The time it takes for light to travel back to earth

euser1984

Someone was telling me that light takes about an hour or so to travel to earth from Saturn.

Does this mean if I am looking at it through a telescope, that I'm seeing something that happened an hour or so ago?

Thanks.

cruizer101

Yeah, its kinda crazy when you think about, looking into the past.

Some of the stars we see might not exist anymore because they are so far away the light that is currently reaching us may be from ages ago when they still did exist.

Even the light from the sun is about 8 minutes old when it reaches us

euser1984

So that means that if we were far enough away from earth with a massive telescope where the light has travelled to we could see dinosaurs?

murphyme2010

In principle, yes.
You would need a VERY big telescope though to see T-Rex:)

There are objects which have been gravitationally lensed in such a way that we see two images of the object but the light path for the two images is different and thus we see the same object at two different times.

Hijpo

If it takes the suns rays 84 minutes to reach Saturn, then another 10 minutes for the light from saturn to reach earth, does that mean we see saturn an hour and a half after the light hits it?

Nerro

euser1984 wrote: »

So that means that if we were far enough away from earth with a massive telescope where the light has travelled to we could see dinosaurs?

Not quite, unless you can actually travel faster than speed of light
The light from time of the dinosaurs already left earth and its millions of light years away already ,since nothing can travel faster than light you will never catch it.

euser1984

Is einsteins space time related to this in anyway? Or theories about black holes?

euser1984

Nerro wrote: »

Not quite, unless you can actually travel faster than speed of light
The light from time of the dinosaurs already left earth and its millions of light years away already ,since nothing can travel faster than light you will never catch it.

Maybe there is somebody over there already though, like part of our mind :eek:

RebelButtMunch

Hijpo wrote: »

If it takes the suns rays 84 minutes to reach Saturn, then another 10 minutes for the light from saturn to reach earth, does that mean we see saturn an hour and a half after the light hits it?

Nope. You see saturn ten mins ago. Unlesd someone on saturn had a mirror pointed at the sun. Then you would see the sun in the mirror as it was 94 mins ago

Capt'n Midnight

Back in 1676
http://galileoandeinstein.physics.virginia.edu/lectures/spedlite.html

The first real measurement of the speed of light came about half a century later, in 1676, by a Danish astronomer, Ole Römer, working at the Paris Observatory. He had made a systematic study of Io, one of the moons of Jupiter, which was eclipsed by Jupiter at regular intervals, as Io went around Jupiter in a circular orbit at a steady rate. Actually, Römer found, for several months the eclipses lagged more and more behind the expected time, but then they began to pick up again. In September 1676,he correctly predicted that an eclipse on November 9 would be 10 minutes behind schedule. This was indeed the case, to the surprise of his skeptical colleagues at the Royal Observatory in Paris. Two weeks later, he told them what was happening: as the Earth and Jupiter moved in their orbits, the distance between them varied. The light from Io (actually reflected sunlight, of course) took time to reach the earth, and took the longest time when the earth was furthest away. When the Earth was furthest from Jupiter, there was an extra distance for light to travel equal to the diameter of the Earth’s orbit compared with the point of closest approach. The observed eclipses were furthest behind the predicted times when the earth was furthest from Jupiter.

ps200306

euser1984 wrote: »

Someone was telling me that light takes about an hour or so to travel to earth from Saturn.

Does this mean if I am looking at it through a telescope, that I'm seeing something that happened an hour or so ago?

Thanks.

This leads to the conclusion that everything you see is in your past. Your outstretched hand is about two nanoseconds in your past. From O'Connell bridge, the light on the top of the Spire is a microsecond ago. The sound of Big Ben on the BBC News by radio from London is one and a half milliseconds ago. The signal from the Sky TV satellite is a tenth of a second ago, and the moon is a second and a half ago.

Things get complicated when you start moving. If you go from O'Connell Bridge to the dining hall in Trinity College, the Spire is now two microseconds ago instead of one. Suppose someone claps their hands on the top of the Spire and you witness this from O'Connell Bridge. That clap is still a microsecond in the future of someone at the dining hall. Let's suppose you yourself travel at the speed of light from O'Connell bridge to the dining hall, arriving there after one microsecond. From O'Connell bridge you just saw the clapper's hands coming together. At the dining hall, one microsecond later, the same image is just arriving. So, on your journey, you would see the clapper frozen in time. If you travelled just a bit slower than light, the image would have overtaken you slightly, so you'd see the clapper moving in extreme slow motion rather than frozen (and making a nonsense of the phrase "run like the clappers" ). The slower you move, the less the slow-motion effect, but there's always a bit of it -- even if you just move your hand away from your face, it moves very slightly in slow motion relative to your head.

That's what was happening with the Jupiter satellite measurement by Römer, mentioned above. As Jupiter moved away from us, the satellite was moving in slow motion and getting further and further behind the expected eclipse time.

jane82

Does it mean that the planets we are looking at as possible earth replacements may be completely different now to the light we are seeing?
Could there be a great wall of China there but we.wont see it for another few hundred years?

shruikan2553

jane82 wrote: »

Does it mean that the planets we are looking at as possible earth replacements may be completely different now to the light we are seeing?
Could there be a great wall of China there but we.wont see it for another few hundred years?

Yup, there could also be a planet somewhere that is seeing us as celts.

john the one

So if I could build a periscope that goes to Saturn and back, I could look at myself actually looking at myself in the past and future?

ps200306

john the one wrote: »

So if I could build a periscope that goes to Saturn and back, I could look at myself actually looking at myself in the past and future?

No, you can only look into the past, never into the future.

john the one

Yeah I was only trying to be a smart arse. Has to be a way of seeing into the future

ps200306

euser1984 wrote: »

Is einsteins space time related to this in anyway? Or theories about black holes?

