Dark energy: The apocalyptic wild card of the universe
Dr. Katie Mack explains what dark energy is and two ways it could one day destroy the universe.
KATIE MACK: Understanding what dark energy is, understanding what it is that's making the universe expand faster is an incredibly important thing for understanding the future of the universe. Right now, the evolution of the cosmos is dominated by this mysterious dark energy that we can't see, we don't understand. If we figure out what it's doing, if we figure out what it's made of, how it's going to change in the future, then we will have a much better idea for how the universe will end.
Dark matter is very different from dark energy. People often get these two ideas confused because they're both called dark. And also because there are connections between matter and energy. People might have heard of E = mc2, this idea that there's a way to relate the mass of something to its energy, that's from Einstein. In this case, dark matter and dark energy don't seem to be related to each other in any way, that we know. They're both called dark because we cannot see them and they're mysterious. That's where the similarity ends. Neither one is dark in the sense of being black. They're dark in the sense of being invisible. They don't emit light, they don't absorb light, they don't reflect light. They don't seem to interact with light at all, as far as we can tell.
Dark matter seems to be something that interacts via gravity so it has mass, it's matter. But it doesn't seem to interact via the other forces of nature in any way that we've been able to tell. Dark energy only does this thing where it makes space expand, it interacts only with space. And there's a possibility that dark energy is just a property of space that every little bit of space has a little bit of expansion built in, and as the universe gets bigger and bigger, there's more and more space, and so that expansion starts to win out over the gravity that's trying to slow it down. And so, the universe starts expanding faster and faster. That's one possibility for dark energy, that it's just a cosmological constant, it's just part of how the universe works, that it has this expansiveness built into it.
But it's possible it's something else. It's possible that whatever is making the universe expand faster and faster is something weird and different, something that acts in a totally different way. That also accelerates the expansion of the universe, but maybe it changes over time in some way that we don't understand. One of the possibilities for that is something called phantom dark energy. Phantom dark energy would be something where dark energy is getting more powerful over time. That means that in a particular volume of space, the amount of dark energy in that volume starts growing. And that would actually lead to a total apocalypse in a relatively short time. What it would do is it would start tearing apart things in the universe. If dark energy is not a cosmological constant, if it's this phantom dark energy, then the amount of dark energy is going to get higher over time. And so, the stars that have been orbiting very stably in the past will start to feel pushed out by more and more of this expansion happening inside the galaxy.
So, in the scenario that dark energy is this weird stuff, this phantom dark energy, then it does start to actually pull matter apart. So it would first start to pull galaxies away from other galaxies in these giant galaxy clusters. Then it would start to pull stars away from galaxies, so we'd see the stars in the Milky Way would start to drift away. And then it would start to pull planets away from their suns. And then, it would start to actually pull apart planets and stars, and even eventually atoms and particles—it would start to just rip everything apart. And in some, at some point in the future, it would kinda tear apart the whole universe in a process we know as The Big Rip.
So, based on our current data, there's some uncertainty in our current measurements of the expansion of the universe. And that uncertainly leaves some space for the possibility that our universe is headed toward a Big Rip. And based on the uncertainties in the measurements, what we can say is that we're almost certain not to have a Big Rip in the next 200 billion years or so. But we can't say for sure that it will never happen. And even as we get more and more precise measurements, all that's really going to do is push this scenario farther into the future, and say, well, maybe we'll get much better measurements in a few years, and then that'll tell us we definitely won't have a Big Rip for the next hundred thousand billion years. You might, at some point, get to that, but you'll never be able to say that it'll never happen because no measurement is ever 100% complete. So unless we really understand what dark energy is, which at the moment, we don't, we can't say for certain that it won't at some point, rip the universe apart. We can just say that if it's going to do that, it'll be a really long time from now.
Alternatively, dark energy could be something that changes fundamentally over time, that doesn't get more powerful, but gets less powerful and actually changes direction. So, dark energy could be something that's currently making the universe expand faster, but it could be something that changes and at at some point, starts to pull the universe back together again. Right now, we know that the universe is expanding, galaxies are getting farther apart from each other. And for a long time, we were trying to measure how quickly that expansion was slowing down. And we figured it should be slowing down because the Big Bang happened in the beginning, that kicked off the expansion, and since then, all the gravity of all the stuff in the universe should be kinda putting on the brakes, kinda pulling things back.
