17
   

The Fermi Paradox

 
 
oralloy
 
  -1  
Reply Sun 10 Dec, 2017 08:07 pm
@gungasnake,
gungasnake wrote:
There is one possible shot at ftl travel and that would involve Biefeld/Brown propulsion. Question is, is it real??

Good to see you're still posting.

I doubt that any FTL travel can ever be done, regardless of how advanced the technology is.
0 Replies
 
oralloy
 
  -1  
Reply Sun 10 Dec, 2017 08:29 pm
@farmerman,
farmerman wrote:
we use interferometry which links several radioscopes together and "knits the signals by dismissing any spurious signals and reinforcing the main ones sort of in a 3 d fashion." But it usually only works with a signal that allows enough parallax. I suppose if we hd more radioscopes in space aimed at a segment of the galaxy we would have better distance discrimination and better signal enhancement.

I did some web searching on how far out our signals could reach, and not surprisingly got some contradictory information.

This says that our TV carrier waves can only be detected out to a third of a light year:
http://www.faqs.org/faqs/astronomy/faq/part6/section-12.html

This claims 16 or even 50 light years:
http://www.quora.com/Could-Earth-pick-up-signals-from-a-hypothetical-clone-of-Earth-12-lightyears-away/answer/Michael-Busch-4

It appears that the first signals with the frequency and power to penetrate through the upper atmosphere were the broadcasts of the Nazi Olympics. Earlier radio transmissions were short wave and bounced off the ionosphere. Way to make a good first impression on the aliens.

Despite the limitations of our TV range, our early warning radars (both NATO and USSR) looking out for nuclear attack have been beaming strong directional signals into space that will reach for quite a long distance. These don't carry any information in the signals and if any of them are detected at stellar distances it will just be a single fleeting pulse, so an intercepted radar pulse may or may not be interpreted as an intelligent transmission, but they are going to reach considerably farther than our TV and radio transmissions.
farmerman
 
  1  
Reply Mon 11 Dec, 2017 04:02 am
@oralloy,
I read the Quora article and it looks like its a wavelength and frequency issue. I see that radars can possible be detected at a 100K lightyears while normal radio , much shorter.

An assignment for one of our students is to do a frequency v distance graph at normal reception and then another at enhanced (interferometry with aperture control ) reception
Krumple
 
  1  
Reply Mon 11 Dec, 2017 05:31 pm
@oralloy,
oralloy wrote:

We would send unmanned probes to do the early exploration.


Even with this. It is still impractical. If it takes thousands of years to send a probe and that probe returns information limited by the speed of light. You still need to wait for the probe to arrive which can take thousands of years. This might mean hundreds of generations have to wait before the investment your ancestors put together.

Imagine if people from 1017 sent out a space probe to alpha centari. or further and it took 1000 years before we got back any data. We had to wait 1000 years before there was any pay off. The people who put together the project are all dead. Even their grand children are dead. No one related to the project are living.

Then you want to tell me that we get some "good" data that we decide to construct a ship in space and put on board a few hundred people who are going to "live" on this ship for another 1000 years to go there?

No it's absolutely silly. Pure silliness. Completely impractical. Unrealistic.
oralloy
 
  -1  
Reply Mon 11 Dec, 2017 06:43 pm
@farmerman,
farmerman wrote:
I see that radars can possible be detected at a 100K lightyears

That's not good. I hope we don't get noticed by something hostile.
0 Replies
 
oralloy
 
  -1  
Reply Mon 11 Dec, 2017 06:44 pm
@Krumple,
Krumple wrote:
Even with this. It is still impractical. If it takes thousands of years to send a probe and that probe returns information limited by the speed of light. You still need to wait for the probe to arrive which can take thousands of years. This might mean hundreds of generations have to wait before the investment your ancestors put together.

Imagine if people from 1017 sent out a space probe to alpha centari. or further and it took 1000 years before we got back any data. We had to wait 1000 years before there was any pay off. The people who put together the project are all dead. Even their grand children are dead. No one related to the project are living.

