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HellBlazer
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PostPosted: Sun Nov 06, 2016 7:30 pm 
 

Construction of the James Webb Space Telescope is finally completed: http://www.popsci.com/sites/popsci.com/ ... 1&fc=50,50

Now, two years of testing before launch in October 2018.

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droneriot
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PostPosted: Sun Nov 06, 2016 7:40 pm 
 

Well, when New Horizons was launched I thought it'll be FOREVER till it arrives, yet it happened, time passed quickly. When I first heard of JWST I thought the same, and I think the last two years will pass quickly, too.
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droneriot
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PostPosted: Tue Nov 08, 2016 12:52 pm 
 

Does anyone know if Elon Musk and by extension his companies profit from Hyperloop One's ventures since he's the one who put it forward? Today I just read about the unveiling for the first hyperloop system in - where else - the United Arab Emirates (link), and I was wondering if this (or the eventual completion of the Tesla gigafactory) would benefit SpaceX, the most important company at the moment in my opinion (besides asteroid mining companies.)
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HellBlazer
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PostPosted: Wed Nov 09, 2016 6:46 pm 
 

droneriot wrote:
Does anyone know if Elon Musk and by extension his companies profit from Hyperloop One's ventures since he's the one who put it forward? Today I just read about the unveiling for the first hyperloop system in - where else - the United Arab Emirates (link), and I was wondering if this (or the eventual completion of the Tesla gigafactory) would benefit SpaceX, the most important company at the moment in my opinion (besides asteroid mining companies.)


As I understand it, Musk put the hyperloop concept out there for anyone to use and develop, and does not stand to financially profit from it. He is interested in putting the technology to use on Mars though, so it could help SpaceX in that way.

As for Tesla and the Gigafactory, they're not related to SpaceX at all (unless SpaceX needs batteries I guess, in which case Tesla could be a supplier). Though, if Tesla becomes very successful, Musk himself makes more money, so I suppose he could decide to re-invest some of that cash into SpaceX if he feels a need to.

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zingote
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Joined: Fri Dec 11, 2009 8:57 pm
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PostPosted: Sat Nov 12, 2016 11:48 pm 
 

I've got a few questions:

1. A recent study suggests that there are 10 times more galaxies in the observable universe than previously thought (up to 2 trillion instead of 200 billion). Is that an estimate of the current number or of those that have ever existed?

2. What's the difference between the "Big Rip" and "Big Freeze" scenario? My understanding is that both of them involve an expansion of the universe until matter rips itself apart. How does that affect a potential Multiverse? Can another Big Bang occur afterwards?

3. What would happen if a ship was passing through a nebula?

4. The term "spacetime" is often used, which involves 4 dimensions (3 spacial ones and time). If time is a dimension does it mean that its a variable? How can time be a variable when it progresses in a linear fashion? The other three will change according to movement.

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Earthcubed
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PostPosted: Sun Nov 13, 2016 4:50 pm 
 

1. It's an estimate of those galaxies which can currently be observed through a telescope. Many of these are hundreds of millions or several billion light-years away, which means we are seeing them as they were hundreds of millions of years ago or billions of years ago. Over time, many galaxies merge with each other, resulting in fewer galaxies overall. Therefore, the actual number of galaxies currently in existence is probably lower, since many of the furthest galaxies have likely collided and merged in the time it took for their light to reach us.

2. There's nothing in common between a rip and a freeze. The freeze scenario is that the universe keeps expanding indefinitely until the overall average heat of any single place in the cosmos is too cold to support life or any energetic processes---this is because the distance between stars (heat sources) grows too large, and also because the rate of star creation slows.

We know that the rate at which space expands is continually increasing. In the hypothetical Big Rip scenario, eventually the expansion rate of space exceeds not only the strength of gravity but also the strength of magnetism, the strong nuclear force, and the weak nuclear force. Essentially, the space within atoms expands faster than the forces holding them together---every atom "rips" apart.

Either of those scenarios should have no effect on any potential multiverse...most theories of multiple universes don't really allow for much interaction between universes. There are some theories which allow for nearby universes to bump into each other, but I don't think a Big Rip or Big Freeze changes that.

3. There would be more visible dust and general space debris than there would be when passing through our solar system, and possibly a higher amount of asteroids and comets as well...those last two things depend on how many comets/asteroids are just aimlessly floating in space versus orbiting stars. But the density of a nebula is still low enough that just about anything humans could possibly build would probably still be small enough to safely pass through.