For a long time, we didn't know if the gravity would eventually win, or if the expansion was so powerful that everything will be moving away from everything else forever. And if the gravity were to win, then what would happen is the expansion, at some point, would stop. And distant galaxies, instead of moving away from us, would start barreling toward us in the future. And the way that it would look to us is that we would see distant galaxies kinda coming toward us. We would see collisions of galaxies much more often. Other galaxies would collide with our galaxy. There would be a lot more stuff in the smaller region of space, just everywhere in the universe. The universe would get much more dense.
And the thing that would actually get dangerous about that, the first thing that would get dangerous about that is that as the universe is compressing, it's not just compressing like the galaxies, the stars, and stuff like that, it's compressing all of the radiation in the universe as well. And we know that there's background radiation in our universe today that's leftover from the time when the early universe was very hot and dense. It dissipated. It sort of spread out, but that radiation is still out there. And so, if you're compressing the universe, you're bringing all that radiation back into a smaller space. And so, you're moving toward being back in that plasma state, you're evolving toward being, the whole universe being hot and dense, and in sort of this roiling plasma. As the universe is compressing, not only is it bringing back all that radiation from the primordial fire, it's also compressing all the radiation from all of the stars that ever burned in the universe.
More and more, any random point in the universe would feel a lot more like being right next to a star. And all of these high energy processes in the universe that create gamma rays and x-rays, that radiation also would be compressed. And so, at some point, as you're evolving toward a Big Crunch scenario, as the universe is compressing, you get to a point when there's so much radiation in the universe, just an empty space, just so much radiation that it's enough to ignite the surfaces of stars. And what I mean by that is that there's so much of this high energy radiation just flowing through the universe, that the outsides of stars start carrying out thermonuclear explosions. So stars will start to just burn from the outside in. And at that point, you know, it's all over. Nothing can survive conditions like that. And you end up with just total destruction. That's The Big Crunch. The only way we can see that happening is if dark energy is so weird that it doesn't just cause expansion, it actually stops, turns around, and causes compression. And because we don't know what dark energy is, we don't know if it's something that can change over time. We don't know if it's on some trajectory. We can't rule out the idea that it could, at some point, reverse directions. We think that's probably not going to happen.
- The universe is expanding faster and faster. Whether this acceleration will end in a Big Rip or will reverse and contract into a Big Crunch is not yet understood, and neither is the invisible force causing that expansion: dark energy.
- Physicist Dr. Katie Mack explains the difference between dark matter, dark energy, and phantom dark energy, and shares what scientists think the mysterious force is, its effect on space, and how, billions of years from now, it could cause peak cosmic destruction.
- The Big Rip seems more probable than a Big Crunch at this point in time, but scientists still have much to learn before they can determine the ultimate fate of the universe. "If we figure out what [dark energy is] doing, if we figure out what it's made of, how it's going to change in the future, then we will have a much better idea for how the universe will end," says Mack.
- Heat death: How will the universe end? - Big Think ›
- Dark Matter and Dark Energy Don't Exist. New Theory Says the ... ›
- Mystery effect speeds up the Universe – not dark energy, says study ... ›
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Scientists are using bioelectronic medicine to treat inflammatory diseases, an approach that capitalizes on the ancient "hardwiring" of the nervous system.
- Bioelectronic medicine is an emerging field that focuses on manipulating the nervous system to treat diseases.
- Clinical studies show that using electronic devices to stimulate the vagus nerve is effective at treating inflammatory diseases like rheumatoid arthritis.
- Although it's not yet approved by the US Food and Drug Administration, vagus nerve stimulation may also prove effective at treating other diseases like cancer, diabetes and depression.
