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#751: Vacuum Energy

Astronomy Cast - Tue, 04/15/2025 - 6:00pm

Even empty space isn’t empty. It’s filled with the quantum fluctuations of spacetime itself. Which can be measured with famous experiments like the Casimir Effect. There is a surprising amount of energy in space itself, which has led to some interesting theories about how the future of the Universe might evolve. You can’t get something from nothing but sometimes that nothing is something you can get something from.

Show Notes

Universe as Wave Functions
Quantum Uncertainty
Heisenberg Uncertainty Principle
Zero-Point Energy
Casimir Effect Experiment
Vacuum Energy
Zero-Point Energy
Vacuum Energy Discrepancy
Potential Consequences of Vacuum Energy
Vacuum Energy and Space Expansion
Hawking Radiation & Unruh Effect
Inflation and Energy Levels
Vacuum Decay and Its Potential Consequences
Unknown Physics
Multiverse Collision
Speed of Collision Impact
Understanding the Universe
Potential Risks
Black Hole Evaporation
Cosmic Ray Energy
Future Particle Accelerators

Transcript

Fraser Cain: It’s the 365 Days of Astronomy podcast, coming in three, two, one. ♪♪ ♪♪ AstronomyCast, Episode 751, Vacuum Energy. Welcome to AstronomyCast, our weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know.

I’m Fraser Cain, I’m the publisher of Universe Today. With me as always is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute, and the director of CosmoQuest. Hey Pamela, how are you doing?

Dr. Pamela Gay: I am doing well. We have hit one of the key points in Spring. I know that once the apple tree is done blooming, it is safe to plant things into the ground.

And this weekend, the apple tree decided it would bloom.

Fraser Cain: I have completely unrelated news that has nothing to do with Spring, and that is, thank you everybody who responded so incredibly to my desperate plea for a new business model a couple of weeks ago. People were amazing, and generous, and kind, and we did it. That we completely filled the Universe Today gap in the business model.

That removing ads from the website was exactly the right move. And I now live in this post-algorithm, SEO, AI slop, business model, ad network vision of the future, where I just think about the stories that we want to cover, and then we just do it, and then that’s that. It’s amazing.

Dr. Pamela Gay: That’s amazing. I am so happy for you.

Fraser Cain: Yeah, yeah. It’s absolutely incredible. Just to, and you don’t realize, I know I’m going to take another, I don’t know, year to decompress, because so much, the last 26 years of my life has been, well, what will the search engines think?

What does the algorithm want? What am I supposed to do? What do I do now?

And now, I don’t even look at my website traffic. I don’t even think about anything. I’m curious about a story, one of the writers works on that story, and then I am curious about a different story, and that’s it.

And so, we’ve been producing a ton of content, my brain is free and clear, and I’m really grateful to everybody who helped out. So if you are one of those people, thank you so much. You saved my business.

Even an empty space isn’t empty. It’s filled with the quantum fluctuations of space-time itself, which can be measured with famous experiments like the Casimir effect. There is a surprising amount of energy in space itself, which has led to some interesting theories about how the future of the Universe might evolve.

All right, Pamela, so I think we all imagine the Universe as a bunch of little particles flying around or clustered together. We imagine photons zipping through the Universe, but that’s not how a particle physicist truly thinks about the nature of the Universe.

Dr. Pamela Gay: Now, the wave-particle duality of nature is one of the weirder things that we learn about in physics, and it turns out that when you want to think about the Universe, you want to think about it as a number of wave functions that are all interacting with each other. And when we have particles, when we have atoms, what we have is something that has a wavelength, that has a frequency, and it has an energy, and there is a zero-point energy to everything that defines the lowest quantized energy that is possible. And even the Universe, we think, is quantized in its very nature.

Fraser Cain: Whoa. So, again, I’m imagining this proton of hydrogen flying along in the Universe, and it’s not actually a proton of hydrogen. It is a combined wave function across the entire Universe, with a probability of it being the proton that I’m imagining, but also a probability of it being somewhere else as well.

Dr. Pamela Gay: Yeah. Yeah. That’s the messed-up thing.

In general, when you run the equations, things have a kind of mostly known position. Even the Heisenberg Uncertainty Principle, which we did an entire show on ages and ages ago, basically says you can either know mostly where something is or mostly how fast it is. You can’t know both at the same time.