4. This is well beyond what my math-retardant brain can answer. :)
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droneriot
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PostPosted: Sun Nov 13, 2016 5:26 pm 
 

Earthcubed wrote:
We know that the rate at which space expands is continually increasing.

We have a theory that not everybody agrees on, it is one of the more accepted theories with a good amount of evidence, but still firmly short of "we know."
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zingote
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PostPosted: Mon Nov 14, 2016 12:15 am 
 

droneriot wrote:
Earthcubed wrote:
We know that the rate at which space expands is continually increasing.

We have a theory that not everybody agrees on, it is one of the more accepted theories with a good amount of evidence, but still firmly short of "we know."


That's the reason why i excluded the "Big Crunch" scenario in my question. However, if the universe starts contracting, then it may still be possible.

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Dudemanguy
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PostPosted: Mon Nov 14, 2016 4:20 pm 
 

zingote wrote:
4. The term "spacetime" is often used, which involves 4 dimensions (3 spacial ones and time). If time is a dimension does it mean that its a variable? How can time be a variable when it progresses in a linear fashion? The other three will change according to movement.


Warning: Incoming physics post.

Time has always been a variable. It's just that before relativity; it was assumed that time was independent and homogeneous everywhere (since you know, that's how we all experience it). Under Newtonian law (i.e. without taking relativity into account), yes time is merely a scalar quantity that progresses linearly. But in reality, time does not progress linearly for all reference frames.

One curious thing that physicists discovered over 100 years ago was that the speed of light (in a vacuum) was a constant. That is, no matter the reference frame, the speed was always the same. To help put this in perspective, think of driving perfectly alongside a car down the highway. Relative to the ground, your speed is say 100 km/h. But your speed relative to the other car is 0. This is what physicists mean by "reference frame." It's expected that measurements of a certain event can differ if you use different reference frames. As another example, the earth rotates at whopping 460 m/s. But we don't feel it because all of us rotate with it at the exact same speed. So in most cases, the earth's rotation is completely irrelevant to many measurements that people make (not all of them though).

So back to the point, the speed of light was observed to be a single, constant value no matter where you measured it. This was surprising because at the time people expected light to propagate as a wave through a medium (like sound). Thus it stands to reason that if you measured the propagation from different angles, you would have different results right? If you were moving towards an incoming light ray, you would expect the speed to be greater than if you were moving with it (think of driving on a highway). However, this in fact does not happen. Light travels at the exact same speed in both cases. The conclusion drawn is that no such medium exists and light (aka electromagnetic waves) travel without needing any medium.

So now we have a contradiction arising in Newtonian physics. Newton wasn't wrong; all of his formulations hold perfectly fine for lower speeds. But we can clearly see a breakdown when objects approach the speed of light. For another example, consider a space ship traveling at 0.7c in a vacuum (70% of the speed of light). While it travels at that speed, the spaceship emits a pulse of light. Under Newtonian physics, the speed of light relative to the vacuum would be 1.7c (0.7c + c). However, this obviously cannot be correct as everyone knows nothing moves faster than the speed of light. There are other examples of how Newtonian physics breaks down at higher speeds (energy is another example), but that's just a simple one.

This meant that the laws of physics needed to be reformulated to accommodate the observations we see at high speeds and they need to approximate to Newton's laws at low speeds. In order for the speed of light to be a constant, that means that both space and time are nonlinear (because velocity is a function of distance and time, dr/dt). This is where things get hairy. When you travel close to c, time must slow down (i.e. time dilation). Why? Because speed is the constant not time. Similarly, another phenomenon called length contraction exists. That is, objects moving at high speeds will contract in length. Both of these strange occurrences are cold, hard confirmed truths. The universe is a weird place. When you throw in gravity, you get general relativity which is a different mess that's much, much more complicated.

From what we know, there is no way to "turn back" time (i.e. go back in time) like how displacement can simply be undone by putting force in the opposite direction. Of course, in our everyday lives, relativity is not really noticeable since almost none of us deal with speeds close to the speed of light. However, it's important to conceptually grasp that both time and space are relative (hence the name; relativity) quantities that vary depending on the reference frame. There is no universal time or length; that's just not how our universe works.
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zingote
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PostPosted: Mon Nov 14, 2016 9:43 pm 
 

Dudemanguy wrote:
zingote wrote:
4. The term "spacetime" is often used, which involves 4 dimensions (3 spacial ones and time). If time is a dimension does it mean that its a variable? How can time be a variable when it progresses in a linear fashion? The other three will change according to movement.


Warning: Incoming physics post.

