I hear a lot of people say that looking at our universe from a solar system, galactic, or cosmological scale makes them feel small and insignificant. Insignificant to who and what? I look at our universe and I see the incredible complexity that has arisen from a few forces and a few fundamental laws. You see it in the structure of the cosmic background, you see it in the shapes of galaxies, you see it in the heavy elements formed in our stars. Nowhere do you see that complexity more than when you look at life. It was a glorious accident that allowed us to exist, and we exist in an incredibly delicate balance.
99.99999999…% of the universe is empty space. 99.9999999…% of that which is not empty space is lifeless. Why does it matter if somewhere light years away something doesn’t care about your individual existence? We have this amazing planet and it might not be unique in the universe in its complexity, but it is incredibly rare and special, and I feel very significant — overwhelmed with a sense of purpose and duty, in fact — because it is up to us to try as hard as we can to preserve this rare and special place and all the life on it.
The structure of the universe doesn’t make me feel insignificant. It makes me feel incredibly lucky. By some chance I exist in this rare place. Thus it is my duty to try to keep life existing here, and to try to make that life as pleasant as possible for the other rare and lucky creatures who share it with me.
– Jenn Seiler, astrophysicist and Universe Sandbox ² developer.
Learn how we simulate Earth’s climate and how you can explore it in Universe Sandbox ²:
What is the n-body problem?
The n-body problem can be defined as “the problem of predicting the individual motions of a group of celestial objects interacting with each other gravitationally.” Or, in a gravitational system of n bodies (where n can be any number), where will they all be after one year?
It’s helpful to frame this in contrast to the two-body problem, which looks at the motion of just two objects interacting with each other. For example, you can look at the Earth and Moon as a two-body problem. The Earth pulls on the Moon quite a bit, keeping it in orbit, and the Moon pulls on the Earth just a little bit.
The issue here is that the Moon is not affected gravitationally by just the Earth; it is also being pulled by the Sun, and Jupiter, and every other object in space. The same is true when looking at the Sun and Earth: the Sun is not the only object pulling on Earth. So to account for all of these gravitational forces, you need to use an n-body solution.
The problem of the n-body problem in Universe Sandbox ²
In Universe Sandbox ², every object is simulated as part of an n-body problem. Unfortunately, when solving for many objects, or n objects, you can’t just jump forward in time without getting massive errors. There’s simply no way around this. Solving an n-body problem requires calculating how each object affects each other object every step of the way. Errors will still happen, but taking smaller steps reduces them.
By default, the simulations in Universe Sandbox ² try to set an accuracy which prevents orbits from falling apart due to error. This means setting a maximum error tolerance for each step and also making sure the total error doesn’t reach an upper limit.
If you crank up the time step, the simulation then has to take fewer, larger steps. This means the potential for greater error. And the greater the error, the more likely it is that an orbit, which otherwise would be stable, falls apart. Moons crash into planets, Mercury gets thrown out of the solar system — things like that.
This isn’t what most people want in their simulations. But at the same time, most people also don’t want a limit on how fast they can run their simulation. This is a problem.
An imperfect solution
So how can we get around this problem? How can we accurately simulate thousands of objects while still allowing for large steps forward in time? For example, what if you wanted to simulate our solar system on a time scale of millions of years per second so that you could see the evolution of our Sun?
One solution proposed by Thomas, our physics programmer, is to allow for a special mode within simulations running at high time steps. This mode (which of course could be toggled) would collapse the existing n-body simulation into a series of 2-body problems: Moon & Earth, Earth & Sun, Europa & Jupiter, Jupiter & Sun, etc.
Solving a 2-body problem is much easier than solving an n-body problem. Not only is it faster computationally, but there is also a relatively arbitrary difference between figuring out where the two objects will be in one year and where they’ll be in a million years — it still requires just one calculation. So if you collapse an n-body simulation into a series of two-body problems, the simulation could take one big step forward, instead of taking the small steps needed for calculating it as an n-body problem.
The results won’t be entirely accurate, as this method would effectively ignore all gravitational influences outside of the main attractor. As mentioned before, calculating Earth’s orbit by looking at how it interacts with just the Sun is not accurate, as Earth is also affected by every other body. The Sun, however, is the most significant factor by far, because it is much more massive than any other object in our solar system. The other, much smaller forces tend to have little effect overall in non-chaotic systems. So while it’s not correct, it’s close enough when simulating something relatively stable like our solar system.
