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The stars that stretch across the night sky have captivated human imagination for centuries, inspiring entire mythologies. They are a magnificent sight, and after reaching the moon, it seems natural that the next step might be to venture to the stars. Interstellar travel is a key element in many science fiction tales, leading many to believe that it could be an imminent reality. However, there are still significant obstacles that must be overcome before such a journey can be undertaken.
10. Breaking the Light Barrier
In many fictional works, there are wild theories about how faster-than-light travel could work. The unfortunate truth is that the laws of physics make this impossible. There are no shortcuts. Even approaching light speed presents numerous relativistic challenges, especially regarding mass and energy. The only theoretical way forward would be to utilize wormholes. However, these would need to be precisely controlled, something far beyond our current technological capabilities. Moreover, creating a second wormhole at the desired destination would require an advanced team at the other end, which isn’t practical for the first interstellar mission. To make matters worse, traveling through a wormhole could physically destroy anything that enters, turning it into plasma by the time it reaches the other side.
9. Teleportation
The traditional concept of teleportation involves a person activating a device, vanishing from one location, and reappearing instantly at another. However, this process is far more complex than it seems. The individual’s atoms are broken down in the teleportation device, transferred to the destination, and then reconstructed. This requires a teleportation machine already set up at the destination, as current physical laws prevent us from manipulating matter so precisely over the vast distances between stars. Therefore, teleportation could only be feasible for places that have already been explored. While reassembling a person is theoretically possible, it remains beyond our capabilities. Furthermore, the atoms would still need to travel across space, which, although potentially faster than traveling as a whole body, would still take years. For instance, the nearest star to the sun is four light years away, meaning it would take at least four years for any matter to reach it. Another option would be for the reassembly machine to have a reserve of atoms to recreate the individual, but this would essentially mean creating a copy and destroying the original, a concept many would find uncomfortable.
8. Generation Ships
If faster-than-light travel is unattainable or unfeasible, we may consider the option of generation ships. Although light can reach the nearest star in just four years, heavy objects would take much longer. In fact, most stars are hundreds of years away. Generation ships are designed to house a population for many generations, with the descendants eventually reaching the destination. However, there are significant challenges with this approach. As time passes, the original mission could be forgotten, becoming more of a myth for future generations. A sophisticated computer system might help preserve the mission’s purpose, but predicting the long-term behavior of successive generations is increasingly uncertain. If the ship encounters a problem, a population that has regressed over centuries could find itself helpless.
7. Egg Ships
To reduce the uncertainties associated with generation ships, egg ships could be considered. These would transport frozen human eggs, which would then be nurtured by specially-designed machines acting as both parents and educators. Upon reaching the distant star or planet, the eggs would be grown into fully-formed humans, who would be educated by computers on their mission, survival, and how to proceed. While creating machines capable of raising these humans without stunting their emotional development is beyond our current capabilities, it may become possible in the future. However, like with generation ships, egg ships don't provide a solution for those who wish to personally travel to the stars. The idea of waiting for artificially-raised humans to fulfill the dream of reaching the stars long after one’s own death is unacceptable to many.
6. Longevity
An alternative to using a generation ship is to genetically modify people to live for hundreds or even thousands of years, allowing them to complete the journey within their own lifetimes—assuming, of course, that the challenges of living in space are resolved. Both longevity and immortality are significant areas of scientific exploration, but they face a major hurdle: telomeres. Telomeres are protective caps at the ends of our DNA that shorten each time our cells divide. Eventually, as telomeres wear down, cells start to damage their own critical DNA during division. This process limits the number of divisions our cells can undergo. Cells divide to replace aging or damaged ones, such as those in our skin or the lining of the stomach. The potential solution lies in maintaining telomeres, but currently, only cancerous cells have this ability.