Time has always been a variable. It's just that before relativity; it was assumed that time was independent and homogeneous everywhere (since you know, that's how we all experience it). Under Newtonian law (i.e. without taking relativity into account), yes time is merely a scalar quantity that progresses linearly. But in reality, time does not progress linearly for all reference frames.

One curious thing that physicists discovered over 100 years ago was that the speed of light (in a vacuum) was a constant. That is, no matter the reference frame, the speed was always the same. To help put this in perspective, think of driving perfectly alongside a car down the highway. Relative to the ground, your speed is say 100 km/h. But your speed relative to the other car is 0. This is what physicists mean by "reference frame." It's expected that measurements of a certain event can differ if you use different reference frames. As another example, the earth rotates at whopping 460 m/s. But we don't feel it because all of us rotate with it at the exact same speed. So in most cases, the earth's rotation is completely irrelevant to many measurements that people make (not all of them though).

So back to the point, the speed of light was observed to be a single, constant value no matter where you measured it. This was surprising because at the time people expected light to propagate as a wave through a medium (like sound). Thus it stands to reason that if you measured the propagation from different angles, you would have different results right? If you were moving towards an incoming light ray, you would expect the speed to be greater than if you were moving with it (think of driving on a highway). However, this in fact does not happen. Light travels at the exact same speed in both cases. The conclusion drawn is that no such medium exists and light (aka electromagnetic waves) travel without needing any medium.

So now we have a contradiction arising in Newtonian physics. Newton wasn't wrong; all of his formulations hold perfectly fine for lower speeds. But we can clearly see a breakdown when objects approach the speed of light. For another example, consider a space ship traveling at 0.7c in a vacuum (70% of the speed of light). While it travels at that speed, the spaceship emits a pulse of light. Under Newtonian physics, the speed of light relative to the vacuum would be 1.7c (0.7c + c). However, this obviously cannot be correct as everyone knows nothing moves faster than the speed of light. There are other examples of how Newtonian physics breaks down at higher speeds (energy is another example), but that's just a simple one.

This meant that the laws of physics needed to be reformulated to accommodate the observations we see at high speeds and they need to approximate to Newton's laws at low speeds. In order for the speed of light to be a constant, that means that both space and time are nonlinear (because velocity is a function of distance and time, dr/dt). This is where things get hairy. When you travel close to c, time must slow down (i.e. time dilation). Why? Because speed is the constant not time. Similarly, another phenomenon called length contraction exists. That is, objects moving at high speeds will contract in length. Both of these strange occurrences are cold, hard confirmed truths. The universe is a weird place. When you throw in gravity, you get general relativity which is a different mess that's much, much more complicated.

From what we know, there is no way to "turn back" time (i.e. go back in time) like how displacement can simply be undone by putting force in the opposite direction. Of course, in our everyday lives, relativity is not really noticeable since almost none of us deal with speeds close to the speed of light. However, it's important to conceptually grasp that both time and space are relative (hence the name; relativity) quantities that vary depending on the reference frame. There is no universal time or length; that's just not how our universe works.


Thanks for the insightful information.

My notion of time being a variable mostly relates to your last paragraph, thinking of it like an actual time machine. 3D can be defined using the x,y,z coordinates. We can tell people our location on Earth by just using longitude and latitude (x & Y), which will obviously change depending on our location. We can also add topography (z coordinate) to further describe our location if necessary. All of these can therefore be controlled by simple displacement. How do we control time?

I understand the concept of relativity, but even there you can still only move into the future. When we observe the distant universe, we are seeing it as it was in the distant past, a past that no longer exists. All of those distant points are still technically in the present (2016 for lack of a better word).
What about other dimensions? The multiverse theory suggests that there are more than just 4. Is there any way to test out those theories? My understanding of the Multiverse is that its something akin to what was shown in Doctor Strange, in that there is no way to get there my conventional travel, but a portal would be required to interact with it.

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droneriot
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PostPosted: Tue Nov 15, 2016 1:10 pm 
 

Project Blue, a project to launch a small space telescope to directly image planets in the Alpha Centauri system, has launched its fundraising campaign.
http://www.space.com/34724-project-blue ... nding.html
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Dudemanguy
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PostPosted: Wed Nov 16, 2016 11:17 am 
 

zingote wrote:
My notion of time being a variable mostly relates to your last paragraph, thinking of it like an actual time machine. 3D can be defined using the x,y,z coordinates. We can tell people our location on Earth by just using longitude and latitude (x & Y), which will obviously change depending on our location. We can also add topography (z coordinate) to further describe our location if necessary. All of these can therefore be controlled by simple displacement. How do we control time?