Pick what you want to be accurate about. And so we can get roughly at something’s location. We can get roughly at something’s velocity.

And we can totally get at its energy, we think. And it’s this compilation of energies that builds up to describe our Universe.

Fraser Cain: Right. Okay. And so when you’re talking about that idea of zero-point energy, are you saying that there is this theoretical bottom point, and then you could take your photon and then you could measure its probability across the entire Universe and you’re going to get probability numbers and they can never go down to that zero, which means that although the photon is most likely here in the room with us today, it could be anywhere.

Dr. Pamela Gay: Is that right? It even gets more specific than that. So one of the coolest things is you can take a container and you can imagine that you have attempted to remove all of the mass from it, but because it’s in our Universe, it’s going to have energy in it.

And the zero-point energy of that cavity is defined by the sum of all particles that are capable of existing within that size of a cavity. And so…

Fraser Cain: Nobody ordered this.

Dr. Pamela Gay: This starts to get us to craziness where if you take… and there is an out for what I’m about to say. There is an out.

If you take all the known particles and the size of the Universe, you get to an infinite background energy, which is not something… infinities don’t exist, we don’t believe. They’re just math.

So we have to start looking at things purely in terms of the differences in energy. So you can start to calculate what is the difference in energy between two different containers, one with inside of another one. And this kind of a thought experiment led to actual experiments looking at things like the Casimir effect.

Fraser Cain: Yeah. And this is one of the most mind-bending experiments that’s ever been done, which is like proof positive that this thing that sounds too weird to be true is really true. So can you just explain this?

Dr. Pamela Gay: All right. So imagine that you have two sets of parallel plates. We’re just going to make it as easy as possible.

Energy is inversely proportional to wavelength. So things that have little tiny wavelengths have really big energies. X-ray light, short wavelength, infrared light, long wavelength.

X-ray is going to blast your DNA, IR is just going to warm you up. So you have these two different sets of plates. And you look at what are the wavelengths that fit between the large ones, what are the wavelengths that fit between the small ones.

And you have tiny wavelengths between the small ones. Now, if you decrease the distance between the two closest plates, you have now increased the energy between these two plates. And this ends up causing a bulk force that affects the separation of the plates.

Now, exactly what happens depends on the geometry of a system. You have to be able to get things super close together in order for you to be able to start to see things like this. But folks working with thin films have been able to measure within 5% of what was theoretically predicted the value of the Casimir effect between thin films.

Fraser Cain: And so you get these, only the smallest wavelength fluctuations can fit within the plates. And so you’ve got the small wavelengths, high energy in between the plates, you’ve got the large wavelength. And what you get is a force pushing the plates together.

And literally you just, if you put two plates close together, they’re going to want to push together closer with more force because of this detectable phenomenon. It is, it is bonkers. And it is this like one of the best pieces of evidence that shows that this is real.

So is this vacuum energy, quantum energy, like help me understand what is the distinction between those different concepts?

Dr. Pamela Gay: So vacuum energy is the energy that’s just kind of everywhere. And it can vary. So the amount of vacuum energy you have between those two thin plates and the amount of vacuum energy you have in a room like the one we’re sitting in are two different values.

But overall, the universe has a zero point energy that nothing can get below.

Fraser Cain: Right.

Dr. Pamela Gay: And this can be gotten at, again, the math doesn’t match what we see, can get, you can get at it by adding up what are all the possible particle combinations that could exist, looking at all the different non particles. And then we have to remember, we don’t actually understand how to quantify gravity. And so a whole lot of work has been done to try and say, okay, so this background energy that is absolutely everywhere that we see fluctuations, like you stick mass somewhere, that’s a bunch of energy.

Clearly, you don’t have zero point energy on a planet. But when you start to figure out could this zero point energy, could this background energy be what’s powering dark energy? And this was like the first place people went when they were trying to understand what dark energy is.

You end up with a difference of a factor of 10 to the 140 last time I looked up the numbers. And that’s kind of an obscene difference. And the only way we have to justify this extreme difference is, well, we haven’t included gravity yet, which is kind of uncomfortable, but that’s where we are, folks.

But at the same time, zero point energy has some super weird and extremely troubling potential consequences.

