So I was thinking about crafting a hard science-fiction campaign setting: no “vhoosh” or “pew pew pew” noises in space, no faster-than-light starships, no artificial gravity, no friendly aliens, no “wibbly-wobbly, timey-wimey stuff” like teleportation or time travel. What “do’s and don’ts” factor into that kind of sci-fi?
LIGHT SPEED AND SUBLIGHT TIME DILATION: Faster-than-light travel for material objects (like starships) is impossible without some “magic” alternative (like “warp drives,” or “jumping into hyperspace,” or “stargate” wormholes). Approaching the speed of light at slower (“sublight”) speeds risks dealing with the effects of time dilation, the difference in time measured between two objects moving at different relative velocities. (Technically, it’s the difference in gravitational potential, but you get the idea.) For the difference to matter to a casual observer, the velocity of one object would have to exceed half lightspeed (0.5c), where 1 “local” day on the moving object would equal 1.15 days compared to the an object “at rest” (like a planet in normal space). At 0.7c, one “starship” day would be 1.4 days in normal space, or 1.67 days at 0.8c, or 2.29 days at 0.9c. At velocities above 0.9c, the difference increases quickly: 1 day aboard a ship moving at 0.99c equals about a week planetside, and at 0.000c, 1 day aboard equals 22 days in normal space.
From user samiles on Github: https://gist.github.com/samiles/bc27066b7a8d6f0eb3a7b61f54c54f99
"""
This script calculates the time dilation experienced during a space journey given the
velocity, acceleration, and duration of the journey.
The script uses the astropy package to handle units and time calculations.
Args:
velocity (float): Velocity of the spaceship as a fraction of the speed of light.
acceleration (float): Acceleration of the spaceship in units of g0.
duration (float): Duration of the journey in years (from the perspective of a clock on earth).
Prints:
Date on Earth at departure
Date on spaceship at journey end
Date on Earth at journey end
Lorentz factor
Time dilation factor
Time interval on spaceship
More Info:
https://samiles.com/blog/2023/02/calculating-time-dilation-in-space-travel-with-python/
"""
import argparse
from astropy import constants as const
from astropy import units as u
from astropy.time import Time
import warnings
from astropy.utils.exceptions import AstropyWarning
# Ingore warnings about odd dates
warnings.simplefilter('ignore', category=AstropyWarning)
# Parse command line arguments
parser = argparse.ArgumentParser(description='Calculate the time dilation experienced during a space journey.')
parser.add_argument('velocity', type=float, help='velocity of the spaceship as a fraction of the speed of light')
parser.add_argument('acceleration', type=float, help='acceleration of the spaceship in units of g0')
parser.add_argument('duration', type=float, help='duration of the journey in years')
args = parser.parse_args()
# Set up input parameters
v = args.velocity * const.c # velocity of the spaceship
a = args.acceleration * const.g0 # acceleration of the spaceship
duration = args.duration * u.yr # duration of the journey
earth_time = Time.now() # Define starting time on Earth (as the current time)
# Calculate the Lorentz factor, using the formula γ = 1 / sqrt(1 - v^2/c^2)
gamma = 1 / (1 - (v / const.c) ** 2) ** 0.5
# Calculate the time dilation factor
dilation_factor = 1 / gamma
# Calculate the time interval measured on the spaceship
delta_t = dilation_factor * duration
# Calculate the date on the spaceship
ship_time = earth_time + delta_t
# Calculate the date on Earth after journey ends
earth_time_after = earth_time + duration
print('Date on Earth departure:', earth_time.iso)
print('Date on spaceship at journey end:', ship_time.iso)
print('Date on Earth at journey end:', earth_time_after.iso)
print('Lorentz factor: {:.2f}'.format(gamma))
print('Time dilation factor: {:.2f}'.format(dilation_factor))
print('Time interval on spaceship: {:.2f}'.format(delta_t.to(u.yr)))
Under this example, a spaceship able to maintain 1G acceleration could reach a planet in the Alpha Centauri system (on average about 4.3 light years away) in roughly 5.3 years of travel. Heading to a planet in the Epsilon Eridani system (10.52 ly away) takes 11.52 years, while a trip to a planet in the Tau Ceti system (11.89 ly away) takes 11.8 years from the standpoint of Earthlings. To the crews of these spaceships, time would take much less due to time dilation effects.