This isn’t a perfect solution. But we think it could be an improvement over the current system and its limitations, which leave you with the choice of either destabilizing the orbits with massive errors, or waiting days for the simulation to advance the millions of years needed for the Sun to evolve. Neither is particularly interesting.
When is this coming to Universe Sandbox ²?
Not anytime soon.
This solution is just a proposed idea right now, and is not a high priority for us, as we already have a big list of exciting features planned. But we think it is useful to understand the complexity of accurately simulating the motions of hundreds to thousands of objects interacting gravitationally.
This is especially a challenge when attempting to do this in real-time on a home computer, which is why researchers run numerical simulations on supercomputers which take days to complete. With Universe Sandbox ², we’re exploring new territory and working through problems which haven’t been solved before. And this is a big part of why we love making it.
What’s the significance of discovering gravitational waves?
This announcement is a huge deal. It is on par with the discovery of the Higgs Boson particle which provided the missing evidence for a prediction of the Standard Model of particle physics. Gravitational waves are a century-old (almost exactly) prediction now confirmed by a huge number of relentless, and brilliant people after many years of hard work. It is the first direct confirmation of the prediction from Einstein’s General Relativity that matter and energy determine the motion of bodies by warping the fabric of spacetime itself, and in so doing, emanate ripples when massive bodies are accelerated through that space.
It is not only confirmation of general relativity, though. It is also the first of many future observations that will look at the universe in a completely new way. Up until now we’ve used only photons (telescopes all along the electromagnetic spectrum) and sometimes neutrinos. Now we can add listening to the fabric of space to our list of tools. This will allow us to see the dark and the obscured parts of the universe: the early universe, centers of galaxies, things blocked by dust clouds, and so on, by listening for changes in space itself. It is the start of a new age in astronomy.
In addition to this detection being the first direct proof that the predictions of general relativity that matter and energy warp space time are true, and some of the strongest evidence for the reality of black holes, this is also a new kind of astronomy. Though gravity is the weakest force and gravitational waves are very hard to detect, they do have a few advantages over observations of photons.
- First, gravitational waves are practically impervious to matter in their path. This means we can see into regions of space that are blocked to optical observatories, such as inside dense clouds of dust, the centers of galaxies, behind large or close bodies.
- Second, this is an observation of the warping of space itself, meaning we can detect things that have mass but might not produce observable light, such as black holes, dense sources of dark matter (if such were to exist), cosmic string breaks, etc.
- Third, gravitational waves fall off in amplitude much more slowly than light. This means that we can receive signals from very far away that we might not notice optically.
- And fourth, because gravitational waves also travel at the speed of light and don’t have to bounce off intervening matter, and begin to be potentially detectable from bodies getting close rather than just after the moment of collision, this means that we can work with other telescopes and tell them “Look over there! You’re probably going to see something exciting!”
This all of means that this detection means the beginning of a new kind of observational astronomy, as well as a better understanding of of of the fundamental forces of the universe, gravity.
What role did Jenn, astrophysicist and Universe Sandbox ² developer, play in the discovery?
While I was in the field I ran super-computer simulations to make predictions about the gravitational wave signals that would be produced by binary black hole mergers. Those waveforms are used as templates in the detector pipeline. The detector matches the template banks against the incoming data to find real signals amidst the noise of the detector, while also doing searches for large burst signals (how this one was found). Those waveforms are then used again to determine where the signal came from, what it was (two black holes, a neutron star and a black hole, two neutron stars, etc), and the properties of the bodies that created the signal (spins, masses, separation, etc.). I also worked on developing the analytical formulas to determine those spins and masses from those signals.
Here’s one of the scientific papers on the process of determining the properties of the source of the signal, with three papers cited on which Jenn Seiler was an author:
The Einstein equations for general relativity are ten highly non-linear partial differential equations. This means that it is only possible to obtain exact solutions for astrophysical situations for some very idealized conditions (such as spherical symmetry and a single body). In order to predict the gravitational waveforms produced by compact multi-body systems, or stellar collapse, it is necessary to solve the equations numerically (computationally). This means formulating initial data for spacetimes of interest (such as two in-spiralling black holes of various spins and mass ratios) and evolving them by integrating the solutions of the Einstein equations stepping forward in time by discrete steps. To prove that these computer simulations approximate reality more than just by equations on paper we would run these simulations at multiple resolutions for our discrete spacetimes and show that our solutions converged to a single solution as we approach infinite resolution (that would represent real continuous space) at the rate we expect for the method we were using.