Fraser Cain: Yeah. So, so I just want to sort of go back to what you just mentioned. So, in other words, it’s not surprising or it’s not completely unsurprising that when you have more space, then you have more vacuum energy because you have more space, more place to put your quantum particles and your waves.

But also then you, that could then be, have being a force. We talked about the Casimir effect. So you could then imagine you get more space, you get more force, you get more, that creates more space, you get more force, and it just continues to add this pressure into the, into the universe.

But what you’re saying is, is that that’s great in theory, but the, but the amount that would be measurable is dramatically different than what we find. Yeah. Okay.

So then what are some of the sort of unsettling possibilities about this vacuum energy?

Dr. Pamela Gay: Okay. So we’re going to start with the least unsettling and perhaps the one that everyone is most familiar with. And that is black holes aren’t permanent.

If Hawking was correct. And here the idea is that the energy that you have just hanging out in space, being energy allows particles to zip in and out of existence. These are virtual particles, again, Casimir effect, we know they should exist.

Well, if, if space has all the quantities of a particle, if it has polarization, spin, all of these things, and we believe it does, this means you can have a matter particle and anti-matter particles spring into existence. And if they spring into existence and they both have mass and mass is just a quantity, it’s scalar. If they spring into existence on either side of the event horizon of a black hole, one of them can zip away while the other is trapped inside.

And the one that zips away, whether it’s matter or anti-matter, it’s carrying away mass.

Fraser Cain: So I’m going to do something completely unprecedented here in the show. And that I’m going to tell you that what you were describing is wrong. And that this is what Stephen Hawking put in his book, um, a short history of nearly everything.

And he knew that it was a misnomer and, and this sort of thought experiment has been debunked many times.

Dr. Pamela Gay: I read his book. I am guilty.

Fraser Cain: I know. I know. I know.

I know. And so let me take another crack at it, which is, and then we can sort of get to a more hybridized explanation. So, um, and I’m sorry to do this, but I know we’re going to get emails.

Dr. Pamela Gay: I am happy.

Fraser Cain: No, no. So, so, um, observational astronomer, I trust the books I read. So we know that when we, so there is this sort of mechanism called unruh radiation, and this is caused by an acceleration through the universe.

That if you were on a spacecraft and you were accelerating through the universe, you would be experiencing a flux of these particles of these virtual particles of these quantum waves striking your spacecraft. And it only exists when you are accelerated. And it’s like an increased amount of radiation that you’d be experiencing that is just coming from your interaction with space time itself.

And so we know that thanks to Einstein, your acceleration through the cosmos is equivalent to your being in a, in a gravity well, be it around a planet being around a black hole that if you closed your eyes and you couldn’t tell whether your spacecraft was accelerating through the universe and experiencing this bath of radiation, or whether you were under the influence of a really powerful gravity well that is then causing you to experience this radiation.

And so from the perspective of an outside observer, you will see radiation coming from both accelerating through the cosmos and being in the presence of a large black hole. Now this can’t come from nowhere. And so something has to give up the, has to give up the mass equivalent to the energy that is being radiated away by gravity wells, by objects, by mass.

And so that the thing that we experience is this, this Hawking radiation. And so it’s purely based on the equivalence principle between acceleration through space time and the being in a gravity well next to space time. And the amount of radiation you experience depends on the sharpness.

But it’s been theorized that even planets, people will Hawking radiate over long enough periods of time.

Dr. Pamela Gay: He lied to us with his analogy.

Fraser Cain: He admitted later that it was a rough analogy that wasn’t that useful. So yeah, yeah, yeah, I know. I know.

And so you’re hearing this all the time. And so now you get the comet brigade going, no, no, no, that’s not, that’s not true. And so, and so this, this idea of this unruh radiation is a, is sort of a much easier way to kind of wrap your mind around it.

And that gets away from the people asking like, oh, I thought that, um, you know, why is it if particles are going into the black hole, why does the black hole get less massive? Shouldn’t the black hole get more massive? Well, you know, the whole point is that, that it’s not about virtual particles that are going into black holes.

It is just about this equivalent that there is this effect on space time by both acceleration and mass because they’re equivalent.