I understand the concept of relativity, but even there you can still only move into the future. When we observe the distant universe, we are seeing it as it was in the distant past, a past that no longer exists. All of those distant points are still technically in the present (2016 for lack of a better word).
What about other dimensions? The multiverse theory suggests that there are more than just 4. Is there any way to test out those theories? My understanding of the Multiverse is that its something akin to what was shown in Doctor Strange, in that there is no way to get there my conventional travel, but a portal would be required to interact with it.


Well you can't control time. Theoretically, the best you can do is "go to the future" by moving really fast, but that's it. Looking at distant galaxies and the like is literally looking into the past, but you can't go there. I mean even if you had a magic rocketship that went at light speed, by the time you arrived it would, of course, be far far into the future. Nobody has developed any serious theory that would allow for the possibility of backwards time travel. Unfortunately, a lot of physics is disappointing to sci-fi fans (at least we still have wormholes lol).

Other dimensions? That's yet another clusterfuck, and I really couldn't help you with that. Well theoretically, it's possible that things like quantum entanglement involve interactions with particles from another universe but as to actually verifying and testing those theories, we don't know. And it may be possible that we'll never know. The good news, at least, is that the multiverse theory is actually a "mainstream" theory (i.e. not just whackjobs support it). Out the various QM interpretations out there, I personally consider that one of the "cooler" ones, but I guess we'll just have to wait and see if a particular interpretation ends up being correct in our lifetime.
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zingote
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PostPosted: Thu Nov 17, 2016 3:16 am 
 

Dudemanguy wrote:
zingote wrote:
My notion of time being a variable mostly relates to your last paragraph, thinking of it like an actual time machine. 3D can be defined using the x,y,z coordinates. We can tell people our location on Earth by just using longitude and latitude (x & Y), which will obviously change depending on our location. We can also add topography (z coordinate) to further describe our location if necessary. All of these can therefore be controlled by simple displacement. How do we control time?

I understand the concept of relativity, but even there you can still only move into the future. When we observe the distant universe, we are seeing it as it was in the distant past, a past that no longer exists. All of those distant points are still technically in the present (2016 for lack of a better word).
What about other dimensions? The multiverse theory suggests that there are more than just 4. Is there any way to test out those theories? My understanding of the Multiverse is that its something akin to what was shown in Doctor Strange, in that there is no way to get there my conventional travel, but a portal would be required to interact with it.


Well you can't control time. Theoretically, the best you can do is "go to the future" by moving really fast, but that's it. Looking at distant galaxies and the like is literally looking into the past, but you can't go there. I mean even if you had a magic rocketship that went at light speed, by the time you arrived it would, of course, be far far into the future. Nobody has developed any serious theory that would allow for the possibility of backwards time travel. Unfortunately, a lot of physics is disappointing to sci-fi fans (at least we still have wormholes lol).

Other dimensions? That's yet another clusterfuck, and I really couldn't help you with that. Well theoretically, it's possible that things like quantum entanglement involve interactions with particles from another universe but as to actually verifying and testing those theories, we don't know. And it may be possible that we'll never know. The good news, at least, is that the multiverse theory is actually a "mainstream" theory (i.e. not just whackjobs support it). Out the various QM interpretations out there, I personally consider that one of the "cooler" ones, but I guess we'll just have to wait and see if a particular interpretation ends up being correct in our lifetime.


i wouldn't necessarily say that physics is disappointing. I actually find the universe to be a fascinating place, regardless of how hostile of a place it may be (with the huge number of exoplanet discoveries, we are bound to find something interesting). I'm interested in the planets topographies, not just whether they have aliens or not.

Since you're very knowledgeable, I'd like to ask a few more questions.

1. It's said that the Milky Way contains between 200-400 billion stars (some suggest even a trillion like Andromeda). How can that be if the nearest one to us is 4 ly away and the galaxy is 100 000 ly across? I know that we are in an area with a low number of stars, and there are dense regions like star clusters that have many of them, but the number still seems too big.

2. How do we define the boundaries of a galaxy, if they are not single bodies like stars, planets, moons..., but complex ones made up of many star systems?

3. Are planets/moons able to survive longer than any star since they don't undergo fusion like them? Would they be able to be around until the end of the universe (a Big Rip would tear them apart)?

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Dudemanguy
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PostPosted: Fri Nov 18, 2016 2:26 pm 
 

Well, I suppose it's a matter of perspective. Everyone's been crossing their fingers for Star Trek-like space travel. No luck yet. I guess I just mean that the future hasn't been quite as optimistic as scifi stuff has generally portrayed (where's my REAL hoverboard like from Back to The Future Part II).

