Space is really really big.

[Ray McCarthy]

Curiously this article claims Milky Way is 100,000 LYs diameter, while many estimates are 150,000LY to 180,000 LY. Part of the problem is that there is no definite edge and newer observations find more stars in the darker bits between arms and more beyond the previous "edge". As the article explains, many distances are averages of different methods that don't agree.

There also seems to be a lack in emphasis of how interstellar and inter-galactic dust and gas can skew brightness and red-shift measurements.

You'd think that Cepheid variability would get round that issue.

In the early 1920s, Edwin Hubble detected Cepheid variables in the nearby Andromeda galaxy and discerned that it was just under a million light years away.

That's probably half the distance. We don't know for sure how accurate the idea of using Cepheids is.

However the observable Universe (in radio rather than visible light) is very large.
It took centuries, but we now know the size of the Universe

Now comes the big key to our puzzle. The most redshifted light we can detect in the observable Universe suggests that light has reached us from galaxies that are 13.8 billion light years old.
Because this is the oldest light we have detected, that also gives us a measurement for the age of the Universe itself.

No mention that the Red Shift is accentuated at greater distances due to dust and gas. Though they do say:

One possibility is that, somewhere, a few of our calculations are not quite right

Conclusion

But over the last 13.8 billion light years, the Universe has been continually expanding – ... astronomers have worked out that the galaxies right on the edge of the observable Universe, whose light has taken 13.8 billion years to reach us, must now be 46.5 billion light years away.
That is our best measurement for the radius of the observable Universe. Doubling it, of course, gives the diameter: 93 billion light years.

Finally, making various assumptions, that may or may not be true:

The result, after using computer algorithms to look for meaningful patterns in the data, was a new estimate. The whole Universe is roughly 250 times as large as the observable Universe.
...
But estimates and models aside, we just do not know

 

[Ray McCarthy]

I think then that works out as an estimate of 11,625 Billion Light years diameter? Unless the 250 times is volume.
The observable universe has an estimated 10 thousand million galaxies or a thousand, million, million, million stars.
If the "big bang" means a roughly spherical distribution, though individual galaxies can be globular or spiral discs, then 250 times larger diameter is 1,170,000 larger volume. I'm not sure if "250 times as large" is volume or diameter. Still even it it was volume, and you could check 6 stars every second for life that would take over 10,000 billion years.

Harder to believe we are unique in being the only planet with industrialised civilisation.

 

[Dennis E. Taylor]

Arguments about life on other worlds come down to three questions:

- Does life exist elsewhere
- Does intelligence exist elsewhere
- Does intelligence exist elsewhere that's close enough to us to make a difference

The last one is important, because an industrialized civilization 13 billion light years away is not visiting us, even if they do have some kind of FTL.

All too often, the arguments for UFOs being ET hinge on the "high probability of life elsewhere in the universe." A more accurate way to look at it would be "probability of intelligent, industrialized life within a few hundred light years of us." I still can't say what the probabilities are for each alternative, but I can say the probability is much lower for the latter.

 

[Ray McCarthy]

Does intelligence exist elsewhere that's close enough to us to make a difference

Unlikely. Anyway that's irrelevant to the question of Intelligent life. That's part of the question, of "Intelligent life exists, (say verified by spectroscopic surveys in next 10 years), can we communicate or visit?" The answer is "probably not", unless we discover some science we have no inkling of today.


Even if Civilisations are "common", space is too big to not only allow travel (unless the unlikely "starships" exist) but even too big for practical radio or laser communications.

"probability of intelligent, industrialized life within a few hundred light years of us."

Low. and even more than maybe 20 Light years isn't practical for travel or communication.

 

[Brian G Turner]

The last one is important, because an industrialized civilization 13 billion light years away is not visiting us, even if they do have some kind of FTL.

The Fermi Paradox. Ralph Kern looked to address this directly in his novel Endeavour, which I thought was very well done.

