Elon Musk’s plans refer to an idea conceived in the 1960s. What is the Kardashev scale?

By Jacopo Prisco, CNN

(CNN) — Elon Musk’s plans for the future of SpaceX, and humanity, are rooted in an idea conceived in the 1960s when astronomers began to pick up mysterious, unknown radio sources in the cosmos.

Soviet astronomer Nikolai Kardashev was a pioneer in the search for extraterrestrial intelligence at the time, and some of the signals fascinated him. Intrigued by the idea that a transmission from potential alien civilizations could possibly be detected from Earth, he proposed a scale to classify such civilizations based on the energy they could produce — and then devote to interstellar communications. His concept is now known as the Kardashev scale.

Musk has referenced the scale often, most recently in video shared on X, his social platform, ahead of SpaceX’s blockbuster initial public offering in June and in a signed statement on the company’s website, which summarizes a request filed this year with the US Federal Communications Commission.

In the request, SpaceX asks for permission to send up to 1 million new satellites into orbit, with the goal of creating data centers in space. Musk said that this new constellation of satellites would represent “a first step towards becoming a Kardashev II-level civilization.”

The Kardashev scale has three levels, moving from planet to star to galaxy. A Type I civilization can use all the energy of a single planet, either produced by the planet itself — for example in the form of geothermal or wind power — or received from its host star, like solar power. A Type II civilization can use the entire energy output of a star, as well as send information across galactic distances. A Type III civilization can harness the power of a whole galaxy and send information across multiple galaxies.

The Kardashev scale has its detractors, but it has been a catalyst for discussion for the past six decades, and the subject of many revisions that have added extra levels of categorization. Experts have recognized the framework as a useful tool to grade potential civilizations, albeit one that is not used in any official capacity.

“The Kardashev scale is, in principle, almost the only scientific framework we have for objectively assessing a civilization’s technological level, specifically in terms of its ability to harness and utilize energy,” said Zaza Osmanov, an affiliate of the SETI Institute and associate dean of the School of Physics at the Free University of Tbilisi in Georgia. “More precisely, it allows us to estimate and compare the scale of energy resources that a civilization can control and exploit.”

Judging by that standard, any alien civilization that were to happen upon Earth now likely wouldn’t be too impressed, Musk suggested in the video SpaceX shared last month. But could the company’s plans for orbital data centers, which face a number of technical hurdles, and its ongoing development of Starship, the most powerful launch system ever built, really change that view? Even if they did, experts say continuing to level up in the Kardashev sense could be complicated — and consequential.

Earth on the scale

Kardashev first published the scale in a 1964 scientific paper titled “Transmission of Information by Extraterrestrial Civilizations,” and it soon became the subject of scrutiny.

“In the 1960s the idea that we could communicate with alien species was all rather new, and everyone was trying to figure out how possible it was,” said Jason Wright, a professor of astronomy and astrophysics at Penn State University. “Nikolai Kardashev was a young radio astronomer who got very excited about this idea, and he started thinking about a new type of radio source that had recently been discovered. We now understand them to be supermassive black holes in the centers of galaxies — quasars — but at the time they were still trying to figure out what they were.”

Without precisely specifying where Earth sat on his scale, Kardashev described Type I as a “technological level close to the level presently attained on the Earth.”

American astronomer Carl Sagan proposed a revision of the scale in the 1970s to address what he believed was a major flaw: a lack of subtlety. Sagan added decimal points to make the scale continuous and suggested that humanity was about a Type 0.7 on his new version. It’s important to note, however, that Sagan’s version of the scale — which has become influential in its own right — is not linear but logarithmic, meaning that the gap between 0.7 and 1 is much larger than it may appear at first glance.

“The Kardashev scale is often criticized because it tries to project our understanding of human history and progress onto aliens,” Wright said, “but Sagan’s version allows us to simply set all of that aside and say species use some amount of energy, and this is how we describe how much energy they use. In that way, I think it is useful.”

The most recent approximation of where Earth sits on the adapted Kardashev scale comes from a 2023 study. Using economic, demographic, climate and ecological variables, it estimates that humanity is currently a Type 0.7276. The study also projects that by 2060, humanity would reach Type 0.7449, or about a 50% growth in energy consumption.

Technically, any energy project adds to Earth’s position on the scale, but the road to full Type I is a long one. “Under current energy and technology trends, reaching Type I civilization status would likely take millennia, unless major breakthroughs such as large-scale renewable expansion or nuclear fusion substantially change the trajectory,” said Antong Zhang, lead author of the 2023 study and a visiting researcher at the Harvard John A. Paulson School of Engineering and Applied Sciences.

With humanity still short of reaching Type I status, is aspiring to become a Type II even possible? According to Musk, “Any self-respecting civilization should at least reach Kardashev Type II.” That doesn’t necessarily mean that Earth needs to fully achieve Type I, but rather “a first attempt at using space-based solar energy harvesting,” according to Zhang.

