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How will we travel to another star?

Proxima Centauri, our closest star, is more than 4 light years away. Reaching it under 10,000 years will be challenging; reaching it with living humans will be even harder.

NASA
  • Eventually, humanity will want to travel to a new solar system to propagate the human race, explore, and maybe find signs of alien life.
  • But our closest neighbor, Proxima Centauri, is so far away that current methods could take tens of thousands of years.
  • How will we surmount this incredible distance and the other challenges associated with interstellar travel?

Alpha Centauri, the closest star system to our own, isn't actually close at all. While light takes 8 minutes to travel from the sun to Earth, it takes 4.37 years to travel from Proxima Centauri — that system's star — to Earth. That's all well and good for light, but human beings can't go quite so fast. Voyager 1 passed the boundaries of our solar system at around 37,000 miles per hour, which seems pretty fast. This speed, though, is only 1/18,000th the speed of light; were Voyager 1 pointed towards Proxima Centauri, it would take 80,000 years.

This is a problem. If humanity is to survive in the long term, we need to become a multiplanetary species. And while we may be able to terraform other planets in our own solar system to become new homes, we will eventually need to travel to other stars. Equally important, we want to do so in order to learn more about our universe, satisfy our curiosity, and maybe even find alien life. But before we can, we'll have to surmount some pretty significant challenges.

Distance

Proxima Centauri as viewed from the Hubble telescope.

NASA

Right now, we just don't have any good methods of propelling a spacecraft at the necessary speed for interstellar travel. In order to travel far and fast, we need to carry lots of fuel. But the more fuel we carry, the more mass we need to propel through space, making the use of on-board fuel reserves for a rocket exponentially more challenging for long journeys.

Most modern spacecraft use a mixture of liquid hydrogen and liquid oxygen as fuel, but this certainly wouldn't work for a trip to Proxima Centauri. NASA presented a quick scenario where we aimed to arrive at Proxima Centauri in 900 years with a conventional, chemical rocket without slowing down when we got there (which a real manned mission would certainly want to do). Using this method, there wouldn't be enough matter in the universe to fuel our rocket.

So, we would need a new method. There are a few different candidate technologies that we could pursue, each of which deserves its own separate article to examine fully: there's antimatter engines, warp drives, laser-powered light sails, and many others.

However, warp drives are entirely speculative; humanity has only succeeded in producing a little less than 20 nanograms of antimatter, and making a gram of antimatter would cost a million billion dollars; and laser-powered light sails would require a steady power source equivalent to what the Earth consumes in a day. The most likely initial engines for getting us to our stellar neighbor will probably rely on nuclear fusion, and they'll probably need to host human life for decades, if not centuries.

Project Daedalus, a British Interplanetary Society study, examined the feasibility of this approach and found that a fusion-powered spacecraft could accelerate to 12 percent the speed of light, then cruise for a period of time before slowing down prior to reaching a distant star. If we could pull this massive undertaking off, a fusion rocket could reach our closest stellar neighbor in just 36 years, compared to the tens of thousands of years other methods would require. Unfortunately, the kind of fuel we would use (helium-3) is extremely rare on Earth, the project would cost about $5.267 trillion, and the study focused on unmanned missions. A spacecraft that could support human life would be significantly more difficult to design.

Collisions

NASA

If we travel anywhere through space at significant fractions of the speed of light (almost certainly a requirement for interstellar travel), then impacting interstellar dust or larger objects like space debris or micrometeoroids could be disastrous. Even in the short trips we made during the space shuttle program, more than 100 shuttle windows were replaced after being chipped or cracked by space debris. Traveling to Proxima Centauri would be over a 100 million times the distance, and we'd almost certainly run into something.

Fortunately, actual asteroid collisions would be fairly rare. If we were to encounter any large obstacles, the same Project Daedalus that conceived of a fusion-powered spacecraft proposed using drones to eject small particles that would sweep those obstacles away. It's also been suggested that magnetic superconductors could divert the smaller dust particles away from a hypothetical spacecraft.

Health

Image source: Wikimedia Commons

The technical challenges of interstellar travel also extend to the problem of how to preserve our mental and physical health. Outside of Earth's protective magnetosphere, cosmic radiation can cause dementia and damage cognitive function as well as cause cancer. Fortunately, magnetic superconductors such as the one's mentioned above may be able to protect against dangerous cosmic radiation.

There are also the challenges associated with low-gravity environments. Without gravity, our bones' density drops by 1 percent per month, our muscles atrophy, and the risk of developing vision problems and kidney stones increases. If a spaceship were to constantly accelerate, it could mimic Earth's gravity, but this would require more fuel, driving up the cost and engineering challenges associated with a hypothetical interstellar project.

Alternatively, we could develop a rotating spacecraft whose centripetal force simulates gravity. But again, this brings up additional engineering challenges. A rotating spacecraft would need to supply extra energy to maintain the rotation, complicated seals and motors would need to be placed between the rotating and non-rotating components, and the structure of the ship would need to be stronger (and thus heavier) to prevent it from flying apart over time.

The mind and the unknown

Image source: NASA

With enough research, we can see a path forward to solving all of these issues. But the biggest challenges may be less clear cut. How do we prevent human beings trapped on a spaceship for decades from completely losing their minds? Even after arrival, how will they contend with the idea that they most likely will never return to Earth and may never see new human beings again?