 

[tinkerdan]

Going back to the article: I was just thinking that there should be a warning--things in the mirror are closer than they appear--or further--or both--or neither. Maybe!

 

[Vaz]

Your post reminded me if the infamous Jurassic Park T-Rex chase scene. Dino's in space?

 

[Extollager]

This discussion is heading towards some matters to which my thoughts often return.

I suspect that many people think it is just a matter of time (and willingness to spend some money) before we find certain evidence of intelligent life on other planets. This idea is, I have no doubt, part of the basic mental outfit of many people.

Now how might people's emotional and imaginative lives be affected if, let's say 50 or a hundred or 200 years from now, there remains absolutely no real evidence for intelligent life on any other planet?



I do wonder if we are not going to have some interesting adjustments to make as we reach various barriers/records/limits, since the assumption of so many seems to be that our species will just go on and on achieving breakthroughs of various kinds.

But in fact there are all sorts of limits in nature. It may be that on average people are taller now than a thousand years ago. But we will not just keep getting taller. We may beat the record for running the mile on earth with its gravity. But the record is not infinitely capable of being superseded, i.e. we'll never get to the point that an athlete will run the mile in 5 seconds. We are used to records being broken, but what if gradually more and more records (in athletics, in lifespan, etc.) just are not passed? How will that affect people?


I also wonder: suppose we did detect, say, radio waves that had to be interpreted as evidence of intelligent life on some other world. Might we end up having to live with that knowledge for decades or centuries and not know where they had come from or what they meant? Because aside from mathematical data perhaps, I don't see how you really are going to translate a completely new language without some kind of Rosetta Stone or actual contact. Would it not haunt people (and no doubt spur a lot of crackpot activity) to have recordings of broadcasts from some planet lost in the depths of space, and be utterly unable to figure out their meaning?

We would also know that the broadcasts are ancient, but probably not be able to figure out how ancient. Right?

Brrrr!

 

[J Riff]

How about: How long has intelligent life been here, in touch with da Earth in various ways. I think the arrogance of humans has gone on long enough.
I will guesstimate, ohhhh say, maybe... 69,852 intelligent races, so far, in this galaxy alone. And most of it really alien, kind of like most of the biomass on Earth - no light, no using sound or vision. Life unique to the Earth? Howls of derisive laughter, Bruce.
So, how big is the next 'dimension' up then, if it contains this one?
It sure is nice to see some uncertainty there, in the numbers and distances, because BIG, yes!

 

[The Ace]

"You may think it's a long way down to the Post Office, but that's just peanuts compared to Space." Douglas Adams, "The Hitch-Hiker's Guide to the Galaxy."

 

[Ray McCarthy]

I also wonder: suppose we did detect, say, radio waves that had to be interpreted as evidence of intelligent life on some other world.

We discussed that elsewhere, Radio is almost certainly not going to happen, basic physics is against it. Spectroscopic analysis showing likely life without industrialisation, or life & Industrialisation might be just possible with existing telescopes and certainly with the next big space telescope, the James Webb.

Currently there is no Fermi Paradox, because the distances are too far for radio and we have only started Spectroscopic surveys that are barely good enough.

The distances and number of stars are also such that even if a civilisation figured a starship "interstellar" system that some how wiggles around the light speed barrier, their starship would have to be dispatched because they noticed our spectroscopic signal. That however is only so far visible just over 100LY away. So even should such starships be possible, statistically it could be thousands of years before out industrially affected spectrum reaches anyone.

If we do discover possible evidence, then the likelihood is that without fictional "stardrive" becoming a reality, we can't communicate, except perhaps with a robot probe that might take thousands of years to transit.

Perhaps interstellar travel is for all practical purposes impossible, so in reality we are all in "quarantine" Who knows.

 

[J Riff]

Will the human race advance far enough to reveal ET before we all expire, that's all I care about, at this precise moment. )
Think of the odds against hitting the 100 yr. envelope where that happened. Anyone opposed to such an event is gots to be the enemy - and he is us.
But, the bigness.... hey, can anyone here actually measure, say, the distance to Mars - by yourself? Or do we always take the handouts from the official types? How would you measure that, bounce a beam off it? How, huh?

