# Tag Info

14

That's basically the Fermi paradox. It seems likely that there are numerous civilizations in the galaxy, and yet we see no trace of them anywhere. The Drake equation is often invoked to calculate the probability of existence of other civilizations, by compounding several other, more simple probabilities: the probability that a star has planets, that the ...

10

Yes. As has been commented, the amount of damage taken by an interstellar spaceship depends on its velocity $v$, as well as the number of gas and dust particles that it encounters on its way. This number is usually measured per area, in which case it's called column density $N$, and is equal to the total distance $d$ traveled times the particle density $n$, ...

8

I'll start with the second question first: Also, do we exactly know about each and every object inside our solar system? Each and every object? Of course not. That however is irrelevant to the question at hand. The vast majority of objects in our solar system are very, very small. Quite literally as small as dust. But because they're so small, they have ...

7

Possible rendezvous with a Kuiper belt object and Voyager type data on the heliosphere: "We should have power until the 2030s, so we can get into the outer part of the heliosphere," says Spencer. "As long as we can continue to get good data—and persuade NASA to pay for it—we will keep getting the data, because we will be in a unique environment that we've ...

7

The equation for Doppler shifting towards the blue spectrum (i.e. when you are traveling towards it) is: $\lambda_b = \lambda_c/(c + v_b)$ where $\lambda_b$ is the shifted wavelength, $\lambda_c$ is the original wavelength, $c$ is the speed of light and $v_b$ is your velocity towards the source. BUT! When you get closer to the speed of light you need to ...

6

The answer is in your question. You said there couldn't be any (meaningful) forces interacting between them to provide any sort of way to travel through it. That's the great thing about outer space. There normally aren't many particles around that could slow down a spacecraft via drag or friction. If you give something a push in outer space - somewhere ...

6

I'd like to know a little more about the geometry of the ship's trajectory. I would be asking for clarification in comments but I don't know how to put images in comments. A good distance away the ship is moving nearly a straight line with regard to the large mass. As the ship gets closer the path gradually bends towards the large mass. If you're still a ...

6

The brightness of the spaceship follows (almost) the inverse square law, meaning twice the distance from the star, the brightness will be a quater. In the middle of nowhere, but within a galaxy, it would look like in a moonless, and cloudless night, far away from any artificial light source. It wouldn't be pitchblack, but much too dark to read a newspaper. ...

6

Stars and gases at a wide range of distances from the Galactic center orbit at approximately 220 kilometers per second. From Wikipedia That's much faster than the Voyager probes relative to the Sun (Voyager 1: 17 km/s). Hence the probes will orbit the galactic center roughly the same way as our Solar System, even after occasional hyperbolic encounters with ...

5

"Yes, but no." If you could jump through space faster than light can travel, and you went 1 light year away to 'look back at earth', then you would observe the light emissions that began 1 year ago, and continue to observe them as they arrive. [And if you start moving towards or away from the emission source, then 'neat things' happen due to blue/red shift. ...

5

Sort of. But not the same system. Here's a photo of the directions the two Voyager probes (and a couple Pioneers) are traveling: They're also not traveling in a flat plane, as this page says: Voyager 1 has crossed into the heliosheath and is leaving the solar system, rising above the ecliptic plane at an angle of about 35 degrees at a rate of about 520 ...

4

If you notice carefully, you'll see that their speeds away from the sun are fairly similar (7-9 km/s), and the difference is only in their speeds away from the earth. This is because of a small component of earth's motion around the sun (which is at about 30 km/s) adding to Voyager 1's motion and subtracting from Voyager 2's motion.

4

You aren't missing anything. The pulsar map is fairly useless unless the spacecraft is found within the next million years, when it won't have got too far from the Sun (the probes will have travelled about 30 light years in that time). The problem is not so much that the set of pulsars won't be visible, because they almost certainly would be if you change ...

3

You could do better than that. You could walk around on a younger earth. This Physics.SE Q&A addresses why. The short of the matter being that things are moving with respect to each other, and so have different inertial reference frames. Your ability to travel faster than light lets you exploit the differing reference frames to conduct a round trip ...