The nearby stars wouldn't take so long if we sent the probe at high speed. But even with really long trips, so what? We might not live to see the results, but future generations will benefit. I don't see why a long duration makes unmanned probes impractical. After we send them out, they won't take any further effort from us until it comes time to receive the data.


Krumple wrote:
Then you want to tell me that we get some "good" data that we decide to construct a ship in space and put on board a few hundred people who are going to "live" on this ship for another 1000 years to go there?

No it's absolutely silly. Pure silliness. Completely impractical. Unrealistic.

I am unsure of the size of a one-way colony ship that we might construct thousands of years in the future, but the journey would not take very long for the travelers at all. Don't forget about time dilation.
Krumple
 
  1  
Reply Mon 11 Dec, 2017 07:06 pm
@oralloy,
oralloy,

You are completely ignoring the practicality of it. You can't instantly accelerate to the speed of light. That amount of inertia would make you a pile of goo on the back wall of the ship.

You would need to accelerate around ONE g, or one earth gravity unit. Sure you could accelerate at 2 G if you wanted but imagine you would be under the effects of twice earth's gravity for dozens of years.

HOW long does it take to accelerate at 1 g to reach 99% the speed of light? If you try to accelerate faster it's going to impact the people inside.

Not ONLY acceleration needs to be taken into consideration but slowing down needs to be considered too! So when you are half way to your destination you need to turn the ship 180 degrees and slow down at 1 g for the rest of the trip.

This doesn't even consider the fuel it would require to accelerate and decelerate a ship at 1 g, for ten years? Twenty years? a hundred years?

So considering acceleration and deceleration, this means that for a HUGE majority of the trip you are not traveling any where near the speed of light to take advantage of time dilation.

Once again, you are being silly. Not considering the factors involved. IT is 100% impractical.
oralloy
 
  -1  
Reply Mon 11 Dec, 2017 07:50 pm
@Krumple,
Krumple wrote:
HOW long does it take to accelerate at 1 g to reach 99% the speed of light?

Approximately one year. Slightly less actually, but close enough for purposes of this thread, as we aren't computing a trajectory for an actual voyage.


Krumple wrote:
Not ONLY acceleration needs to be taken into consideration but slowing down needs to be considered too! So when you are half way to your destination you need to turn the ship 180 degrees and slow down at 1 g for the rest of the trip.

People on board a ship accelerating at 1 g for the entire first half of the journey and decelerating at 1 g for the entire second half of the journey will experience the passage of 24 years on a trip that traverses the entire diameter of the Milky Way galaxy.


Krumple wrote:
This doesn't even consider the fuel it would require to accelerate and decelerate a ship at 1 g, for ten years?

We'll have thousands of years before unmanned probes (that we haven't even sent yet) start returning data from other stars about potential colony sites. That's plenty of time for propulsion technology to improve.
Krumple
 
  1  
Reply Mon 11 Dec, 2017 08:44 pm
@oralloy,
oralloy wrote:
We'll have thousands of years before unmanned probes (that we haven't even sent yet) start returning data from other stars about potential colony sites. That's plenty of time for propulsion technology to improve.


I think we wouldn't have the technology in 10,000 years of human development. Sure you can theorize all you want over how ship engines would work. But you can't bypass the laws of physics or thermodynamics.

You would either need to collect the fuel on the way to the destination which is possible but probably highly unlikely. By scooping up free roaming hydrogen atoms in space. But you would need an enormous object to be able to scoop up enough hydrogen to make it worth it.

You can't get around mass. The more mass the ship has the more energy required to move it. So if you try to take the fuel with you, on the entire journey then the acceleration is impacted by the increase in mass for carrying the fuel. Not to mention space or the conversion of the mass. Maybe if you had a nuclear generator on board you can simply convert small amounts of plutonium into electric power and use it as fuel. But you still need other equipment to handle the process.