1. Regarding the ludicrously high number of stars, it's because galaxies are immensely dense in their centers. As you probably know, virtually all galaxies have a supermassive black hole in the center and they are surrounded by an absurdly large number of stars. I'll pull a quote for you.

Quote:
Within a parsec of the galactic center, the estimated number density of stars is about 10 million stars per cubic parsec. By contrast, the number density of stars in the Sun's neighborhood is a puny 0.2 star per cubic parsec.

http://www.astronomy.ohio-state.edu/~ry ... tes31.html

As you get closer to the center of a galaxy, everything gets much denser (I think it's an exponential function, but I'm not sure).

2. We define galaxies sort of like the same way we define stellar systems. A galaxy is essentially a large collection of stars, planets, nebulas, dark matter, etc. that are gravitationally bound and rotate about a center. In practice, this means the collection of objects that rotate around a supermassive black hole is defined to be a galaxy. Galaxies can take on a variety of shapes (ellipses, spirals, etc) depending on the circumstances in which they were formed. And of course, they can vary dramatically in size as well.

3. Well technically, the vast majority of stars will hang around as a black dwarf (none exist yet because the universe isn't yet old enough for them to have formed from white dwarves) until the very end (i.e. a Big Rip). But if I understand you correctly, yes planets and moons will certainly stick around longer than main sequence stars. That is, stars that are currently undergoing the hydrogen-burning process (or nuclear fusion) like our sun. The lifetime of a star (how a star evolves through different phases) can vary greatly from a few million years to over a trillion years depending on its mass. As you might guess, the more massive stars will die out much more quickly because they rapidly consume their stores of hydrogen while smaller stars will stick around for a very long time.

Our sun is a G2 type star. The G2 comes from a standard classification system that astrophysicists use to classify stars and it developed from some older attempts along the way. Stars are primarily organized by effective temperature and mass (of course that also affects other properties such as luminosity and radius). The classes of stars are O, B, A, F, G, K, M ("Oh Be A Fine Girl, Kiss Me" is a popular mnemonic device to remember this) with O being the largest and M being the smallest. Scientists like to base units around familiar objects, so the units used here are Solar Mass, Solar Radius, Solar Luminosity (aka the mass, radius and luminosity of the sun). AU (astronomical unit) is also another popular unit which is the distance between the center of the earth and the center of the sun. Also, those letters are further subdivided into types with a number appended to them (0-9). A 0 type star would be the largest in that class while a 9 type star would be the smallest. The sun is a G2 and is generally considered to be a white star in color (the yellow we see is primarily due to our atmosphere). G type stars are expected to last for about 10 billion years before expanding into a red giant (the sun is roughly 4.6 billion years old), so we still have some time. :P
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droneriot
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PostPosted: Mon Nov 28, 2016 6:51 pm 
 

Alpha Centauri is gone. It's history. It stopped existing.
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Zelkiiro
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PostPosted: Tue Nov 29, 2016 12:35 am 
 

Didn't they just change the name?
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droneriot
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PostPosted: Sun Jan 08, 2017 2:05 pm 
 

Here's a pic of Earth and Moon taken by the Mars Reconnaissance Orbiter:

Spoiler: show
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BrutalizerUtilizerOfTheShadows
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PostPosted: Fri Jan 13, 2017 1:40 pm 
 

droneriot wrote:
Alpha Centauri is gone. It's history. It stopped existing.


If that's something that you observed, then it happened approximately 4.367 years ago.
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droneriot
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PostPosted: Sun Jan 15, 2017 1:03 pm 
 

Since microsatellites/cubesats are becoming a big thing, the Japanese are developing a tiny rocket just for launching them. The first attempt failed today, but the idea is really neat, because it could be done so cheaply basically any company in the world could launch their own stuff into space.
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droneriot
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PostPosted: Mon Feb 27, 2017 6:20 pm 
 

Humans are returning to the Moon in 2018. Well, flying around it anyway.
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Face_your_fear_79
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PostPosted: Thu Mar 02, 2017 2:49 am 
 

How big is the universe? If we think of the earth as being the size of a single atom, how big would the universe be?

Answer. The atomic radius of a hydrogen atom is r = 53 pm (picometers).
The Earth's radius is R = 6,370 km.

The radius of the visible universe is roughly 14 billion light years (light travel distance; there are other measures of the size of the universe). Scaling it by a factor of r/R is simple arithmetic, which yields a radius of 1.1 million kilometers. This is about 170 times the size of the Earth, or nearly three times the distance to the Moon!!!!!!!!!!!!