The nervous system’s ancient reflexes<p>You accidentally place your hand on a hot stove. Almost instantaneously, your hand withdraws.</p><p>What triggered your hand to move? The answer is <em>not</em> that you consciously decided the stove was hot and you should move your hand. Rather, it was a reflex: Skin receptors on your hand sent nerve impulses to the spinal cord, which ultimately sent back motor neurons that caused your hand to move away. This all occurred before your "conscious brain" realized what happened.</p><p>Similarly, the nervous system has reflexes that protect individual cells in the body.</p><p>"The nervous system evolved because we need to respond to stimuli in the environment," said Dr. Tracey. "Neural signals don't come from the brain down first. Instead, when something happens in the environment, our peripheral nervous system senses it and sends a signal to the central nervous system, which comprises the brain and spinal cord. And then the nervous system responds to correct the problem."</p><p>So, what if scientists could "hack" into the nervous system, manipulating the electrical activity in the nervous system to control molecular processes and produce desirable outcomes? That's the chief goal of bioelectronic medicine.</p><p>"There are billions of neurons in the body that interact with almost every cell in the body, and at each of those nerve endings, molecular signals control molecular mechanisms that can be defined and mapped, and potentially put under control," Dr. Tracey said in a <a href="https://www.youtube.com/watch?v=AJH9KsMKi5M" target="_blank">TED Talk</a>.</p><p>"Many of these mechanisms are also involved in important diseases, like cancer, Alzheimer's, diabetes, hypertension and shock. It's very plausible that finding neural signals to control those mechanisms will hold promises for devices replacing some of today's medication for those diseases."</p><p>How can scientists hack the nervous system? For years, researchers in the field of bioelectronic medicine have zeroed in on the longest cranial nerve in the body: the vagus nerve.</p>
The vagus nerve<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNTYyOTM5OC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY0NTIwNzk0NX0.UCy-3UNpomb3DQZMhyOw_SQG4ThwACXW_rMnc9mLAe8/img.jpg?width=1245&coordinates=0%2C0%2C0%2C0&height=700" id="09add" class="rm-shortcode" data-rm-shortcode-id="f38dbfbbfe470ad85a3b023dd5083557" data-rm-shortcode-name="rebelmouse-image" data-width="1245" data-height="700" />
Electrical signals, seen here in a synapse, travel along the vagus nerve to trigger an inflammatory response.
Credit: Adobe Stock via solvod<p>The vagus nerve ("vagus" meaning "wandering" in Latin) comprises two nerve branches that stretch from the brainstem down to the chest and abdomen, where nerve fibers connect to organs. Electrical signals constantly travel up and down the vagus nerve, facilitating communication between the brain and other parts of the body.</p><p>One aspect of this back-and-forth communication is inflammation. When the immune system detects injury or attack, it automatically triggers an inflammatory response, which helps heal injuries and fend off invaders. But when not deployed properly, inflammation can become excessive, exacerbating the original problem and potentially contributing to diseases.</p><p>In 2002, Dr. Tracey and his colleagues discovered that the nervous system plays a key role in monitoring and modifying inflammation. This occurs through a process called the <a href="https://www.nature.com/articles/nature01321" target="_blank" rel="noopener noreferrer">inflammatory reflex</a>. In simple terms, it works like this: When the nervous system detects inflammatory stimuli, it reflexively (and subconsciously) deploys electrical signals through the vagus nerve that trigger anti-inflammatory molecular processes.</p><p>In rodent experiments, Dr. Tracey and his colleagues observed that electrical signals traveling through the vagus nerve control TNF, a protein that, in excess, causes inflammation. These electrical signals travel through the vagus nerve to the spleen. There, electrical signals are converted to chemical signals, triggering a molecular process that ultimately makes TNF, which exacerbates conditions like rheumatoid arthritis.</p><p>The incredible chain reaction of the inflammatory reflex was observed by Dr. Tracey and his colleagues in greater detail through rodent experiments. When inflammatory stimuli are detected, the nervous system sends electrical signals that travel through the vagus nerve to the spleen. There, the electrical signals are converted to chemical signals, which trigger the spleen to create a white blood cell called a T cell, which then creates a neurotransmitter called acetylcholine. The acetylcholine interacts with macrophages, which are a specific type of white blood cell that creates TNF, a protein that, in excess, causes inflammation. At that point, the acetylcholine triggers the macrophages to stop overproducing TNF – or inflammation.</p><p>Experiments showed that when a specific part of the body is inflamed, specific fibers within the vagus nerve start firing. Dr. Tracey and his colleagues were able to map these relationships. More importantly, they were able to stimulate specific parts of the vagus nerve to "shut off" inflammation.</p><p>What's more, clinical trials show that vagus nerve stimulation not only "shuts off" inflammation, but also triggers the production of cells that promote healing.</p><p>"In animal experiments, we understand how this works," Dr. Tracey said. "And now we have clinical trials showing that the human response is what's predicted by the lab experiments. Many scientific thresholds have been crossed in the clinic and the lab. We're literally at the point of regulatory steps and stages, and then marketing and distribution before this idea takes off."<br></p>
The future of bioelectronic medicine<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNTYxMDYxMy9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYzNjQwOTExNH0.uBY1TnEs_kv9Dal7zmA_i9L7T0wnIuf9gGtdRXcNNxo/img.jpg?width=980" id="8b5b2" class="rm-shortcode" data-rm-shortcode-id="c005e615e5f23c2817483862354d2cc4" data-rm-shortcode-name="rebelmouse-image" data-width="2000" data-height="1125" />
Vagus nerve stimulation can already treat Crohn's disease and other inflammatory diseases. In the future, it may also be used to treat cancer, diabetes, and depression.