Dr. Pamela Gay: So the wild thing is that I now need to figure out how to wrap my head around is black holes above a certain size aren’t actively getting smaller because of the amount of cosmic microwave background and other particles falling into them. So you don’t have to worry about massive black holes going away as long as we have things like the cosmic microwave background.

Fraser Cain: And because there’s still an influx of radiation coming from the CMB from particles dropping into them, whatever. And that you, you get the, the, the most of this evaporation, this radiation comes from the places where the gravity well is the steepest. And so that’s why the supermassive black holes radiate more slowly than actually the stellar mass black holes.

And the small primordial black holes will radiate the fastest. Right. They’ll go away because they have a really sharp, uh, like essentially a, a kink in their gravity.

Well, a point, a jerk, a moment of the highest acceleration.

Dr. Pamela Gay: Okay. So with that divergence aside, all right, with that divergence aside, let’s continue. Okay.

So now we can get to the extremely disturbing things. Yeah. So, so one of the ways that theorists have come up with to explain the period, the epic of inflation in the first moments of the universe where the universe went from atoms sized to solar system sized in a fraction of a moment, um, is that the universe was actually collapsing from one energy level to another and that energy expanded out our universe.

Now that implies that if we aren’t actually at a zero point energy, that we are, if we are at a quantized higher level, that the universe can again drop energy levels, right?

Fraser Cain: So what we think is the lowest amount of energy might not actually be the lowest amount of energy. Yikes.

Dr. Pamela Gay: And if we can drop energy levels again, that means we can go through inflation again. Yeah.

Fraser Cain: So like what you’re saying is like, you would like, we all, everything is nice and everything is balanced. I’m trying to, I’m trying to think of analogies, right? And so I’m sort of thinking about, let’s say an earth, you know, plate tectonics, you’ve got a bunch of plates that are sitting and they’ve reached this perfect equilibrium.

And then suddenly everything slips and shifts and you now move to a new equilibrium. But in between you had brutal earthquakes.

Dr. Pamela Gay: And it’s a little bit worse than that because, Oh great.

Fraser Cain: Yeah, no. What could be worse than brutal earthquakes?

Dr. Pamela Gay: Bring it on. So, if you think about it, we often talk about how trillions of years from now, everything will be a particle fog, essentially an energy fog. And on the way to that state, our galaxy will fall into a galaxy cluster.

Everything will slowly merge, but then everything beyond that cluster that we’re in will disappear over the horizon and we just won’t be able to get light from anything else because it’s too far away. Well, if we go through another inflation, we could have that happen fairly instantaneously at a random moment in time. And who knows what that will actually do to everything embedded in space-time.

Fraser Cain: Right. When you think about like the original inflation, it was something like everything in one, 10 to the power of minus 22 seconds, I don’t know what that is, a octotillionth of a second. The universe went through a whole bunch of doublings of size.

Dr. Pamela Gay: Yeah. Yeah.

Fraser Cain: You know, imagine if all of your atoms decided they were going to go through a, or the space between your atoms decided they were going to go through a doubling several times in a fraction of a second.

Dr. Pamela Gay: This is where when the universe did this, when everything was pure energy, you didn’t have to worry about atoms getting held together or torn apart. And so now theorists have to like worry about things like, so what forces are going to be the greater forces? We know that currently gravity is stronger than whatever is pushing our universe apart.

And so things that are gravitationally bound stay gravitationally bound. We know that in general, things that structurally hold devices together through electromagnetic effects. Atomic forces.

Fraser Cain: These are all, right. These are all way stronger than the forces that are trying to push them apart.

Dr. Pamela Gay: But what happens if inflation happens again?

Fraser Cain: Yeah.

Dr. Pamela Gay: Yeah. Yeah.

Fraser Cain: That, that, that your, the gaps between your atoms go through a series of doublings.

Dr. Pamela Gay: And this is where there, there are as many theories as you can stick theorists into a room and then multiply it a few times because some of those people are going to have more than one possible theory. And so we, we don’t know what would happen if we aren’t actually at a zero point energy. And the other side of this is the idea that there’s this background energy created by the summation of all of these different wavelengths across space kind of gets us back to the idea of ether.

And that’s just weird that everything goes full circle sometimes.

Fraser Cain: Right. Maybe that’s, that’ll be a different show. So, so is that vacuum decay, what you just described?