In other words, if the Earth was reduced to the size of a hydrogen atom, the visible universe would still be larger than the Earth-Moon system, by a factor of three!!!!!!!!!!

As far as we know, the whole universe (not just the visible part) is either open or flat, so its size is infinite.

By the way, another scale comparison, perhaps a little less abstract, is to reduce the Earth to the size of a small grape, about 1 cm.

The Moon would be the size of a small peppercorn, orbiting about a foot from the grape representing the Earth.

The Sun would be the size of a large beach ball, roughly 100 meters away, which is about the size of a large football field. This beach ball would be so incredibly hot, even at this distance its radiated heat would be burning your skin!!!!!!!!!!!

Jupiter would be the size of an orange, about half a kilometer away.

Neptune would be a ping pong ball, some two miles from the football field.

The nearest star? It would be about 30,000 kilometers away. So on this scale, the distance from the beach ball representing the Sun to the beach ball that represents Alpha Centauri would be equivalent to traveling three quarters of the way around the Earth!!!!!!!!!!!!!!

And then it gets worse. The distance from the beach ball representing the Sun to the center of the Milky Way would be comparable to the actual distance between the Earth and the Sun. So if you shrink the Earth to the size of a small grape, you have shrunk the Milky Way to the scale of the solar system!!!!!!!!!!!!

And the visible universe would still be several ten light years across on this scale!!!!!!!!!!!!!!!

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Electric Death
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PostPosted: Sat Mar 04, 2017 2:34 am 
 

If the visible universe feels large, try imagining the non-observable part. This video might "help" to give you a scale. It feels scary yet awesome at the same time. Depressing yet it brings relevations.

Youtube: show

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Face_your_fear_79
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PostPosted: Thu Mar 09, 2017 3:19 am 
 

Thank you much for the video. I did learn a lot and had a little fun at the same time.

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Haunted Shirt
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PostPosted: Thu Mar 09, 2017 8:08 am 
 

My personal belief is that the universe is endless. I believe the explanation for an endless universe is something that is beyond our current understanding. I do think this explanation from 2007, given by physicists at the University of North Carolina is very interesting. As I said though I believe the true explanation of endless universe, is currently beyond our understanding.

http://www.unc.edu/news/archives/jan07/newmodel012907.html

Quote:
Endless universe made possible by new model

CHAPEL HILL – A new cosmological model demonstrates the universe can endlessly expand and contract, providing a rival to Big Bang theories and solving a thorny modern physics problem, according to University of North Carolina at Chapel Hill physicists.

The cyclic model proposed by Dr. Paul Frampton, Louis J. Rubin Jr. distinguished professor of physics in UNC’s College of Arts & Sciences, and co-author Lauris Baum, a UNC graduate student in physics, has four key parts: expansion, turnaround, contraction and bounce.

During expansion, dark energy -- the unknown force causing the universe to expand at an accelerating rate -- pushes and pushes until all matter fragments into patches so far apart that nothing can bridge the gaps. Everything from black holes to atoms disintegrates. This point, just a fraction of a second before the end of time, is the turnaround.

At the turnaround, each fragmented patch collapses and contracts individually instead of pulling back together in a reversal of the Big Bang. The patches become an infinite number of independent universes that contract and then bounce outward again, reinflating in a manner similar to the Big Bang. One patch becomes our universe.

“This cycle happens an infinite number of times, thus eliminating any start or end of time,” Frampton said. “There is no Big Bang.”

An article describing the model is available on the arXiv.org e-print archive and will appear in an upcoming issue of Physical Review Letters. The work was supported in part by a U.S. Department of Energy grant.

Cosmologists first offered an oscillating universe model, with no beginning or end, as a Big Bang alternative in the 1930s. The idea was abandoned because the oscillations could not be reconciled with the rules of physics, including the second law of thermodynamics, Frampton said.

The second law says entropy (a measure of disorder) can’t be destroyed. But if entropy increases from one oscillation to the next, the universe becomes larger with each cycle. “The universe would grow like a runaway snowball,” Frampton said. Each oscillation will also become successively longer. “Extrapolating backwards in time, this implies that the oscillations before our present one were shorter and shorter. This leads inevitably to a Big Bang,” he said.

Frampton and Baum circumvent the Big Bang by postulating that, at the turnaround, any remaining entropy is in patches too remote for interaction. Having each “causal patch” become a separate universe allows each universe to contract essentially empty of matter and entropy. “The presence of any matter creates insuperable difficulties with contraction,” Frampton said. “The idea of coming back empty is the most important ingredient of this new cyclic model.”