There were many obstacles in creating these simulations: vast amounts of computational power required for accuracy; the fact that we needed to run tons of these large, slow, computationally intensive simulations in order to cover the parameter space (spins, masses, orientations, etc) of potential sources of gravitational waves; and so on. For black holes, one major challenge was the fact that they contain a singularity. A singularity means an infinity, and computers don’t like to simulate infinities. Numerical relativity researchers had to find a way to simulate black holes without having the singularity point in the slicing of the spacetime integrated in the simulation. The first successful simulation of this kind didn’t happen until 2005 (http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.95.121101).
Once we had working simulations, groups around the world set to work on simulating the gamut of major potential gravitational wave signal sources. These simulation results were not just useful to the detectors to help identify signals, but also to the theorists to help formulate predictions about the results of such astrophysical events. Predictions such as: the resulting velocity of merged black holes from binaries of various spins, the amount of energy released by black hole mergers, the effect that black hole spins have on the spins and orbits of other bodies, etc.
When will you add gravitational waves into Universe Sandbox ²?
We really can’t do gravitational waves in an n-body simulation, which is the method Universe Sandbox ² uses to simulate gravity. N-body simulations look at the effect that each body has on each other body in a system at small discrete time steps.
General relativity requires simulating the spacetime itself. That is, taking your simulation space, discretizing it to a hi-res 3-D grid and checking the effect that each and every point in that grid has on all neighboring points at every timestep. Instead of simulating N number of bodies, you are simulating a huge number of points. You start with some initial data of the shape of your spacetime and then see how it evolves according to the Einstein equations, which are 10 highly non-linear partial differential equations. Accurate general relativity simulations require supercomputers.
There are some effects and features related to relativity that would be possible to add to Universe Sandbox ², however. Here are a few we are discussing:
Gravity travelling at the speed of light.
Currently if you delete a body in a simulation, the paths of all other bodies instantly respond to the change. The reality is that it would not be instantaneous; it would take time for that information about the altered gravitational landscape to reach a distant object.
Spinning black holes.
Most black holes are very highly spinning. If you imagine a spinning star collapsing it is easy to understand why. This is the same effect as when a spinning figure skater pulls in their arms; because of conservation of angular momentum, they spin faster. A consequence of this spin is that, while the event horizon would remain spherical, there would be an oblate spheroid (squished ball) around the black hole called an ergosphere. This ergosphere twists up the spacetime contained within it and accelerates bodies that enter this region (as well as affecting their spins). Because it is outside of the event horizon, this means one can slingshot away from this region and even steal energy from the rotation of that black hole.
Corrections to the motions of bodies to approximate general relativity.
Loss of momentum due to the emission of gravitational waves causes close massive bodies to inspiral. With this you could recreate the decaying orbits of binary pulsars.
Spins of close bodies affect each other’s motion and spins (see above). This would give you things like spun up accretion disks around black holes.
These corrections would be made by adding post-newtonian corrections to body velocities.
The discovery of a hypothetical ninth planet in our solar system was announced on January 20th, 2016 by researchers at the California Institute of Technology.
Universe Sandbox ² Alpha 18.2 features two simulations of Planet Nine. Run Steam to update, then check them out in Home -> Open -> Possible Planet Nine [and] Evidence of a Ninth Planet.
Or buy now for instant access to Universe Sandbox ² on Steam Early Access:
The announcement comes after years of research into explaining the peculiar, but very similar, orbits of six small bodies orbiting beyond Neptune. Many theories have been proposed, but none has been as compelling as a very distant ninth planet pulling these bodies into their highly elliptical orbits. Using mathematical modeling, the two researchers, Konstantin Batygin and Mike Brown, have shown that a ninth planet fits very well into the data we have about objects in the Kuiper Belt and beyond.