According to Wright, Musk’s plan to launch 1 million satellites is technically a step toward Type II, but harnessing the entire power of the sun would require materials totaling more mass than all the asteroids in the asteroid belt. Such a move could fundamentally alter the structure of the solar system and the habitability of Earth.

“This is not a realistic or desirable goal for humanity to be pursuing,” Wright said.

Going off-planet

Detractors of the Kardashev scale say that even reaching Type I status is not actually a realistic goal.

“Nobody really wants to use all the energy of a planet, because you would completely destroy the planet in the process,” said Philip Metzger, a planetary physicist and a research professor at the University of Central Florida who had an extensive career at NASA. “My view is we don’t use any more of the Earth’s energy. I’ve been arguing for a couple of decades that we need to move industry off the planet.”

Echoing Musk’s approach, Metzger said he believes that the future of energy production and industrial manufacturing should be in space or on the moon, essentially leapfrogging Type I to aim directly at Type II.

“I wrote a paper back in 2012 when I was still with NASA, and it got attention from the Obama White House and we had a series of meetings about it,” Metzger said. “The paper was arguing that we can actually start a solar system-level civilization rapidly by putting factories on the moon and bootstrapping those factories, and we argued it would take somewhere in the range of 20 to 70 years, depending on how fast you go, and it would pay back tremendous benefits to the world while costing about a third of NASA’s budget.”

Metzger acknowledges that this proposal “sounds like science fiction” and is “kind of crazy,” and also that there’s currently no political mandate for it. However, he added, that view could change because the demand for artificial intelligence is making data centers an extremely profitable business venture but also one vehemently opposed over concerns about power and water consumption. Moving the data centers off-planet could be an answer to those concerns, he said.

Living in space is also becoming a popular idea, at least among billionaires. Amazon founder Jeff Bezos has openly supported the concept of “O’Neill colonies,” orbiting structures that would be miles wide and each hold up to 1 million people, using resources such as frozen water that can be harvested from the moon.

If Type II civilizations exist somewhere in our galaxy, there could be ways to spot them. One is to look for hypothetical superstructures called Dyson spheres, which were a familiar concept to Kardashev as they had been imagined by American physicist Freeman Dyson in 1960.

A Dyson sphere or swarm is a shell made up of mirrors or solar panels that completely surround a star, harnessing all the energy it produces. Such a structure would inevitably give off waste heat detectable as infrared radiation, so scientists have theorized that looking for that byproduct could be a viable method for searching for extraterrestrial life.

A study published in 2024 looked at 5 million stars in the Milky Way galaxy and found seven candidates that could potentially be hosting Dyson spheres.

“What that showed is that if Dyson spheres exist, they are extremely rare, so we now know that this is not a common phenomenon in our galaxy,” Wright said. The candidates are nevertheless “very interesting” and more observations are underway, he added, to find out more about them using the James Webb Space Telescope — although they might simply turn out to be false positives, or not really Dyson spheres.

“There is a possibility that some other galaxy has been filled with Dyson spheres as a Type III. We’ve done some work to try and see if that’s the case,” said Wright, talking about a forthcoming study that aims to ascertain “whether these things are common in the universe or not.”

The search for alien signals

When it comes to the possibility of extraterrestrial life, most scientists will exercise caution.

“The existence of Type II or Type III civilizations is certainly plausible in principle, given the age and scale of the universe,” said Tomo Goto, an associate professor of astronomy at the National Tsing Hua University in Taiwan, in an email. “However, the lack of observational evidence for such civilizations suggests that they are either extremely rare, short-lived, or fundamentally different from what the Kardashev framework assumes.”

Ever since American astrophysicist Frank Drake launched Project Ozma, the first search for alien signals, in 1960, there has been no shortage of similar projects, and technological progress is constantly improving their reach and scope.

“In my view, a Type II civilization is entirely plausible,” Osmanov said. “In fact, detecting a civilization at our current level — or even a Type I — may be more difficult.” That’s because, Osmanov explained, other stars in our galaxy are on average much older than the sun, so if civilizations emerged around those stars, they would have had enough time to become far more advanced than humanity.

But what would an alien species be doing with all the energy from an entire star? “We do not know the exact purpose, but what human history suggests is that as our ancestors progressed to higher levels of intelligence and technological development, their overall energy consumption increased,” Osmanov said.

“I would expect something similar in this case: a highly advanced civilization would probably not remain confined within a single planetary system, which implies large-scale utilization of space and a corresponding demand for energy, potentially exceeding our current energy consumption by many orders of magnitude.”

Kardashev, who died in 2019 after an illustrious scientific career, followed up on the scale with two papers, published in 1980 and 1985. These suggested strategies to spot signals coming from intelligent civilizations and dealt with the possible implications of such a discovery for humanity. Even though his scale focuses on energy production, he believed that “the concepts of morality and goodness are universal, like the Pythagorean theorem. Civilizations do not survive if they do not follow these concepts.”

“The Kardashev scale is a useful thought experiment for classifying civilizations in terms of their energy consumption,” Goto said. “However, it is important to keep in mind that more advanced civilizations may prioritize efficiency, computation or information processing rather than simply increasing total energy usage.”

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