5. Stasis
When longevity and generational ships are not feasible, many sci-fi stories turn to the concept of suspended animation for long journeys. In this state, people do not age or age very slowly, essentially entering a form of hibernation. However, telomeres again present a significant issue. Our bodies naturally contain small amounts of radioactive elements that emit tiny amounts of radiation. These are normally harmless because our cells replace any damaged ones. But if a person is kept in stasis and does not age, their telomeres don’t shorten, and their cells cannot divide. This leads to a dangerous buildup of radiation damage in the body, and given enough time, it could be fatal. Even with slow aging, the radioactive damage would accumulate over time, as we rely on normal cell division to repair and replace damaged cells.
4. Propulsion
Even if the challenges of human space travel to distant stars were overcome, the issue of propulsion still remains. Traditional methods rely on burning fuel or reaction mass, but to reach another star, astronomically large amounts of fuel would be required. One potential solution is to collect fuel along the way. In the vast emptiness between stars, there are no convenient asteroids or planets to mine for resources. Fortunately, space isn't completely empty; it's filled with scattered atoms, mostly hydrogen. By traveling at high speeds, these atoms could be gathered and used as fuel in an efficient reaction like fusion—assuming we can master fusion in the future. To collect these atoms, a massive scoop would be necessary, with estimates placing its size at over 2000 square km. This would severely hinder the ship’s speed, making it slower than the space shuttle, and would create immense drag. Furthermore, this system is highly inefficient and impractical, especially given that our sun is located in a relatively sparse part of space, providing a poor fuel source.
3. Food, Air, and Water
Any humans aboard a spaceship for extended periods of time will require life support systems. They need food, water, air, waste disposal, hygiene, and sleep. Many of these needs have already been addressed in previous space missions. However, on longer journeys, the quantity of food and water required becomes impractical to transport. The most likely solution is to transform the spacecraft into a self-sustaining ecosystem. Plants could produce oxygen, be consumed as food, and process human waste. While no ecosystem is perfectly efficient, such a system might be able to sustain the crew long enough to reach its destination. Over time, the spacecraft’s equipment could degrade due to the recycling of gases, but with intelligent maintenance or new materials, this problem might be mitigated. The most effective system might involve a single type of plant, such as algae, which has been extensively studied for its potential. Spirulina algae, in particular, is a candidate for this role. It could handle air production, waste recycling, and food production. However, it is not a complete food source and can be toxic if contaminated or consumed in large amounts. Genetic engineering may improve its safety and nutritional value in the future.
2. Gravity
The human body is fundamentally reliant on gravity for its structure. Without the pull of Earth's gravity, we begin to experience negative health effects. After a few weeks or months, bones become fragile and muscles weaken, with more severe long-term consequences. These issues can be somewhat alleviated through exercise and diet, but prolonged space travel—spanning years or even decades—results in irreversible damage to the human body. Even short-term space flights can lead to significant eyesight deterioration, which NASA has identified as a major obstacle that must be overcome before sending humans to Mars. To simulate gravity in space, spacecraft can be rotated to create centrifugal force. However, this requires enormous amounts of energy and fuel, and the immediate side effect is nausea. The long-term impacts of this artificial gravity are still unknown, but they are expected to be problematic.
1. Damage
The nearest star system to us is Alpha Centauri, located just four light years away. If we were to travel at the speed of an average car—60 km/h—it would take an astonishing 72 million years to reach it. Even if we somehow overcame all the challenges mentioned before, such an extended journey is practically impossible due to the natural wear and tear on the spacecraft, not to mention the extremely low likelihood of completing such a trip. Speed is essential, even if it's limited by the speed of light. However, the vast emptiness of space is filled with minuscule atoms that, when a ship moves at high velocities, collide with the spacecraft with such force that they would penetrate even the strongest materials, causing holes in the ship. This presents two potential solutions: either humans or machines would need to constantly repair the ship, which would require enormous quantities of repair materials, or the ship would need to be constructed from self-healing, elastic materials. The good news is that NASA has researched such materials. The bad news is that, according to their findings, these materials are not currently viable.