Planet Nine has not been directly observed yet by telescope, which is why it is hypothetical. But the researchers say there is a very good chance of spotting it in the next five years. It is suspected to be about 10 times the mass of Earth, similar in size to Neptune, with an orbit that’ll take it around the Sun every 10,000 – 20,000 years.
Of course, we don’t know how Planet Nine got there. Brown and Batygin propose that this planet was formed in the early days of the solar system, along with Jupiter, Saturn, Uranus, and Neptune. Then it could have been shot outward by one of the gas giants, and instead of leaving the solar system entirely, it may have been slowed down by gas in the Sun’s protoplanetary disk, enough to keep it in orbit.
If the ninth planet does exist, then it will be the second time our solar system will have claim to nine planets… After, of course, Pluto was demoted in 2006. But Brown says there’s no question that the hypothetical ninth planet is indeed a planet. It’s likely much bigger than Earth, and has a large influence on other bodies in the solar system. And besides, Brown would know — his discovery of Eris was the reason Pluto was voted out.
Here’s a great discussion of Planet Nine by Mike Merrifield, an astronomer and professor at the University of Nottingham:
We’re hope you’re as excited about this possible discovery as we are! Make sure you check out the new simulations in Universe Sandbox ²: Home -> Open -> Possible Planet Nine [and] Evidence of a Ninth Planet.
See the complete list of What’s New in Alpha 18.2: What’s New
Additional links about Planet Nine:
An Unpredictably Long Winter is Coming
Fans of George R. R. Martin’s fantasy series A Song of Ice and Fire or the television series, Game of Thrones, know well the often repeated warning, “Winter is coming.”
For those living on the continent of Westeros in this fantasy world, summers can be long, and so can the winters. But some winters are especially cold and last for several years, while others are relatively mild and short.
What causes this variance in seasons? Martin doesn’t offer an explanation, so we’re free to speculate.
Simulating Westeros in Universe Sandbox ²
The paper may be tongue-in-cheek, but that doesn’t mean we can’t use its parameters to try simulating it in Universe Sandbox ². Like the paper, we were unable to find stable orbital parameters that would create the level of unpredictability discussed in the books or the show.
We could, however, create a system that has variable winter and summer intensities on regular predictable intervals with a large northern polar ice region. Though our results didn’t exactly match those in the paper, we managed to recreate similar seasonal patterns to what the authors describe in their paper.
If you own Universe Sandbox ², you can see this simulation for yourself in Alpha 15: Home -> Open -> Fiction -> Lands of Ice & Fire | Game of Thrones.
To open the temperature graph, open the Westeros planet’s Properties, select the Climate tab, hover over the Surface Temperature icon and click the Graph button.
If you don’t own Universe Sandbox ², you can buy it now to get instant access to the alpha via Steam code: http://universesandbox.com/2
First observed in 1970, Earth Day now gathers over 1 billion people in 192 countries every year on April 22 to celebrate our planet and raise awareness of the issues it faces. According to Earth Day Network, that makes it the largest civic observance in the world.
The growth of this movement toward the care and appreciation for our planet is evident all around us. Environmental awareness is no longer reserved for activists and radicals. “Going green” and “reducing your footprint” have become familiar, if not trendy, concepts.
But despite this, human-caused climate change continues to take us further down the road toward inevitable crisis. It’s a bleak forecast, but one that we, as individuals, nations, and a global community, must confront if we want to create the necessary changes.
Earth in Universe Sandbox ²
In Universe Sandbox ², we’ve added a simple climate simulation for Earth. We hope it helps in understanding how our climate works, and how fragile our planet is.
Here are a few things you can try in Universe Sandbox ²:
Simulate Future Climate Scenarios
- We’ve included the ability to simulate scenarios based on data from the most recent IPCC report
- We recommend trying the Climate Scenarios activity (Home -> Main tab)
- You’ll learn how to use the different models and graph Earth’s temperature over time
- Learn more about simulating these scenarios in our previous blog post
Tidally lock the Earth to the Sun
- Select Earth (in the default Solar System sim)
- In Earth’s properties window, click the “Motion” tab
- Scroll down and click “Tidally Lock”
- Now one side of the planet will always face the Sun
- And the other side of the planet will begin to freeze over
- Tidal locking is why there’s a “dark side of the moon.” From here on Earth, we can only ever see the same side
- Try moving the Earth closer to the sun to turn it into a comet.
