# Why is interstellar travel so hopelessly difficult?

• B
• Ranvir
In summary, TRAPPIST-1 is a system 40ly away from Earth, and the muons in our upper atmosphere show that it may be closer than we think. It is hard to estimate the time it would take to get there, as the distance and speed involved are small. However, the energy requirements to reach this far are horrific, and even a highly efficient fusion torch drive would have a hard time doing this.
Ranvir
So, I have been thinking about TRAPPIST-1 and how far away that system is from us. It is 40ly away from Earth, according to our frame of reference. This is often put in a way that makes one think that even at speeds close to that of light, it will take almost 40 years to get there.

The muons in our upper atmosphere, on the other hand, show something different. Even though they are short lived, unstable particles they often make it to the surface of the Earth just because of their high velocities. Here length contraction/ time dilation makes them survive long enough( Or brings us closer to them).

Won't the same argument work for human subjects, traveling at relativistic speeds?
The distance between them and TRAPPIST-1 would be so small that they may finish it in a couple of years, depending on their precise speeds.

I don't know, if I am missing something here, except the Earth's reference frame where it is inevitably 40 years, but the astronaut might not be that discomforted by the journey, at the end of the day. (Feel free to throw quantitative arguments and maths to make your point, if you want to)

Last edited by a moderator:
You have it right - the traveller can experience arbitrarily short time if they can tolerate the acceleration. But the energy requirements to accelerate even a small mass to near light speed are horrific. Google for "relativistic rocket" if you want the depressing details - even total conversion drives need (from memory) millions of times the mass of the payload in fuel.

Ranvir
Ibix said:
You have it right - the traveller can experience arbitrarily short time if they can tolerate the acceleration. But the energy requirements to accelerate even a small mass to near light speed are horrific. Google for "relativistic rocket" if you want the depressing details - even total conversion drives need (from memory) millions of times the mass of the payload in fuel.
I live in horrific details, thanks for that ;)
However, what used to confuse me were the articles claiming, it would take me almost 40 years to get there even at light speed or 99.9% of it. I don't even care if my rocket gains so much mass because of high velocity that it turns to a black hole, tbh :P

You can get there and back in arbitrarily short time by your own clocks, but it will inevitably have taken 80+ years by Earth's clocks. Whether that means that it takes 80 years or no time at all depends on your application. If you ask your love to wait for your return (you'll only be gone a few minutes!) you may be disappointed.

A word of advice - forget you ever heard the phrase "relativistic mass". It causes all sorts of confusion. For example, the idea that your rocket might turn into a black hole. http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_fast.html

Ibix said:
A word of advice - forget you ever heard the phrase "relativistic mass". It causes all sorts of confusion. For example, the idea that your rocket might turn into a black hole. http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_fast.html
Thanks, it actual cleared a lot of air. It raises more questions too, but I guess, I might have to crack open a few books and sort them out for myself.

Battlemage! and Ibix
Another issue is that at high relativistic speeds, collisions with small particles in the interstellar void could be catastrophic. Then there is the need for shielding from cosmic gamma rays. Etc. ... Many impediments for our current state of technology.

A ship using a constant 1g acceleration half-way toward its destination, and then applying the same 1g acceleration to slow down for the other half can travel 40 light years in about 7.3 years of traveler time. If you made a round trip, You'd experience about 14.6 years, but about 83.8 years would pass on Earth. Rockets that can apply 1g of acceleration are well within our grasp. Rockets that can do this for years at a time, however, are far beyond reach at this point. So, the main problem we have to tackle for relativistic space travel is the ability to apply a useful amount of thrust for long periods of time practically. Even a highly efficient fusion torch drive would have a hard time doing this.

## 1. Why is interstellar travel so hopelessly difficult?

Interstellar travel is difficult because of the vast distances and extreme conditions that exist in space. The nearest star to Earth, Proxima Centauri, is over 4 light years away, meaning it would take over 4 years to travel there even at the speed of light. Additionally, the harsh radiation and lack of resources in the vastness of space make it challenging for humans to survive long journeys.

## 2. Can't we just use faster-than-light travel to make interstellar travel easier?

Unfortunately, the laws of physics as we currently understand them do not allow for faster-than-light travel. The theory of relativity states that nothing can travel faster than the speed of light, and even if we were able to achieve such speeds, the amount of energy required would be immense. Additionally, the concept of time dilation would make it difficult for humans to survive such high speeds.

## 3. What about cryogenic freezing or suspended animation for long interstellar journeys?

While these are popular ideas in science fiction, the technology to safely and effectively freeze and revive humans for long periods of time does not currently exist. Even if it did, the challenges of maintaining a stable environment and dealing with the effects of radiation and lack of resources in space would still make interstellar travel difficult.

## 4. Are there any current efforts to make interstellar travel a reality?

Yes, there are ongoing research and development projects focused on making interstellar travel possible. Some involve developing new propulsion systems or spacecraft designs, while others are exploring the potential for using advanced technologies such as antimatter or black holes. However, these efforts are still in the early stages and it may be many years before we see any significant progress.

## 5. Is it possible that there are other civilizations in the universe that have mastered interstellar travel?

It is certainly possible that there are advanced civilizations in the universe that have developed the technology and knowledge to travel between stars. However, the vastness of space and the limitations of our current technology make it difficult for us to detect or communicate with these civilizations. The search for extraterrestrial life and potential interstellar travel are ongoing areas of research and exploration in the scientific community.

• Special and General Relativity
Replies
21
Views
1K
• Special and General Relativity
Replies
7
Views
1K
• Special and General Relativity
Replies
63
Views
3K
• Special and General Relativity
Replies
65
Views
5K
• Sci-Fi Writing and World Building
Replies
6
Views
859
• Special and General Relativity
Replies
60
Views
3K
• Special and General Relativity
Replies
83
Views
3K
• Special and General Relativity
Replies
6
Views
1K
• Special and General Relativity
Replies
15
Views
7K
• Special and General Relativity
Replies
56
Views
3K