Sure there are theoretical fuels that are "safer" than nuclear but you still need equipment and equipment increases the mass. So you can't get around having free energy to push a large craft without losing something in the process. Just saying you can, is a violation of thermodynamics. NO amount of technology is going to bypass that.

probably 60% of the trip is WAY under light speed. Due to acceleration and deceleration. So YOU cant take advantage of any time dilation at all. So you are wrong about 24 years to travel the circumference of the galaxy. You are completely ignoring the time to accelerate and decelerate.

One year (365 days) to accelerate from 0 to 186,000 miles/second at 9.8 m/s ?

Did you fail math class?
Krumple
 
  1  
Reply Mon 11 Dec, 2017 08:54 pm
@oralloy,
oralloy wrote:

Krumple wrote:
HOW long does it take to accelerate at 1 g to reach 99% the speed of light?

Approximately one year. Slightly less actually, but close enough for purposes of this thread, as we aren't computing a trajectory for an actual voyage.


By my math it would take over 9 years to accelerate from 0 to 186,000 miles per second (c). at 1 g (9.8m/s2)
oralloy
 
  -1  
Reply Mon 11 Dec, 2017 10:37 pm
@Krumple,
Krumple wrote:
probably 60% of the trip is WAY under light speed. Due to acceleration and deceleration. So YOU cant take advantage of any time dilation at all. So you are wrong about 24 years to travel the circumference of the galaxy. You are completely ignoring the time to accelerate and decelerate.

The figure of 24 years to travel the diameter of the galaxy includes continuous 1 g acceleration from a stop and then continuous 1 g deceleration to a stop.


Krumple wrote:
One year (365 days) to accelerate from 0 to 186,000 miles/second at 9.8 m/s ?
Did you fail math class?

No, but I was lazy and Googled instead of doing the figures myself. There seems to be a pretty sound consensus among those who did do the figures. I merely quoted that consensus.
0 Replies
 
oralloy
 
  -1  
Reply Mon 11 Dec, 2017 10:38 pm
@Krumple,
Krumple wrote:
By my math it would take over 9 years to accelerate from 0 to 186,000 miles per second (c). at 1 g (9.8m/s2)

Even if that is true, that would not be a barrier to interstellar voyages.
oralloy
 
  -1  
Reply Mon 11 Dec, 2017 10:41 pm
@Krumple,
Krumple wrote:
You can't get around mass. The more mass the ship has the more energy required to move it. So if you try to take the fuel with you, on the entire journey then the acceleration is impacted by the increase in mass for carrying the fuel. Not to mention space or the conversion of the mass. Maybe if you had a nuclear generator on board you can simply convert small amounts of plutonium into electric power and use it as fuel. But you still need other equipment to handle the process.

If I were going to imagine how it would be done, I'd have them use a nuclear reactor to provide energy for an ion drive powerful enough to provide 1 g acceleration.

I have not done any calculations as to what sort of mass would be required for a few years of 1 g acceleration from an ion drive.
Krumple
 
  1  
Reply Mon 11 Dec, 2017 11:24 pm
@oralloy,
oralloy wrote:

Krumple wrote:
By my math it would take over 9 years to accelerate from 0 to 186,000 miles per second (c). at 1 g (9.8m/s2)

Even if that is true, that would not be a barrier to interstellar voyages.


Yes it would because you are only considering one aspect. acceleration. You still need to slow down. So you can only travel up to the point of 50% the distance to your destination then you need to slow down.

If the destination was < 18 years you would only be near the speed of light about 10% of the trip. So nearly 90% of the trip you can't take time dilation into any kind of effect.
Krumple
 
  1  
Reply Mon 11 Dec, 2017 11:34 pm
@oralloy,
oralloy wrote:

Krumple wrote:
You can't get around mass. The more mass the ship has the more energy required to move it. So if you try to take the fuel with you, on the entire journey then the acceleration is impacted by the increase in mass for carrying the fuel. Not to mention space or the conversion of the mass. Maybe if you had a nuclear generator on board you can simply convert small amounts of plutonium into electric power and use it as fuel. But you still need other equipment to handle the process.