THE COLD VACUUM OF SPACE: Technically “outer space” vacuum is very cold (say, 2.7 Kelvin in the shade), but without matter to conduct heat, objects cool down very slowly. However, in direct sunlight (or similar energy from another G-class star), things absorb energy and heat up very quickly. “Space” can be very cold or very hot, or both at the same time, depending on local conditions and exposure. A human exposed to the vacuum of space would become unconscious in about 15 seconds due to air forced from lungs and a lack of oxygen in the bloodstream. Moisture on the skin and in the mouth would vaporize (“boiling away”). Death would occur in minutes due to lack of oxygen, likely a worse factor than tissue damage due to extremes of cold or heat. Finally, a corpse floating in space would never decompose since the microorganisms responsible for rot also die off. If you find a bare skeleton inside a broken spacesuit floating in space, it was like that before it ended up in a vacuum. Those who have survived exposure to space – namely, astronauts like Kevin Ford and Don Pettit who performed space walks for NASA – describe a particular odor from space: an “acrid aroma of seared steak, hot metal and welding fumes.”
GRAVITY ISSUES, PART 1: Artificial gravity aboard a spaceship is impossible without some “magic” alternative (like “contra-grav” plate under the floor), but there are two natural physical means of simulating the 1G pull experienced at sea level on Earth (9.8 meters per second squared). The first option is “centrifugal force,” the apparent force that seems to push an object outward when it is rotating around a central point or along a curved path. In other words, make a spaceship or space station spin around an axis. To achieve 1G, a larger radius would require a slower rotation speed, while a smaller radius would need a faster rotation speed to generate the same force. Here’s the math:
# Given values
g = 9.81 # acceleration due to gravity in m/s^2 (1G)
radius = 100 # radius in meters
# Centripetal acceleration formula: a = v^2 / r
# We want a = 1G, so solve for v (velocity)
# v = sqrt(a * r)
velocity = math.sqrt(g * radius)
velocity # in meters per second
Based on these calculations, a hoop or ring-shaped space station of 1 km radius would need to be rotating at just under 100 meters per second (or 360 kph, or 224 mph) to exert 1G of force on its “floor,” and central hallways would slope “up” forward and behind someone walking its circumference. If this ring was 100 meters wide, the whole structure would be just short of 0.6 square kilometers, almost double the area of New York City’s 104-floor One World Trade Center skyscraper. Also note another hoop or ring rotating in the opposite direction (a counter-rotating ring) would stabilize a spinning space station by counteracting the effects of angular momentum and gyroscopic forces.
The second natural option would be to travel in space at a constant 1G acceleration, rather than using “bursts” of thrust to change velocity. The “down” of the moving ship would be in the direction of thrust, while “up” would be toward the forward/front/”top” of the ship. To reach a specific destination, a ship would have to accelerate at a constant rate for half its journey, then flip 180 degrees and decelerate for the remainder of the trip. For long distances, this acceleration might get the object approaching high sublight speeds, making time dilation an issue (see above). It would take a spaceship about 7.1 years at 1G acceleration to reach 0.99c velocity, during which time 7.8 years would have passed at its point of departure.
import math
# Constants
c = 299792458 # Speed of light in meters per second
# Function to calculate velocity
def relativistic_velocity(a, t, c=c):
return c * math.tanh(a * t / c)
# Example usage
a = 9.8 # Example acceleration (in meters per second squared)
t = 10 # Example time (in seconds)
v = relativistic_velocity(a, t)
print(f"Velocity: {v} m/s")
GRAVITY ISSUES, PART 2: What if a human crew went along in space without simulated gravity? Several health issues become a problem: Regular bodily functions become “confused,” causing a human heart to weaken, spine to lengthen (taller but risk of nerve pain), bone and muscle mass to atrophy, and a body’s ability to process insulin changes. Humans would always suffer nasal congestion (“stuffed up running nose”), ruining almost all sense of taste. A person’s ability to recognize when it is time to pee would grow difficult, and smelly farts don’t float away – they linger. Exposure to radiation penetrates skin directly to the retinas of the eyes (people always see light), and such energy also causes cells to mutate more quickly. Microorganisms are also affected, causing bateria to change and mutate. A human immune system could quickly become compromised against such new germs, and previously reliable medicines and vaccines would lose their potency. A human who somehow became accustomed living in weightlessness would have a difficult time getting use to gravity (objects don’t simply float wherever to last left them, and walking feels odd).