 

[Ray McCarthy]

I maybe could bounce a beam off the moon, though I've not tried. Mars is too far for any normal home system, you can use orbital mechanics, Kepler's law to decide how far away anything is in the solar system from orbital period and assuming mass is a small fraction of the sun.
Nearer stars can perhaps be estimated by parallax using two telescopes "far" apart, that's not easy as for a long time astronomers couldn't measure any parallax for stars

Stars, unlike planets, seem invariable in position as we orbit the sun. That puts them very far away.

EME on a Budget: Moonbounce for the Rest of Us
EME / Moonbounce for a beginner? | QRZ Forums

Think of the odds against hitting the 100 yr. envelope where that happened. Anyone opposed to such an event is gots to be the enemy - and he is us.

That doesn't make sense. You are the Man from Mars and I claim my $10
There is no 100 yr envelope.

 

[Vertigo]

I believe any amateur astronomer with a working knowledge of orbital mechanics can figure Mar's orbit just from observations. And from that Mar's distance to Earth at any particular time can very easily be calculated. There's no conspiracy there I'm afraid. All the planetary orbits were calculated long ago and using equipment little better than many modern amateur astronomers possess to make the observations.

 

[J Riff]

The 100 yeArs is our lifetime, lucky us. No conspiracy, just, can you do it, with no external assistance.

 

[Ray McCarthy]

Another article showing that "scientists"* have got too specialist and don't involve experts enough?

Astronomers at Cornell University in the US have developed a new equation which seeks to explain the Fermi Paradox, a philosophical conundrum which asks why extra-terrestrials have not been in touch if billions of Earth-like planets exist in our galaxy.
Essentially, if the universe is teeming with aliens, as predicted, where is everyone?
The scientists have calculated that signals from Earth would need to reach half of all the Sun systems in the Milky Way to be sure of being picked up by an advanced civilisation. And that is unlikely to happen for 1,500 years.

But already the oldest signal's potential distance is such that the signals are lost in the noise. They are ignoring basic thermodynamics!

See
Aliens unlikely to be in contact for 1,500 years, scientists calculate

“We haven’t heard from aliens yet, as space is a big place but that doesn’t mean no one is out there,” said student Evan Solomonides , who is presenting the equation at Astronomical Society’s meeting June 16 in San Diego.

So a student and not a Scientist Astronomer! My emphasis.

So far Earth’s broadcast signals have reached every star within about 80 light-years from the Sun, around 8,531 stars and [perhaps] 3,555 Earth-like planets. But our Milky Way galaxy alone contains 200 billion stars so there is still a long way to go.
However Mr Solomonides is optimistic because of the Mediocrity Principle, which suggests that Earth is unlikely to be unique in the Universe.

The basic idea that statistically another "technological civilisation" is unlikely in the current 80 light year radius is reasonable. The idea that anything could be detected even as far away as 20 LY isn't very reasonable at all as I previously explained**.

[A missing "perhaps" from the number of planets which is speculation]

@J Riff will like the headline photo


[* Careful reading suggests the newspaper is misleading and it's not a suggestion by qualified scientists at all]
[** I'm not a scientist or astronomer, I'm a Communications Engineer by training, so I know more about radio signals and what is possible even with hypothetical perfect equipment and radio than an astronomer]

 

[Brian G Turner]

I've often wondered if any property of the Oort Cloud and solar boundary might naturally impede or weaken any broadcasting signals.

 

[Ray McCarthy]

I've often wondered if any property of the Oort Cloud and solar boundary might naturally impede or weaken any broadcasting signals.

Short answer: No. Not at all for either.

Longer answer:
It's an incredibly sparse globular "shell". Clue ... It's hard to detect. Starlight and radio from stars isn't impeded. On average it's a 1000x further away than the Kuiper belt. So though the total mass might be high, it's very spread out.
Even the more band like Kuiper belt has no significant effect.