- Or move the Earth out past Mars and watch it freeze over. (Load the sim “Earths Next to Sun” to see multiple Earths at various distances from the Sun)
If you don’t own Universe Sandbox ², you can get instant access to the alpha through our website: universesandbox.com/2
One of the most important features in Universe Sandbox ² is the ability to simulate Earth’s climate. It’s a relatively simple simulation, but it helps demonstrate exactly how fragile and ever-changing our climate is.
In Alpha 13, you can select possible future scenarios for Earth’s climate. These scenarios simulate the rise in carbon dioxide levels in Earth’s atmosphere caused by human activity up until the year 2100.
To simulate these, we use the same Representative Concentration Pathways used in the latest report from the Intergovernmental Panel on Climate Change (IPCC). These four pathways are projections for the future of greenhouse gas emissions and resulting concentrations in our atmosphere. You can see each pathway’s projections in the graphs below (left: emissions; right: concentration).
There are many factors we can consider when looking at what changes will affect emissions. Policies, land use, global population, our attitudes toward production and consumption — these can all have a huge impact on greenhouse gas emissions. Each RCP makes different assumptions about how and when these factors might change.
To stabilize concentrations, decreases in emissions are required, because even when emissions are lowered, CO₂ hangs around in the atmosphere for a long time.
Not only do the scenarios project different outcomes for concentrations, but, importantly, they each follow a unique trajectory based on a range of possible socio-economic changes. One assumes a peak in greenhouse gases in the next decade, while another assumes that there will never be stabilization. (This is simplified for the sake of this introduction; you can learn more here.)
In Universe Sandbox ², you can enable RCPs by selecting the Climate tab in Earth’s properties and toggling “Select an RCP Scenario.” The default is RCP 8 5. Click the (+) icon to select one of the other 4 scenarios.
Once enabled, the pathway’s concentration level will be tied to the simulation year. The change in net radiative energy balance is also specified by the scenarios, and we put that right into our energy balance as a decrease in outgoing infrared energy. This has the effect of increasing the greenhouse effect and ultimately increases the average temperature of the planet. To see how the different scenarios play out, you can graph Earth’s temperature over the course of several decades. Below is a simulation of RCP6 through 2100.
These pathways are not forecasts. But simulating them in Universe Sandbox ² can help you gain a more intuitive understanding of what is possible for the future of Earth’s climate.
You can also check out the climate tutorials right in Universe Sandbox ²: Home -> Main -> Activities.
In this video, Chad, our technical artist, demos his recent work on shaders which simulate atmospheric scattering (in real-time, of course).
Atmospheric scattering is a process in which particles in a planet’s atmosphere scatter sunlight. It is the reason why the sky is blue, and why the setting sun is red.
Please note: This video is a demo created by Chad; it is not from Universe Sandbox ². Atmospheric scattering is an experimental feature still in its early stages. Do not expect to see this implemented in an alpha release anytime too soon.
More information on atmospheric scattering:
If you do not yet own Universe Sandbox ², you can buy it now to get instant access to the alpha, as well as free updates up to and including the final release: universesandbox.com/2.
Have you seen Interstellar? Without revealing too much of the plot… the sci-fi film follows a group of astronauts who search the depths of space in hopes of finding a new home for the human race.
The film’s special effects team worked with astrophysicist Kip Thorne in order to create visual effects that were not only beautiful representations of our universe, but were also founded on accurate science (Wired article).
One phenomenon they wanted to simulate was a massive black hole with an accretion disk. What they ended up with is certainly impressive:
Turns out, if you add rings to a black hole in Universe Sandbox ², you get something that looks pretty similar:
Of course, you’ll notice a few differences between these images. But that might be because the first image is from a pre-rendered animation made for a film with a $165 million budget, and the second is from a real-time, interactive simulation that can run on your home computer.
If you don’t yet own Universe Sandbox ², buy it now to get instant access to the Alpha through Steam as well as free updates up to and including the final release: universesandbox.com/2
The video below was created by Eric, an astronomer working on Universe Sandbox ².
You will be able to try out these new features for yourself in an upcoming alpha of Universe Sandbox ².
If you do not yet own Universe Sandbox ², you can buy it now to get instant access to the alpha, as well as free updates up to and including the final release: universesandbox.com/2.