Starship Asterisk*

Chris Peterson wrote:

rstevenson wrote:
The phrase I prefer for describing the universe is "finite but unbounded". It seems to cover the ground.

It could be finite or infinite, it could be bounded or unbounded. These questions remain unanswered.

• It can't be infinite and bounded;
  
  though it can be infinite & bounding
  (at the Quantum foam level)
  
  Sailing, sailing,
  Over the bounding main,
  For many a stormy wind shall blow
  Ere Jack comes home again,

rstevenson wrote:The phrase I prefer for describing the universe is "finite but unbounded". It seems to cover the ground.

Ann wrote:

Chris Peterson wrote:

heehaw wrote:It looks very much as if the Universe is infinite in size, from the microwave background results. If that is so, there are infinitely many Earth-like planets, including infinitely many on which there is a US election underway at the moment. If the Universe is BIG but is not infinite, then we don't know how many Earth-like planets there are bearing life.

How does the nature of the microwave background argue for an infinite sized universe? As we lack any observations outside the observable universe, and our cosmological theory is very incomplete in some respects, I'd suggest that we really have no idea at all beyond speculation whether the Universe itself is finite or infinite.

The way I understand it, Chris, the microwave background argues for a flat, ever-expanding, Lambda Cold Dark Matter universe. Such a universe is at least "expanding into" infinity.

Chris Peterson wrote:

heehaw wrote:It looks very much as if the Universe is infinite in size, from the microwave background results. If that is so, there are infinitely many Earth-like planets, including infinitely many on which there is a US election underway at the moment. If the Universe is BIG but is not infinite, then we don't know how many Earth-like planets there are bearing life.

How does the nature of the microwave background argue for an infinite sized universe? As we lack any observations outside the observable universe, and our cosmological theory is very incomplete in some respects, I'd suggest that we really have no idea at all beyond speculation whether the Universe itself is finite or infinite.

Chris Peterson wrote:... and the fact that planetary systems are chaotic and planets can apparently move suddenly and rapidly into very different orbits ...

heehaw wrote:It looks very much as if the Universe is infinite in size, from the microwave background results. If that is so, there are infinitely many Earth-like planets, including infinitely many on which there is a US election underway at the moment. If the Universe is BIG but is not infinite, then we don't know how many Earth-like planets there are bearing life.

neufer wrote:

Ann wrote:

neufer wrote:

When I say earthlike planets, I mean truly earthlike planets. I mean planets with a robust biosphere. How many such planets are there in the Milky Way?

---

• Oh...in that case: 5.

MarkBour wrote:It seems most sensible to assume that our Solar system coalesced from a fairly homogeneous cloud of material. Is there a simulation that has been done that could start from such a cloud and come anywhere close to explaining the differing compositions of our star and planets et al, as one moves from the center outward?

The next question would be, how could the Cancri 55 system, a mere 40 light years away, come up with a planet that is so different in composition? Or does that fit our own system, were a large planet to have formed inside the orbit of Mercury?

rstevenson wrote:

Ele6 wrote:

APOD Robot wrote:this exoplanet is not made primarily of oxygen, as are the inner planets in our Solar System

Oxygen?

From the Wikipedia article on Earth ...

[Earth] is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%), with the remaining 1.2% consisting of trace amounts of other elements.

Of course, most of that oxygen is bound up in compounds such as silica, alumina, lime, and so on.

Rob

MrZorg wrote:HA. this is a funny post. As IF... we can tell a planet it tidal locked 40 light years away, but can't find planet X which we have been searching for since the late 1800's... don't you find that funny?

rstevenson wrote:From the Wikipedia article on Earth ...

[Earth] is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%), with the remaining 1.2% consisting of trace amounts of other elements.

Of course, most of that oxygen is bound up in compounds such as silica, alumina, lime, and so on.

Ele6 wrote:

APOD Robot wrote:this exoplanet is not made primarily of oxygen, as are the inner planets in our Solar System

Oxygen?

[Earth] is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%), with the remaining 1.2% consisting of trace amounts of other elements.

The planet orbits its 40 light-year distant Sun-like star well inside the orbit of Mercury, so close that it is tidally locked, meaning that it always keeps the same face toward the object it orbits -- like our Moon does as it orbits the Earth.

Ann wrote:

neufer wrote:

Ann wrote:
How rare is Earth really?

https://en.wikipedia.org/wiki/Kepler_%28spacecraft%29 wrote:
<<In March 2011, astronomers at NASA's Jet Propulsion Laboratory (JPL) reported that about "1.4 to 2.7 percent" of all Sun-like stars are expected to have earthlike planets "within the habitable zones of their stars". This means there are "two billion" of these "Earth analogs" in the Milky Way alone.

When I say earthlike planets, I mean truly earthlike planets. I mean planets with a robust biosphere. How many such planets are there in the Milky Way?

• Oh...in that case: 5.