Yeah. Okay. Right.

And so let’s say, and, and you know, the more space you have, and if this is a probability than the bigger the universe gets, that there is a higher and higher chance that this could happen somewhere randomly across the universe, that some part of the universe could hatch upon a new idea to collapse down to a lower energy state. So what would happen next?

Dr. Pamela Gay: So this is where you start getting into all sorts of people attempting to imagine things without understanding necessarily what timescales things are going to happen on. And you end up with a very similar problem with the idea of two universes in a bubble multiverse that have different physics colliding and merging. You can imagine the difference rippling through space.

And if it is slow enough, you basically see part of the universe go weird and then you die.

Fraser Cain: But it would move at the speed of light. It couldn’t go faster than the speed of light. Could it?

Dr. Pamela Gay: No. But it could go slower than the speed of light.

Fraser Cain: Yikes.

Dr. Pamela Gay: Yeah.

Fraser Cain: Right. And so, so if I guess the worst case scenario is it goes at the speed of light. And so the moment that you find out that this is happening, you’re undergoing inflation.

But maybe a more horrific version of that is that you actually watch the universe getting torn apart as it approaches you at close to the speed of light. Let’s say neutrino speed as opposed to light speed.

Dr. Pamela Gay: Yeah. Yeah. Neutrino speed would still be hard to see.

But yeah, we don’t know these things.

Fraser Cain: Right.

Dr. Pamela Gay: There’s so many things we don’t talk about that we don’t know. We don’t know how to quantify gravity. We don’t know how to explain the fact that we have this fits on a grid like it was designed by a board computer programmer graph of particle physics.

It’s looking like supersymmetry isn’t real. Basically, folks at the LHC are now finally willing to say, look, we should have found it by now. We have not give up.

Now do string theory. So there’s all these things that kind of are predicated on each other. Understanding the full nature of the particle zoo, understanding how to quantify gravity, if it’s quantifiable.

All of these things fit together as a whole. And until we understand that whole, we can’t fully understand the consequences of universes colliding of having the background energy level of the universe drop from one level to another through vacuum decay. Yeah.

So we are at this fabulous point of knowing questions, not knowing answers and being able to make stuff up.

Fraser Cain: So how do we take advantage of this stuff? I mean, if there’s that much energy packed into every cubic meter of the universe, you know, Stargate, they had the zero generator.

Dr. Pamela Gay: Right.

Fraser Cain: How do you how do you extract energy out of the cosmos itself?

Dr. Pamela Gay: I, I’m just an observer. This isn’t something we’ve figured out yet. I’m a sci-fi fan, but this isn’t something we’ve figured out how to do beyond being able to say, yes, there’s a Casimir effect.

It’s really hard and expensive to prove it’s there, but it’s there. I think we’re better off figuring out how to do productive vision first.

Fraser Cain: Right. As opposed to attempting to extract and who knows what kind of disastrous outcomes could come, like talk about a tragedy of the commons where we drop the universe down to. Is that the Fermi paradox?

Is that the is that the is that the great filter?

Dr. Pamela Gay: I don’t think it’s the great filter, but but I mean, this is one of the problems with particle physics is there’s always this concern that we’re going to do something profoundly wrong and many good sci-fi novels are predicated on this idea where you start to imagine the big one that I think got the most publicity is the when they turned on the Large Hadron Collider to do the Higgs boson search. There was the well, what if we create microscopic black holes that fall to the center of the Earth and begin devouring the planet?

And it turns out it’s not really a problem. They eat very, very slowly. That one I did run the math for.

I was teaching physics at the time. It was far too much fun.

Fraser Cain: Right. That the science that predicts them also predicts that they will have evaporated before they even hit the ground.

Dr. Pamela Gay:

And even if they don’t evaporate, which would have been cool because it could have allowed Hawking to finally get the Nobel Prize. But if you also run at figuring out he was wrong, they don’t evaporate. They’re not problematic.

They eat very slowly. They’re very tiny. They mostly just split between atoms going high.

I’m a black hole.

Fraser Cain: The thing that I love with that whole thing was that there are cosmic rays hitting the atmosphere with more energy than the LHC is capable of producing. And so we are already in a natural particle accelerator that is greater than anything humanity has currently built, but not necessarily what humanity might eventually build. There will come a day when someone proposes a particle accelerator that is more powerful than anything that’s ever been detected by the universe.