This concept jolted Frampton when it popped into his head last October.

“I suddenly saw there was a new way of solving this seemingly impossible problem,” he said. “I was sitting with my feet on my desk, half-asleep and puzzled, and I almost fell out of my chair when I realized there was a much, much simpler possibility.”

Also key to Frampton and Baum’s model is an assumption about dark energy’s equation of state -- the mathematical description of its pressure and density. Frampton and Baum assume dark energy’s equation of state is always less than -1. This distinguishes their work from a similar cyclic model proposed in 2002 by physicists Paul Steinhardt and Neil Turok, who assumed the equation of state is never less than -1.

A negative equation of state gives Frampton and Baum a way to stop the universe from blowing itself apart irreversibly, an end physicists call the “Big Rip.” The pair found that in their model, the density of dark energy becomes equal to the density of the universe and expansion stops just before the Big Rip.

New satellites currently under construction, such as the European Space Agency’s Planck satellite, could gather enough information to determine dark energy’s equation of state, Frampton said.
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droneriot
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PostPosted: Thu Mar 09, 2017 8:18 am 
 

Here's a good explanation, though I believe it was written before dark matter and dark energy became a big topic:

http://www.hawking.org.uk/the-beginning-of-time.html

Quote:
In fact, James Hartle of the University of California Santa Barbara, and I have proposed that space and imaginary time together, are indeed finite in extent, but without boundary. They would be like the surface of the Earth, but with two more dimensions. The surface of the Earth is finite in extent, but it doesn't have any boundaries or edges. I have been round the world, and I didn't fall off.

(That's just a sample, best to read the whole thing, it only takes ten minutes.)
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GTog
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PostPosted: Sun May 07, 2017 10:34 pm 
 

It's possible that my eyes have undergone permanent damage from all the rolling they've done whenever "dark matter" comes up. Its existence is only posited because some cosmological observations don't seem to quite line up with existing theory. Somehow or another, a generation of physicists have decided that instead of the theory not being right, it must be that the entire universe is radically different the previously supposed.

The greatest unanswered question in science is, to me, not "dark" anything, but rather how thousands of otherwise very smart people could possibly think that is a reasonable conclusion.

Dutch physicist Erik Verlinde is on the right track, I think. He proposed recently (like, 6 months ago recently) that gravity may actually be an emergent phenomenon that arises due to differences in entropy between configuration spaces. Not a fundamental force really, or spacetime bending caused by mass.

The theory has a long way to go before it gains any serious traction. But there has already been at least one large scale re-analysis of galactic data, which concluded that gravitational lensing at least can be explained just fine by this new theory, no need for "dark matter".
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droneriot
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PostPosted: Mon May 08, 2017 3:47 am 
 

It's only radical if you believe that God created the universe for humanity or something. It's matter that cannot (currently) be measured by humans, yeah how radical.
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GTog
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PostPosted: Mon May 08, 2017 11:07 am 
 

droneriot wrote:
It's only radical if you believe that God created the universe for humanity or something. It's matter that cannot (currently) be measured by humans, yeah how radical.


"Dark matter" is, and always has been, a fudge. What happened is that astronomers made some observations that just didn't fit with current theory. Nobody had any idea how to formulate a whole new theory from scratch that could explain them. So instead of a new theory, they asked themselves what it would take to adjust the data so current theory still worked.

These adjustments are what is called "dark matter". Its proposed properties have no scientific justification whatsoever. They were made up out of nowhere simply to get the math to work out.

The physicists aren't exactly cheating though, because they didn't stop there. The intention always has been to use those hypothetical properties to reverse engineer a new theory that can explain them. Maybe they will someday, maybe they won't. But don't lose sight of the fact that "dark matter" is nothing more than some hypotheticals jammed into some equations to see what would happen.
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Dudemanguy
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PostPosted: Mon May 08, 2017 1:21 pm 
 

Dark matter is not "made up out of nowhere." When you can explain the fact that rotational curves in the galaxy do not obey the inverse square law, gravitational lens observations, and a ton of other observational evidence without the use of dark matter, be sure to submit your paper and get your Nobel Prize. You can complain that it's ad hoc and a hypothetical (note that plenty of things well-accepted in modern physics were originally ad hoc, e.g. neutrinos), but it's mostly irrelevant as nobody is going to throw out centuries of well-supported physics because of some observations that don't totally match up. The natural response is to assume there is a missing parameter.
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GTog
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PostPosted: Mon May 08, 2017 4:41 pm 
 

Dudemanguy wrote:
Dark matter is not "made up out of nowhere." When you can explain the fact that rotational curves in the galaxy do not obey the inverse square law, gravitational lens observations, and a ton of other observational evidence without the use of dark matter, be sure to submit your paper and get your Nobel Prize. You can complain that it's ad hoc and a hypothetical (note that plenty of things well-accepted in modern physics were originally ad hoc, e.g. neutrinos), but it's mostly irrelevant as nobody is going to throw out centuries of well-supported physics because of some observations that don't totally match up. The natural response is to assume there is a missing parameter.


