17

Olivier5

2
Fri 15 Dec, 2017 01:00 pm
Meanwhile:

No Signs of Life Yet on 'Oumuamua'
https://www.space.com/39100-interstellar-object-oumuamua-alien-life-search.html

0 Replies

oralloy

0
Fri 15 Dec, 2017 05:04 pm
@Olivier5,
Olivier5 wrote:
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.

Right, but once you get increases in energy requirements, you also change the passage of time for the travelers. So the figures are a good way to show that at 1 g acceleration you can achieve noteworthy time effects after just one year of acceleration.

Olivier5 wrote:
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?

That sounds reasonable although I didn't do any calculations.

But if a ship accelerates at 1 g for the entire first half of the trip, and then decelerates at 1 g for the entire second half of the trip, it will achieve considerably faster speeds than that.
Olivier5

1
Sat 16 Dec, 2017 01:18 pm
@oralloy,
Right. I suppose the issue is the mass of fuel one would need for multi-year engine burns.
oralloy

0
Sat 16 Dec, 2017 04:51 pm
@Olivier5,
Olivier5 wrote:
Right. I suppose the issue is the mass of fuel one would need for multi-year engine burns.

That will be a major issue. We will need engines with an efficiency and energy output that we can't even come close to producing today.

But no colonists are going to set off on a one way trip to another star system unless unmanned probes first tell us that it is worth settling there. So we'll have thousands and thousands of years before anyone has to worry about actually building an interstellar colony ship. Hopefully by then human technology will be more advanced.
Olivier5

1
Mon 18 Dec, 2017 06:58 am
@oralloy,
Quote:
So we'll have thousands and thousands of years before anyone has to worry about actually building an interstellar colony ship.

Indeed, at least assuming civilisation as we know it doesn't crumble under the pressure of climate change. I.e. assuming we still have a technologically able human civilisation thousands of years from now.
farmerman

1
Mon 18 Dec, 2017 09:29 am
@Olivier5,
what about the EM drive?? DOnt tell me that its dead again?? It seemed like such an easy ide to use deep space ion flux to power an engine using microwaves. Itd be fuel free and it could be built in orbit like a small city. When done right it could reach 50% (c).

I hope that wasnt sci fi cause itd be one of the first of the laws of physics wed be "bending a bit"
Olivier5

2
Mon 18 Dec, 2017 10:00 am
@farmerman,
Not sure the EM engine was ever alive to start with. It's just an idea at the moment, an idea that seems illogical.
farmerman

1
Mon 18 Dec, 2017 10:13 am
@Olivier5,
it did seem to contradict Newtons third law but Id seen a mathematical analyses at a TED talk and its real enough. There are a number of separate space agencies working on it (Russia and China are cooperating as is UK, and the US).
Fil Albuquerque

1
Mon 18 Dec, 2017 11:34 am
@Olivier5,
Here is a relatively recent take on it:

Olivier5

1
Mon 18 Dec, 2017 11:40 am
@farmerman,
Call me a doubter on this one, especially as it applies to moving dozens of tons of stuff and people across dozens of lightyears... I think you would need a prohibitively large EM drive to achieve that. Even if the thing was ever to work on a small scale.
0 Replies

Krumple

1
Mon 18 Dec, 2017 02:27 pm
@oralloy,
oralloy wrote:
Right, but once you get increases in energy requirements, you also change the passage of time for the travelers. So the figures are a good way to show that at 1 g acceleration you can achieve noteworthy time effects after just one year of acceleration.

There is another factor too, although small but still a factor. Not to be annoying here but bringing up how engines work.

Lets imagine that fuel is not an issue here. You have plenty of fuel.

The way an engine works is it is essentially spraying out matter out the back and this causes the ship to be "pushed" in the opposite direction. Simple, you probably already know that. Obvious right?

Well the matter being sprayed out needs to actually travel faster than the resultant thrust. Did that sentence make any sense? The "exhaust" coming out of the engine moves faster than the resulting thrust experienced by the ship. Its not perfectly equal. You get some loss because the exhaust isn't limited by mass where as the ship is limited by mass. So the exhaust moves faster. Hopefully that makes sense.