A chain link fence or chicken wire mesh will stop UHF TV (0.47 to 0.8GHz). The street light poles won't as spacing is too high. You can make a UHF dish from chicken mesh, but not a Sky satellite dish (10.7 to 12.6GHz, Ku Band). At the right angle you can see through a Sky perforated dish, which is pretty useless for Ka band satellite (20GHz). The spacing of the objects in the Oort cloud is maybe millions of km. It's almost invisible. Artists impressions of it are very misleading.

The "solar boundary" is really an "ending" due to inverse square law, where the solar wind and solar radiation is becoming insignificant compared to cosmic radiation. It's not a physical boundary as such, more gradual absence of the environment of the solar system. The inner Oort cloud seems to be a good distance beyond this point.

Thus there have been many news items on Voyager "leaving" the Solar system.

Question: Where do we consider our solar system to end; Pluto's orbit? Solar apex?



Answer: The solar system may be broadly defined as consisting of all those objects that are ultimately governed by the gravitational field of the Sun. In addition to the planets, moons, asteroids and dust of the planetary system, it includes the distant bodies of the Kuiper Belt and Oort cloud, the later extending perhaps as far as 50,000 astronomical units (1 AU = about 93 million miles). The gravitational influence of the Sun may extend as far as 2 light years. (From "Solar System", James H. Shirley, in Encyclopedia of Planetary Science).

That said, Pluto (and sometimes Neptune) is the most distant planet in our Planetary System. The Voyagers passed the orbit of Neptune (which was furthest at the time) in August 1989. Neither flew by Pluto, which was elsewhere in its orbit at the time.

Another concept is the heliosphere, which is a bubble around the Sun created by the outward flow of the solar wind from the sun and the opposing inward flow of the interstellar wind. That heliosphere is the region influenced by the dynamic properties of the sun that are carried in the solar wind - such as magnetic fields, energetic particles, solar wind plasma, etc. We don't know how big the heliosphere is and that is something the Voyagers could help us define. At the point where the two winds meet, a shock is created and this termination shock would mark the beginning of the heliopause, where the two winds interact. Voyager 1 could encounter the termination shock in the next 2-3 years. Beyond the heliopause is interstellar space. It is possible that one of the Voyagers could enter into interstellar space before 2020 when we will no longer have enough electrical energy to power the instruments.



Question: Where are the spacecrafts Voyager I and II today? Are they far from the Solar System, i.e., free from the Sun's gravitational field?



Answer: See the link on the Voyager website called "Latest Weekly Status Report and Distance & Velocity Information". It includes distances from the Sun, round-trip light times and velocities for both spacecraft. The info tends to be three-to-four weeks old, but it doesn't really change that quickly. Voyager 1 is the furthest away but is still within the region dominated by the Sun and its solar wind and is still considered to be within the solar system. Both spacecraft have, however, passed the farthest known planets within our solar system - when Voyager 2 passed Neptune in 1989. To see today's distances and locations for the Voyagers and the Pioneers, go to Spacecraft escaping the Solar System

Voyager FAQ - The Interstellar Mission

Spacecraft escaping the Solar System

    Pioneer 10    Pioneer 11    Voyager 2    Voyager 1    New Horizons
Distance from Sun (AU)    116.177    95.282    111.411    135.261    35.694
Speed relative to Sun (km/s)    11.980    11.292    15.374    17.000    14.379
Speed relative to Sun (AU/year)    2.527    2.382    3.243    3.586    3.033
Ecliptic latitude    3°    14°    -36°    35°    2°
Declination    25° 55'    -8° 38'    -57° 26'    12° 27'    -20° 36'
Right ascension    5h 10m    18h 49m    20h 0m    17h 12m    19h 6m
Constellation    Taurus    Scutum    Pavo    Ophiuchus    Sagittarius
Distance from Earth (AU)    117.186    94.344    110.662    134.440    34.742
One-way light time (hours)    16.24    13.08    15.34    18.64    4.82
Brightness of Sun from spacecraft (Magnitude)    -16.4    -16.8    -16.5    -16.0    -18.9
Spacecraft still functioning?    no    no    yes    yes    yes
Launch date    1972-Mar-03    1973-Apr-06    1977-Aug-20    1977-Sep-05    2006-Jan-19