Credit: Adobe Stock via Maridav<p>Vagus nerve stimulation is currently awaiting approval by the US Food and Drug Administration, but so far, it's proven safe and effective in clinical trials on humans. Dr. Tracey said vagus nerve stimulation could become a common treatment for a wide range of diseases, including cancer, Alzheimer's, diabetes, hypertension, shock, depression and diabetes.</p><p>"To the extent that inflammation is the problem in the disease, then stopping inflammation or suppressing the inflammation with vagus nerve stimulation or bioelectronic approaches will be beneficial and therapeutic," he said.</p><p>Receiving vagus nerve stimulation would require having an electronic device, about the size of lima bean, surgically implanted in your neck during a 30-minute procedure. A couple of weeks later, you'd visit, say, your rheumatologist, who would activate the device and determine the right dosage. The stimulation would take a few minutes each day, and it'd likely be unnoticeable.</p><p>But the most revolutionary aspect of bioelectronic medicine, according to Dr. Tracey, is that approaches like vagus nerve stimulation wouldn't come with harmful and potentially deadly side effects, as many pharmaceutical drugs currently do.</p><p>"A device on a nerve is not going to have systemic side effects on the body like taking a steroid does," Dr. Tracey said. "It's a powerful concept that, frankly, scientists are quite accepting of—it's actually quite amazing. But the idea of adopting this into practice is going to take another 10 or 20 years, because it's hard for physicians, who've spent their lives writing prescriptions for pills or injections, that a computer chip can replace the drug."</p><p>But patients could also play a role in advancing bioelectronic medicine.</p><p>"There's a huge demand in this patient cohort for something better than they're taking now," Dr. Tracey said. "Patients don't want to take a drug with a black-box warning, costs $100,000 a year and works half the time."</p><p>Michael Dowling, president and CEO of Northwell Health, elaborated:</p><p>"Why would patients pursue a drug regimen when they could opt for a few electronic pulses? Is it possible that treatments like this, pulses through electronic devices, could replace some drugs in the coming years as preferred treatments? Tracey believes it is, and that is perhaps why the pharmaceutical industry closely follows his work."</p><p>Over the long term, bioelectronic approaches are unlikely to completely replace pharmaceutical drugs, but they could replace many, or at least be used as supplemental treatments.</p><p>Dr. Tracey is optimistic about the future of the field.</p><p>"It's going to spawn a huge new industry that will rival the pharmaceutical industry in the next 50 years," he said. "This is no longer just a startup industry. [...] It's going to be very interesting to see the explosive growth that's going to occur."</p>
"The Expanse" is the best vision I've ever seen of a space-faring future that may be just a few generations away.
- Want three reasons why that headline is justified? Characters and acting, universe building, and science.
- For those who don't know, "The Expanse" is a series that's run on SyFy and Amazon Prime set about 200 years in the future in a mostly settled solar system with three waring factions: Earth, Mars, and Belters.
- No other show I know of manages to use real science so adeptly in the service of its story and its grand universe building.
Credit: "The Expanse" / Syfy<p>Now, I get it if you don't agree with me. I love "Star Trek" and I thought "Battlestar Galactica" (the new one) was amazing and I do adore "The Mandalorian". They are all fun and important and worth watching and thinking about. And maybe you love them more than anything else. But when you sum up the acting, the universe building, and the use of real science where it matters, I think nothing can beat "The Expanse". And with a <a href="https://www.rottentomatoes.com/tv/the_expanse" target="_blank">Rotten Tomato</a> average rating of 93%, I'm clearly not the only one who feels this way.</p><p>Best.</p><p>Show.</p><p>Ever. </p>
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