And then we are truly in unforeseen territory. And maybe that’s when we destroy the universe. Thanks, Pamela.

Dr. Pamela Gay: Yeah. Yeah. Some nights, some days that seems like the correct output.

Fraser Cain: We brought this around to an apocalypse, which is your favorite subject.

Dr. Pamela Gay: It’s excellent. It’s excellent. All right.

Thank you all so much. Thank you for helping Fraser keep universe today going. Thank you all of you who also support CosmoQuestX and allow me to keep everything going over there.

This show is also supported by Patreon. Everything we do, Fraser, myself, this show, we’re supported by you. This week, I’d like to thank the following humans.

Sergio Sansevero, Bill Smith, Brett Moorman, Jarvis Earle, Slug, G. Caleb Sexton, Andy Moore, Evil Melky, Breznik, Andrew Allen, Cody Ross or Cody Rose, rather, Brian Cook, Robi the dog with the dot, Kate Sindretto, Helga Bjorkog, Steven Veidt, Christian Magerholt, Andrew Palestra, Gerholt Schweitzer, ZeroChill, Les Howard, Gordon Dewis, Kim Barron, Katie Byrne, Masa Herleu, Alex Cohen, Matt Rucker, Andesor, Steven Coffey, Michael Regan, Diane Philippon, Philip Walker, Sean Matz, Cooper, Sam Brooks and his mom, Jeff Wilson, Matthias Hayden, Kami Rassian, Glenn McDavid, Kim Garish, Robert Cordova, David Bogarty, John Fays, Christian Golding, Frank Stewart, Time Lord Iroh, Jim of Everett, Sergei Manilov, Conrad Hailing.

Thank you all so very much.

Fraser Cain: Thanks, everyone. And we’ll see you next week.

Dr. Pamela Gay: Bye-bye.

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A map of Earth’s gravity. Red indicates areas of the world that exert greater gravitational pull, while blue indicates areas that exert less. A science-grade quantum gravity gradiometer could one day make maps like this with unprecedented accuracy. Image Credit: NASA

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Using clouds of ultra-cold atoms as test masses is ideal for ensuring that space-based gravity measurements remain accurate over long periods of time, explained Sheng-wey Chiow, an experimental physicist at JPL. “With atoms, I can guarantee that every measurement will be the same. We are less sensitive to environmental effects.”

Using atoms as test masses also makes it possible to measure gravity with a compact instrument aboard a single spacecraft. QGGPf will be around 0.3 cubic yards (0.25 cubic meters) in volume and weigh only about 275 pounds (125 kilograms), smaller and lighter than traditional space-based gravity instruments.

Quantum sensors also have the potential for increased sensitivity. By some estimates, a science-grade quantum gravity gradiometer instrument could be as much as ten times more sensitive at measuring gravity than classical sensors.

The main purpose of this technology validation mission, scheduled to launch near the end of the decade, will be to test a collection of novel technologies for manipulating interactions between light and matter at the atomic scale.

“No one has tried to fly one of these instruments yet,” said Ben Stray, a postdoctoral researcher at JPL. “We need to fly it so that we can figure out how well it will operate, and that will allow us to not only advance the quantum gravity gradiometer, but also quantum technology in general.”

This technology development project involves significant collaborations between NASA and small businesses. The team at JPL is working with AOSense and Infleqtion to advance the sensor head technology, while NASA’s Goddard Space Flight Center in Greenbelt, Maryland is working with Vector Atomic to advance the laser optical system.

Ultimately, the innovations achieved during this pathfinder mission could enhance our ability to study Earth, and our ability to understand distant planets and the role gravity plays in shaping the cosmos. “The QGGPf instrument will lead to planetary science applications and fundamental physics applications,” said Hyon.

To learn more about ESTO visit: https://esto.nasa.gov

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Apr 16, 2025

Editor NASA Science Editorial Team Contact Gage Taylor gage.taylor@nasa.gov Location NASA Goddard Space Flight Center

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Categories: NASA

NASA Aims to Fly First Quantum Sensor for Gravity Measurements

NASA - Breaking News - Tue, 04/15/2025 - 2:51pm