GRAVITY ISSUES, PART 3: Without friction, there’s nothing to slow down a moving body. Any ship unable to change its own velocity will continue at it’s current speed and direction until passing through the gravitational pull of another object (or colliding into something). The space opera cliche of a crippled spaceship “floating dead in space” only happens if the ship was already standing still when its propulsion system became inoperable. “Catching up” to a helpless ship moving at any velocity would require a much faster ship.
THE COLOR OUT OF SPACE: Most “photographs” people on Earth have seen of stars, nebula, and other cosmic objects have been artificially colorized by artists. In reality, many stellar objects only give off non-visible light in the infrared, ultraviolet, x-ray, and gamma spectrums – meaning the “space” outside a spaceship’s window is always going to look dark. Also, the distances between cosmic objects is vast, even when considering things that look dense from far away. For example, the Cassini Division “gap” in Saturn’s rings is about 4,800 km wide – and even the “rings” themselves are just bands of particles a few meters apart. That said, tiny meteoroids moving at incredibly high speeds can deliver a sudden and devastating amount of energy when colliding with spacecraft, satellites, or humans floating in space. Accumulations of cosmic dust can also build up overtime to cause wear and mechanical failure over time.
DEATH RAYS FROM SPACE: In terms of non-visible energy, outer space is filled with potentially harmful radiation that people on Earth are naturally protected against. An “M-class world” (“Earth-like”) has an atmosphere and magnetic field that minimizes exposure, a luxury those in the void of space don’t get to enjoy. Then there are risks from whatever energy source a spaceship might be using for its own power systems. Solar flares and coronal mass ejections (CMEs), bursts of solar energy and plasma from a nearby sun or star, can interfere with electronics, communication systems, and spikes in radiation exposure.
ALIEN LIFE: Forget about “little green men” or near-humans evolving on exoplanets. The Fermi paradox states that living creatures – and particularly, advanced extraterrestrial life – should be common considering the abundance of chemicals and conditions across the universe. So why has humanity not made known contact with anyone else? Author Liu Cixin offered up one theory in his book The Dark Forest: Aliens already do exist throughout the universe, but they remain silent and hidden to avoid being found and destroyed by another hostile and undetected civilization. (The strong and superior always conquer and consume the weak and inferior.) If that case is true, then humanity’s noisy blasts of radio waves may be Earth’s death knell.
Else, life may be abundant, but humanity hasn’t noticed it yet. Earth-bound notions of carbon-based complex molecular beings formed organically by proteins and enzymes might be just one form of life. Biologies based on silicon, ammonia, nitrogen, or phosphorus are theoretically possible, as are lifeforms evolving from environments rich in sulfur, boron, or arsenic. Plasma-based or energy-based life forms could theoretically exist in high-energy environments such as stars or gas giants. Such beings may have been trying to communicate with humanity for centuries by modulating gamma rays or putting mathematical patterns into other signals that so far the people of Earth have mistaken for cosmic noise.
Alien lifespans may also be a factor. Human years, decades, and centuries may be too brief a span of time to notice for beings with lifespans measured in millions of years, or far to too long for nanosecond creatures whose generations evolve, mature, and go extinct in the span of a Earthly afternoon.
It’s also worth speculating about lifeforms made up of forms of energy and matter that humanity has yet to discover – such as “the Craven Dark Matter Triangles of 1,200mHz” – but now we’re talking about unknown “magic” to explain the sci-fi, which I’m avoiding here.