Well, no, but that's not really the point.
The point is that "dark matter" is not predicted by theory. What I said about its origins is 100% true - it is simply a set of adjustments made to data to see what it would take to make some wonky observations fit existing theory.

Neutrinos were never hypothetical. They were theoretical, which is a whole different thing. They were very nicely predicted by theory.
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Dudemanguy
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PostPosted: Mon May 08, 2017 5:02 pm 
 

Nonsense. Neutrinos are just as guilty of being ad hoc as Dark Matter. Instead of saying "we got to modify energy conservation," Pauli said "well let's just suppose this particle exists so that beta decay doesn't violate all of our conservation laws." Of course, Pauli turned out to be right, but it's still ad hoc.

Dark Matter is similar. When it was discovered that galaxies didn't fit the viral theorem, it was hypothesized that there must be some extra unseen mass. And there is, of course, tons of evidence for its existence regardless of whether you like it or not. If you want to dabble in quack physics that modify general relativity or something, feel free. But understand that you're being just as ad hoc and modifying existing theory to fit data (which is what you're supposed to do in physics).
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Face_your_fear_79
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PostPosted: Sat Jun 10, 2017 10:41 pm 
 

My opinion on whether the Universe is infinite or not is no. Yes its a complete guess on my part but a infinite Universe does not make sense to me. I guess there has to be a edge to it and a end.

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Nhor
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PostPosted: Mon Jul 24, 2017 11:19 am 
 

the jury's still out on that, everything from popsci books to the classroom can only speculate right now

I suspect it's not infinite though, because infinities are never found in nature (something repeated in all of my physics courses thus far)

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Zelkiiro
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PostPosted: Mon Jul 24, 2017 11:26 pm 
 

My Super-Valuable Hot Take:

The universe is, in fact, infinite. Beyond the contents we know of, there's just empty space reaching out forever and ever--or, y'know, other stuff we can't see yet.
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Napero
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PostPosted: Tue Jul 25, 2017 6:37 am 
 

Face_your_fear_79 wrote:
My opinion on whether the Universe is infinite or not is no. Yes its a complete guess on my part but a infinite Universe does not make sense to me. I guess there has to be a edge to it and a end.

Hint of the day: in scientific things, choosing to believe something just because it feels comfortable is not the way to go.

Universe can be of finite size, but there is no "edge" to it. Just like there's no center. If you look for the place where the big bang took place, it's simply everywhere.

Zelkiiro wrote:
My Super-Valuable Hot Take:

The universe is, in fact, infinite. Beyond the contents we know of, there's just empty space reaching out forever and ever--or, y'know, other stuff we can't see yet.

No. The expanding universe does not expand into something. There is nothing outside the universe to expand into. It just stretches within itself. All the locations withing the universe are essentially similar, and as far from the supposed edges as everything else.

Funny, ain't it?
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Face_your_fear_79
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PostPosted: Wed Jul 26, 2017 1:41 am 
 

Napero wrote:
Face_your_fear_79 wrote:
My opinion on whether the Universe is infinite or not is no. Yes its a complete guess on my part but a infinite Universe does not make sense to me. I guess there has to be a edge to it and a end.

Hint of the day: in scientific things, choosing to believe something just because it feels comfortable is not the way to go.

Universe can be of finite size, but there is no "edge" to it. Just like there's no center. If you look for the place where the big bang took place, it's simply everywhere.

Zelkiiro wrote:
My Super-Valuable Hot Take:

The universe is, in fact, infinite. Beyond the contents we know of, there's just empty space reaching out forever and ever--or, y'know, other stuff we can't see yet.

No. The expanding universe does not expand into something. There is nothing outside the universe to expand into. It just stretches within itself. All the locations withing the universe are essentially similar, and as far from the supposed edges as everything else.

Funny, ain't it?


Thanks Napero. I am trying learning as I go. Unfortunate I will never come close to having any answers because it is just way to complicated for my lack of education.

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