The region can be subdivided into a spherical outer Oort cloud of 20,000–50,000 AU (0.32–0.79 ly), and a torus-shaped inner Oort cloud of 2,000–20,000 AU (0.0–0.3 ly). The outer cloud is only weakly bound to the Sun and supplies the long-period (and possibly Halley-type) comets to inside the orbit of Neptune.

Oort cloud - Wikipedia, the free encyclopedia

So Voyager 1 is 135 AU away and the Oort Cloud is 2,000 to 50,000 AU away!
The Kuiper belt is 30 AU to 50 AU away

 

[Brian G Turner]

It's not a physical boundary as such, more gradual absence of the environment of the solar system.

The reason I ask is that I remember vaguely from science lessons at school that one way in which radio is used for communication is by utilising differences in atmospheric density to "bounce" radio signals around the globe.

I wondered if it may be possible that the solar boundary may result in a similar phenomenon of scattering, even diffusing signals. I know it's not a strong analogy, and the density of mass in open space is tiny - but if a change in density by any magnitude can result in radio being reflected, then any similar process at the solar boundary would present a natural explanation for the Fermi Paradox.

Then again, perhaps the natural weakening of our own broadcasts is process enough - that no one would necessarily know we are here - and conversely, we'd struggled to detect similar from other civilisations.

 

[Ray McCarthy]

The reason I ask is that I remember vaguely from science lessons at school that one way in which radio is used for communication is by utilising differences in atmospheric density to "bounce" radio signals around the globe.

I wondered if it may be possible that the solar boundary may result in a similar phenomenon of scattering, even diffusing signals.

The Inverse square law, natural geometry and thermodynamics. Even at the nearest stars, under 5 LY, receiving our ordinary signals would be almost impossible. It's not a matter of technology. The frequencies of ordinary broadcasts are too low for efficient use of dishes. You'd need a specially designed microwave system with enormous power and dishes for even the nearest star!

The variations you are speaking of are the ionosphere. It has a MUF (Maximum Usuable Frequency) which is usually below 30MHz. It's created by the effect of the solar wind on our magnetosphere. Such a thing actually has no effect at higher frequencies useful for space (above 200MHz and ideally above 2GHz, 2000MHz).
The so called "Solar Boundary" isn't a layer or layers like the layers in the ionosphere, it's simply a very large region were the solar wind ceases to be significant. Solar wind not of much significance at all to radio unless there is a strong magnetic field, which there isn't out there. Even then, only lower frequencies no use for space communication are affected. There is also solar radiation (Light, UV, X-Rays, IR, Radio), they have no "boundary". The Sun is point radiation omni-directional source and as such its considerable interference follows the inverse square law. It's very powerful, so someone 1000s of LY away can detect our planets transiting the sun and 150 LY away see the pollution in our atmosphere in 1866 using spectroscopic analysis.

Summary:

1. It's fantasy to think that ordinary broadcast signals (too weak and wrong band) can be picked up at other stars, or we could receive their ordinary signals.
2. Even a specially made specialist "ideal" system intended for interstellar radio would be "short range" and only work while the dishes at each end are pointed exactly at each other at the right time. You'd be very limited with a planet bound system due to rotation.
3. The Solar Boundary, Kuiper Belt and Oort cloud are all irrelevant.
4. Our Ionosphere means that frequencies above 30MHz are better. Cosmic noise means frequencies above 1000MHz are better. Certain frequencies are absorbed badly by air and especially moisture. Radio Telescopes avoid those.
5. Earth based interference is an issue. There are areas where no radio devices are allowed. That's for signals from stars which are hugely stronger than anything artificial