3

I was fortunate enough to spend the past week at a workshop held at the Green Bank Observatory (GBO), so I can give you a partial answer based on how the Breakthrough Initiatives affects it in particular. Telescope time The GBO actually operates a selection of telescopes, of which the most widely-known (and largest) is the Green Bank Telescope (GBT). The GBT ...

2

It is part of General Relativity that if you are in a (small) closed box, you cannot tell the difference between acceleration and a gravitational field. I suppose you could argue that you would explain Earth's gravity to the occupants of the biosphere as a 1g acceleration away from the Earth for 50 years, a slow swivel of the spacecraft, and then ...

2

Can they see the stars? If not then motion is undetectable in a closed environment as it would constitute an inertial frame. But even if they could see the "stars" presumably these would be generated by some form of display technology and behave consistently with the supposed mission profile. However acceleration is detectable, it would manifest as a ...

2

For certain methods of propulsion, you need a medium. In space, you can use a medium that includes cosmic wind in order to drive something like a solar sail. In that case, the energy of particles is important even if they are sparse. However, often you use a rocket engine in space and it doesn't matter what you are moving through. Not to mention that ...

2

Define "current". If one particle makes a current, there are lots of particles that hit the Earth at energies much more than 0.98c, most famously the "Oh my god particle" If you have many particles travelling at these speeds you don't have a river, more a beam, or a jet or particles. These are produced by active accretion disks around black holes. In ...

2

Here's a Wikipedia page discussing various theoretical methods of propulsion. It has some very interesting ideas. The one that piqued my interest was the Alcubierre drive. For all intents and purposes it is a warp drive - well, as close as science can get to the fictional engine of The Enterprise anyway. It has been nicknamed the warp drive, I believe, by ...

2

It's not that much about the speed, but about the orbital eccentricity. Wikipedia gives a good explanation: Based on observations spanning 34 days, ʻOumuamua's orbital eccentricity is 1.20, the highest ever observed. An eccentricity exceeding 1.0 means an object exceeds the Sun's escape velocity, is not bound to the Solar System and may escape to ...

1

You can never reach the speed of light but can get very close to it. Thus, when you travel with, say, 99.99% speed of light it will take you a little more than 31 years to reach the star 31 light years away. This is, however, the time it takes seen from earth. In the spaceship, the time taken will be dilated by $$\gamma ={1\over \sqrt {1-{v^2\over c^2}}}$$ ...

1

Yes it's theoretical, but on some levels, estimates can be calculated. (probably better for space-ex than here), but it's a fun design to think about. The basic design, the ship generates a magnetic field and catches atoms in space as it moves. I've read that the "catch" might be about a square mile in area, so you can calculate how much hydrogen and ...

1

Related: https://physics.stackexchange.com/questions/26326/how-dense-are-nebulae Let's compare nebulae to the air density where the ISS orbits, at 400 000 meters. According to Wikipedia, air pressure at a given altitude is given by the equation $$p = p_0 \left(1 - \frac{Lh}{T_0} \right)^\frac{gM}{RL}$$ or $101.325\left(1 - \frac{0.0065×400000}{288.15}\... 1 In the first example, you certainly could use the calculation of special relativity to measure the difference in the time shown on a clock which was making the high speed journey and one which was at rest. The details may make the calculation trickier, but we can use the flat minowsky space of the clock at rest to do the calculation, so it is relatively ... 1 You can determine the 3D position for a star,$p$, by using the distance from Earth,$R$, as well as the right ascension,$\Omega$, and declination,$\delta$, within the following formula.$p = R \begin{bmatrix} \cos \Omega \cos \delta \\ \sin \Omega \cos \delta \\ \sin \delta \\ \end{bmatrix}\$ Note this will yield positions within the Earth-centered ...

1

I don't know about a spaceship, but the XKCD guy wrote an interesting article about what would happen if Earth was hit by a solid asteroid, travelling at various different speeds: what-if question: Diamond The ship would be a lot smaller than an asteroid, so I think the damage would be a lesser version of these descriptions. (The most extreme case ...

1

For small values of practical an interstellar Orion craft could achieve ~3.3% c (~133 years to Alpha Centauri, one way with no deceleration at the end of the trip)). Which is in principle within reach of present technology if we chose to pursue it. But cost and aversion to nuclear technology on such an extravagant scale make it unlikely that we will see ...

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