If I were going to imagine how it would be done, I'd have them use a nuclear reactor to provide energy for an ion drive powerful enough to provide 1 g acceleration.

I have not done any calculations as to what sort of mass would be required for a few years of 1 g acceleration from an ion drive.


You still have to consider the equipment involved in the conversion of the fissionable material into electrical energy. Currently we use water to be converted into steam to turn a turbine connected to a coil of wire. But you also need water to cool the reactor. The whole fission process of nuclear reactor needs to be cooled. Sure space is cold but you would need to circulate the water from within the reactor core to a place that can cool it down and reinsert it back into the core.

This doesn't even take into consideration the shielding required to keep the passengers safe from the radiation of the water being pumped through the system and the reactor itself.

The fuel rods also don't last for ever. They need to be replaced. This requires a method of extraction and exchange for new rods. And safely jettisoning the spent fuel rods. The system needs to be contained to prevent radiation exposure. All this containment requires materials for shielding and mechanical devices to move the materials.

You would also want back up systems too in case there is a failure of one of its systems. It wouldn't be good to plan a 20 year journey and five years in the system fails. So this requires even more materials to construct a back up system.

Oh by the way ion drives are extremely weak. They don't provide very much mass to thrust ratio. NASA only considers them viable for extremely small satellites. Because their scaling factor has a very small zero sum return ratio. Meaning over a certain size or total mass they can't produce enough thrust to even move the engine itself, let alone a ship attached to that engine.
Setanta
 
  2  
Reply Tue 12 Dec, 2017 12:11 am
The statement by Brian Cox about technological civilizations in our galaxy could be seen as a variant on the Fermi paradox. Professor Cox raised a storm of existential angst when he stated that he believes that ours is the only technological civilization in this galaxy. The storm arose from the typical idiocy of the press, the overwhelming majority of whom reported, erroneously, that he had said we were the only technological civilization in the universe.

Cox stated that it would take humanity about ten million years to colonize this galaxy, had we the means, and that therefore, he believes we are alone, as a technological civilization, in this galaxy. Essentially, it is the same as Fermi's question: "Where are they?" But Cox provided a much more logical basis than Fermi did, and Fermi carelessly referred to the entire universe.

My own take on this has been conditioned by the evidence that we have been getting from orbital telescopes, such as Kepler, which looks for so-called exo-planets. In the process, and from the missions of other orbiting telescopes, it has become apparent the the great majority of stellar systems are binary or trinary, and in fact, astronomers now believe that most stellar systems are trinary. Star systems of four, five, six and even seven stars have been found. I suggest that this means that planets in such systems are exposed to high amounts of stellar radiation, as well as exposure to extremes of gravitational flux (see Guass' law). It is now obvious that the early history of our stellar system, which we call the solar system, was like a shooting gallery, or a vast pinball game with "asteroids" and planetesimals careering around and leading to the sorts of collisions which astronomers now believe are responsible for the axial tilts of many of the planets--even our star, Sol, has an axial tilt of about seven degrees; that of Earth is twenty-three and a half degrees, and that of Mars, twenty-five degrees. Although most bodies observed in the solar system move from west to east (left to right, if one could observe them from a position equivalent to the plane of the ecliptic), there is abundant evidence of objects moving in the opposite direction, and many moving along very eccentric paths. There is an impact crater on Mras, called the Hellas Planitia, which shows that the impacting object, a planetesimal about 125 miles in diameter, came in low and from the east, rather than from the west. (Both the moons of Mars--Phobos and Deimos--are apparent captures, and rise in the west and set in the east. Phobos is very low--about 3300 miles above Mars--and moves very fast. Were you on the surface of Mars, it would cross your visual horizons in less that five hours.)

