500 improvement in bandwidth, and the jump to 5G should not only give us an additional factor of 100, but should enable billions of additional connected devices. The Internet of Things is coming, and 5G is the technology that will bring it to fruition.
But is it safe for humans? Although there’s a lot of fearmongering and conspiracy theorizing surrounding it, there’s an awful lot of science, too. Here’s why it indicates that 5G is almost certainly safe for humans.
Cosmic Rays Are More Energetic Than LHC Particles, And This Faster-Than-Light Trick Reveals Them
“The other option would be to catch these cosmic ray particles before they ever reached the Earth; you’d need to go to space to see them. But even if you did that, you’d be limited by the sensitivity of your detector and the amount of energy that could be directly deposited within it. Going to space also comes with a tremendous launch cost; the Fermi gamma ray telescope, which detects individual high-energy photons rather than cosmic rays directly, cost approximately $690 million, more than twice the projected cost of the entire Čerenkov Telescope Array.
Instead, by catching the particles and photons that result from a cosmic ray striking the atmosphere in over 100 locations across the globe, we can come to understand the origin and properties of these ultra-relativistic particles, as well as the astrophysical sources that create them. All of this is possible because we understand the physics of particles moving faster-than-light in one special medium: Earth’s atmosphere. Einstein’s laws might be unbreakable, but the trick of slowing light down enables us to detect something very cleverly that we wouldn’t be able to measure otherwise!”
If you want to measure a high-energy particle, you build an enormous detector. You do this because you want the particle and its decay products (or secondary particles) to deposit their energy in the detector, so you can reconstruct their position, momenta, charge, and other properties that will enable you to understand where they came from. But the Universe gives us particles that are far too high in energy for that to be a workable solution. So what do we do, as physicists?
We use all the tricks nature makes available to us, including slowing light down to leverage the phenemenon of Cherenkov radiation! Here’s how we’re reconstructing cosmic rays from the ground with this special type of light.
Ask Ethan: Could The Energy Loss From Radiating Stars Explain Dark Energy?
“What happens to the gravity produced by the mass that is lost, when it’s converted by nuclear reactions in stars and goes out as light and neutrinos, or when mass accretes into a black hole, or when it’s converted into gravitational waves? […] In other words, are the gravitational waves and EM waves and neutrinos now a source of gravitation that exactly matches the prior mass that was converted, or not?”
For the first time in the history of Ask Ethan, I have a question from a Nobel Prize-winning scientist! John Mather, whose work on the Cosmic Microwave Background co-won him a Nobel Prize with George Smoot, sent me a theory claiming that when matter gets converted into radiation, it can generate an anti-gravitational force that might be responsible for what we presently call dark energy. It’s an interesting idea, but there are some compelling reasons why this shouldn’t work. We know how matter and radiation and dark energy all behave in the Universe, and converting one into another should have very straightforward consequences. When we take a close look at what they did, we can even figure out how the theory’s proponents fooled themselves.
Radiating stars and merging black holes do change how the Universe evolves, but not in a way that can mimic dark energy! Come find out how on this week’s Ask Ethan.
Ask Ethan: Can We Build A Sun Screen To Combat Global Climate Change?
“[W]hy don’t we evaluate building a “sun screen” in space to alter the amount of light (energy) earth receives? Everybody who did feel a total eclipse knows temperature goes down and light dims. So the idea is to build something that would stay between us and sun all year long…”
The Earth’s temperature is rising: that’s a fact. The overwhelming cause of this warming is human-caused emissions of greenhouse gases, like CO2 and methane. The CO2 concentration has now passed 410 parts per million, an increase of over 50% over pre-industrial revolution levels. If we cannot or will not reverse what’s driving the temperature change, we could instead try to counteract it. One proposal is to put a large device in space, between the Sun and the Earth, to block some of the incoming sunlight. As it turns out, blocking 2% would be enough to completely counteract the effects of human-caused global warming. Modifying our atmosphere is risky, but placing a sun screen in space to do the job has only one real drawback: its expense.
But how expensive is it, truly, when you consider the positive effects it would have on the planet? Let’s consider what it would take to combat global climate change by putting a shade in space!
How Does Our Earliest Picture Of The Universe Show Us Dark Matter?
“So all you need to do, to know whether your Universe has dark matter or not, is to measure these temperature fluctuations that appear in the CMB! The relative heights, locations, and numbers of the peaks that you see are caused by the relative abundances of dark matter, normal matter, and dark energy, as well as the expansion rate of the Universe. Quite importantly, if there is no dark matter, you only see half as many total peaks! When we compare the theoretical models with the observations, there’s an extremely compelling match to a Universe with dark matter, effectively ruling out a Universe without it.”
If your young Universe is full of matter and radiation, what happens? Gravitation works to pull matter into the overdense regions, but that means that the radiation pressure must rise in those regions, too, and that pushes back against the matter. On small scales, this pushback washes out the gravitational growth, but on large-enough scales, the finite speed that light can travel means that no wash-out can happen. Dark matter, however, doesn’t collide with radiation or normal matter, while normal matter collides with both radiation and itself. If we can calculate exactly how these three species interplay, we can calculate what types of patterns we expect to see in the Big Bang’s leftover glow, and then compare it with what we observe with satellites like WMAP and Planck. And what have we seen, exactly, when we’ve done that?
We see that the Universe must contain dark matter to explain the observations. No alternative theory can match it.