And then, there's always the unknowns. We can plan, mitigate, develop redundancies and innovations, but there will always be something unanticipated, especially in a project whose primary goal is to explore the unknown. But then again, the reason why we explore at all is to learn more about the currently mysterious.

Neom, Saudi Arabia's $500 billion megacity, reaches its next phase

Construction of the $500 billion dollar tech city-state of the future is moving ahead.

Credit: Neom
Technology & Innovation
  • The futuristic megacity Neom is being built in Saudi Arabia.
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Tuberculosis vaccine shows promise in reducing COVID deaths

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Closeup of a BCG vaccination.

Credit: Kekyalyaynen.
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Human brains remember certain words more easily than others

A study of the manner in which memory works turns up a surprising thing.

Image Point Fr / Shutterstock
Mind & Brain
  • Researchers have found that some basic words appear to be more memorable than others.
  • Some faces are also easier to commit to memory.
  • Scientists suggest that these words serve as semantic bridges when the brain is searching for a memory.

Cognitive psychologist Weizhen Xie (Zane) of the NIH's National Institute of Neurological Disorders and Stroke (NINDS) works with people who have intractable epilepsy, a form of the disorder that can't be controlled with medications. During research into the brain activity of patients, he and his colleagues discovered something odd about human memory: It appears that certain basic words are consistently more memorable than other basic words.

The research is published in Nature Human Behaviour.

An odd find

Image source: Tsekhmister/Shutterstock

Xie's team was re-analyzing memory tests of 30 epilepsy patients undertaken by Kareem Zaghloul of NINDS.

"Our goal is to find and eliminate the source of these harmful and debilitating seizures," Zaghloul said. "The monitoring period also provides a rare opportunity to record the neural activity that controls other parts of our lives. With the help of these patient volunteers we have been able to uncover some of the blueprints behind our memories."

Specifically, the participants were shown word pairs, such as "hand" and "apple." To better understand how the brain might remember such pairings, after a brief interval, participants were supplied one of the two words and asked to recall the other. Of the 300 words used in the tests, five of them proved to be five times more likely to be recalled: pig, tank, doll, pond, and door.

The scientists were perplexed that these words were so much more memorable than words like "cat," "street," "stair," "couch," and "cloud."

Intrigued, the researchers looked at a second data source from a word test taken by 2,623 healthy individuals via Amazon's Mechanical Turk and found essentially the same thing.

"We saw that some things — in this case, words — may be inherently easier for our brains to recall than others," Zaghloul said. That the Mechanical Turk results were so similar may "provide the strongest evidence to date that what we discovered about how the brain controls memory in this set of patients may also be true for people outside of the study."

Why understanding memory matters

person holding missing piece from human head puzzle

Image source: Orawan Pattarawimonchai/Shutterstock

"Our memories play a fundamental role in who we are and how our brains work," Xie said. "However, one of the biggest challenges of studying memory is that people often remember the same things in different ways, making it difficult for researchers to compare people's performances on memory tests." He added that the search for some kind of unified theory of memory has been going on for over a century.

If a comprehensive understanding of the way memory works can be developed, the researchers say that "we can predict what people should remember in advance and understand how our brains do this, then we might be able to develop better ways to evaluate someone's overall brain health."

Party chat

Image source: joob_in/Shutterstock

Xie's interest in this was piqued during a conversation with Wilma Bainbridge of University of Chicago at a Christmas party a couple of years ago. Bainbridge was, at the time, wrapping up a study of 1,000 volunteers that suggested certain faces are universally more memorable than others.

Bainbridge recalls, "Our exciting finding is that there are some images of people or places that are inherently memorable for all people, even though we have each seen different things in our lives. And if image memorability is so powerful, this means we can know in advance what people are likely to remember or forget."

spinning 3D model of a brain

Temporal lobes

Image source: Anatomography/Wikimedia

At first, the scientists suspected that the memorable words and faces were simply recalled more frequently and were thus easier to recall. They envisioned them as being akin to "highly trafficked spots connected to smaller spots representing the less memorable words." They developed a modeling program based on word frequencies found in books, new articles, and Wikipedia pages. Unfortunately, the model was unable to predict or duplicate the results they saw in their clinical experiments.

Eventually, the researchers came to suspect that the memorability of certain words was linked to the frequency with which the brain used them as semantic links between other memories, making them often-visited hubs in individuals's memory networks, and therefore places the brain jumped to early and often when retrieving memories. This idea was supported by observed activity in participants' anterior temporal lobe, a language center.

In epilepsy patients, these words were so frequently recalled that subjects often shouted them out even when they were incorrect responses to word-pair inquiries.

Seek, find

Modern search engines no longer simply look for raw words when resolving an inquiry: They also look for semantic — contextual and meaning — connections so that the results they present may better anticipate what it is you're looking for. Xie suggests something similar may be happening in the brain: "You know when you type words into a search engine, and it shows you a list of highly relevant guesses? It feels like the search engine is reading your mind. Well, our results suggest that the brains of the subjects in this study did something similar when they tried to recall a paired word, and we think that this may happen when we remember many of our past experiences."

He also notes that it may one day be possible to leverage individuals' apparently wired-in knowledge of their language as a fixed point against which to assess the health of their memory and brain.

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