Given that the more we know about our own stellar system, which increasingly reveals a system without the regularity and symmetry which early astronomers believed in, it occurs to me that in multi-star systems, the gravitational influence of the stars dancing around one another, would make the planets in the systems highly unstable. I subscribe without hesitation to Cox's view that the rise of humans and the creation of a technological civilization is entirely fortuitous. I go farther and doubt that there would be very many such "happy accidents" in any galaxy. I don't think we're necessarily alone in the universe, but I seriously doubt that we'll ever encounter any technological neighbors.
0 Replies
 
oralloy
 
  -1  
Reply Tue 12 Dec, 2017 04:55 am
@Krumple,
Krumple wrote:
You still have to consider the equipment involved in the conversion of the fissionable material into electrical energy. Currently we use water to be converted into steam to turn a turbine connected to a coil of wire. But you also need water to cool the reactor. The whole fission process of nuclear reactor needs to be cooled. Sure space is cold but you would need to circulate the water from within the reactor core to a place that can cool it down and reinsert it back into the core.

This doesn't even take into consideration the shielding required to keep the passengers safe from the radiation of the water being pumped through the system and the reactor itself.

The fuel rods also don't last for ever. They need to be replaced. This requires a method of extraction and exchange for new rods. And safely jettisoning the spent fuel rods. The system needs to be contained to prevent radiation exposure. All this containment requires materials for shielding and mechanical devices to move the materials.

You would also want back up systems too in case there is a failure of one of its systems. It wouldn't be good to plan a 20 year journey and five years in the system fails. So this requires even more materials to construct a back up system.

Those are engineering problems, not insurmountable barriers. Given thousands of years more time for our technology to advance, we should be able to manage something.


Krumple wrote:
Oh by the way ion drives are extremely weak. They don't provide very much mass to thrust ratio. NASA only considers them viable for extremely small satellites. Because their scaling factor has a very small zero sum return ratio. Meaning over a certain size or total mass they can't produce enough thrust to even move the engine itself, let alone a ship attached to that engine.

If it turns out that they cannot be scaled up to the level necessary to provide 1 g acceleration/deceleration, then some other technology will be used instead.
0 Replies
 
oralloy
 
  -1  
Reply Tue 12 Dec, 2017 04:56 am
@Krumple,
Krumple wrote:
Yes it would because you are only considering one aspect. acceleration. You still need to slow down.

No, I am considering both aspects.


Krumple wrote:
So you can only travel up to the point of 50% the distance to your destination then you need to slow down.

If the destination was < 18 years you would only be near the speed of light about 10% of the trip. So nearly 90% of the trip you can't take time dilation into any kind of effect.

An 18 year trip isn't an insurmountable barrier for a large team of volunteer colonists making a one-way journey.

And I suspect that the people who say that it only takes one year to hit light speed are correct. I didn't bother figuring it out for myself, but when I Googled I saw the same figures confidently stated by a number of different sources.

But either way, not an insurmountable length of time.
0 Replies
 
Brandon9000
 
  0  
Reply Tue 12 Dec, 2017 05:53 am
The speed of light is about 3 x 10^8 m/s, so the time required to get to it at 9.8 m/s^2 (1G) is 3 x 10^8 m/s divided by 9.8 m/s^2 = 30,612,245 seconds. Dividing this result by 3600 seconds per hour gives 8,503 hours. Dividing by 24 hours per day gives 354.3 days.
Olivier5
 
  1  
Reply Fri 15 Dec, 2017 12:50 pm
@Brandon9000,
As you must know, this is correct in Gallilean mechanics but not in Einstein's relativity, which states that it would take infinite energy for any mass to reach C. Assuming an interstellar spaceship could possibly reach 1/2C for a 1/3 of its trip (acceleration time 1/3 of trip length, 1/2C for 1/3, and deceleration for 1/3) , a trip of 10 lightyears would take what, 30 years to complete?
 

 
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