Now, if a ship needed one last drop of thrust to reach C then it also means the exhaust coming out of the engine would have to move faster than C. But it can't. The exhaust can not move faster than C to allow the ship to obtain that last little bit of thrust.

So even if you could technically make matter move at the speed of light. We would be limited by the way engines work.
farmerman

1
Mon 18 Dec, 2017 02:40 pm
@Krumple,
you dont have to have a v >(c). You can settl for an infinite mass
Krumple

1
Mon 18 Dec, 2017 03:04 pm
@farmerman,
farmerman wrote:

you dont have to have a v >(c). You can settl for an infinite mass

I have never accepted this idea that if you have mass then it goes to infinity at C.

I am 99% certain that we have missed something here. Any time you invoke the infinity, in my opinion you have made a mistake more than likely.

I know, i know that is is widely accepted that if you have mass then near C or at C you gain infinite mass. I know, so many just accept it as a fact. I don't. Call me stupid or an idiot, but I don't accept it. I know the math supposedly proves that mass goes to infinity. My point is, there is a factor that is missing. It is missing because we can't see it yet.
Olivier5

1
Mon 18 Dec, 2017 04:08 pm
@Fil Albuquerque,
There's an excellent comparison in this video: an EM drive is like trying to move a car by pushing the windshield from the inside of the car.
Olivier5

1
Mon 18 Dec, 2017 04:09 pm
@Krumple,
The math has been confirmed in particle accelerators.
Krumple

1
Mon 18 Dec, 2017 04:24 pm
@Olivier5,
Olivier5 wrote:

There's an excellent comparison in this video: an EM drive is like trying to move a car by pushing the windshield from the inside of the car.

Most people don't understand why this is a problem.

A major factor in video creation on "hyper" ideas is that even if the whole thing is nonsense, it generates money on the millions of views it gets. So then the internet is littered with garbage ideas because they make viewership money from ads.

When all this "garbage" gets put out, there is nothing coming along to clean it up. It stays out in the public domain. Sure people come by and debunk it but there is no money in debunking these silly ideas. And a huge majority of people are not interested in hearing why an idea just wont work or is silly. So the internet fills up with garbage and there is very little cleaning being done.
farmerman

1
Mon 18 Dec, 2017 04:33 pm
@Krumple,
no thats not the case. There is a change of phase state with the generation of focused microwaves and they exit the "nozzle" they do it at something likeat 1/3 less energy, so the "action reaction" is somewhere about 2/3 of the E budget from generation of the microwaves. With a very very large array(Think Death Star), it could most efficiently move in space like a small country

The concept, as I found out, is still above my pay grade because of the "phase rule" rules invoked . I too was an initial disbeliever but at a Ted talk, they reviewed a number of "ion propulsion " or similar "fuel-free" drives and this ws given serious talk by serious JPL scientists.
(Doesnt mean it will work but theres a lot of geometry , phase rule, and Snells Law **** involved)
0 Replies

Krumple

1
Mon 18 Dec, 2017 04:39 pm
@Olivier5,
Olivier5 wrote:

The math has been confirmed in particle accelerators.

How? Where is the example that a particle with mass obtained infinite mass once it reached C?

I think what you are referring to is a person regurgitates this as a limitation. They don't achieve it because it is already believed that you can't do it. If you already believe it can't be done, why would you try to do it? So they just say, it wasn't done because it can't be done. No actual experiment was carried out because it's already accepted that it can't be done.
farmerman

1
Mon 18 Dec, 2017 04:45 pm
@Krumple,
Quote:
you dont have to have a v >(c). You can settl for an infinite mass
I thought I posted that e need an irony button. I was kidding about the mass thing (unless we can keep it at 80% c).
However, EM drives, Im not sure we here can give it a fair hearing by cross posting Wiki sites.

Several JPL scientists took prt in a discussion that , in review, were convinced that, with several major requirements (read: very large arrays/ Orbital construction and provisioning) It could work at sometime in our future.
Thats all the dog I hve in the fight right now, although we use phase rule and phase change for extrcting energy from molten salts I think such thermodynamics COULD be used in generating Photons and microwaves
0 Replies

Olivier5

1
Tue 19 Dec, 2017 02:10 am
@Krumple,
By accelerating heavy particles close to the speed of light, they can see that the energy required rises more and more as they get ever closer to C... Very simple.
0 Replies

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