Yes, the effects being described concerning motion are the "time dilation" aspect of Einstein's theory of Special Relativity. When Einstein formulated General Relativity, he realised that gravity causes similar effects. So time slows down near the surface of the earth compared to far away from it. The stronger the gravity, the stronger the effect, so someone clapping their hands at the boundary of a black hole would be seen by a further away observer as frozen in time, just like the effect I mentioned in the Spire example above where travelling away at the speed of light would result in a similar observation.

ps200306

john the one wrote: »

Yeah I was only trying to be a smart arse. Has to be a way of seeing into the future

We're all time travellers into the future. Just wait a while and you'll get there. :pac:
Can't see it in advance though, so can't help with next year's Cheltenham.

john the one

ps200306 wrote: »

We're all time travellers into the future. Just wait a while and you'll get there. :pac:
Can't see it in advance though, so can't help with next year's Cheltenham.

Hang on....what if I traveled for 50 years into space and back, at extremely high velocities, when I get back to earth, more that 50 years will have passed so technically I will come back in the future from my perspective.

dimcoin

euser1984 wrote: »

Someone was telling me that light takes about an hour or so to travel to earth from Saturn.

Does this mean if I am looking at it through a telescope, that I'm seeing something that happened an hour or so ago?

Thanks.

Think about this, when mars rovers send data back to earth, or a command is sent from earth to the rovers...it takes minutes each way for the data to move across the space between earth and mars.

ps200306

john the one wrote: »

Hang on....what if I traveled for 50 years into space and back, at extremely high velocities, when I get back to earth, more that 50 years will have passed so technically I will come back in the future from my perspective.

Not as such. if you bring a clock with you and keep an eye on it, you'll see that it just goes at the normal constant rate. So you're just travelling into the future at the same rate as you always do. When you get back, you'll find that everyone else has aged faster than you, though. So you'll be fifty years older but your pals will be older again.

Capt'n Midnight

john the one wrote: »

So if I could build a periscope that goes to Saturn and back, I could look at myself actually looking at myself in the past and future?

If you had a big enough mirror you could see yourself in the past. Except you need a good telescope because the photons spread out.


If you are 30cm from a mirror it will take light one nanosecond each way. So you see yourself 2ns ago. But your vision works at about 40ms and cognation may be over several seconds so not really practical.

PAL TV uses delay lines. Light (and sound) are encoded on a signal. At the receiver every second line is converted from electrical to sound and then put in a delay line that takes 64us (or whatever ) to travel across a quartz crystal and is then converted back to electrical signal. Weird stuff when you consider the technology available in early colour TV's.

Tordelback

This of course is the basis of one of the best bits of Flann O'Brien's The Third Policeman, where the philospher de Selby uses the "appreciable and calculable interval of time between the throwing by a man of a glance at his own face in a mirror and the registration of the reflected image in his eye" to view his younger self by employing two mirrors and a telescope. He observes himself (in increasingly tiny reflections) right back to the age of 12, after which point his efforts to go further back are frustrated by ‘the curvature of the earth and the limitations of the telescope.’

O'Brien was a true genius.

Hijpo

RebelButtMunch wrote: »

Nope. You see saturn ten mins ago. Unlesd someone on saturn had a mirror pointed at the sun. Then you would see the sun in the mirror as it was 94 mins ago

Ah, i figured we see saturn because the suns light illuminates it.

ps200306

Hijpo wrote: »

Ah, i figured we see saturn because the suns light illuminates it.

Yes but you are seeing light scattered off the surface of Saturn, not a coherent image of the sun. Otherwise you could say you are seeing the core of the sun from 100,000 years ago when you look at it, 'cos that's how long it takes photons on average to reach the surface after being bounced around inside after they are produced.

bombs away

What I cant understand is that the most distant galaxies we can see are 13 billion light years away give or take. So the light that we see is from just after the big bang right? But just after the big bang the observable universe was alot smaller than it is now. And the earth didn't even exist back then. So how come the light has taken over 13 billion years to reach us even though when it was sent intially the diameter of the total universe was alot smaller and this planet was'nt even around.

Probably not making a huge amount of sense with that but I can't get my head around it. The only way I can think of it happening is if the universe itself is expanding at a faster speed than the light within it. Is this what is happening?

euser1984

This is gone over my head now but I will say that my understanding of this thus far is: We constantly see the past through our eyes and the further we move away the more behind we can get. Just like watching someone hit a hammer from the distance - the sound we hear happened in the past.

When we look through a telescope and observe planets we see the past also. If there was alien life on Saturn and we had contact with them, they could ask us if 'said' made a mistake ten minutes ago and isn't admitting it and vice versa; we could say wait another five minutes until we can see it. The further we go distance wise, the more back in time we can go....

Capt'n Midnight

Nothing moves faster than light in a vacuum but right after the big bang the universe was full of expanding stuff, there still wasn't a vacuum.

So stuff could move faster than the speed of light in the stuff.

bombs away

whaaaaa

Mind blown

COYVB

Capt'n Midnight wrote: »

Nothing moves faster than light in a vacuum but right after the big bang the universe was full of expanding stuff, there still wasn't a vacuum.

So stuff could move faster than the speed of light in the stuff.

Also, if you have an area (the universe of stuff that came about after the big bang) expanding at just the speed of light in all directions, the speed that two opposite sides of the universe are traveling apart would be faster than the speed of light (double? or would it increase as the distance between the points gets larger?)

ps200306

Capt'n Midnight wrote: »

Nothing moves faster than light in a vacuum but right after the big bang the universe was full of expanding stuff, there still wasn't a vacuum.

So stuff could move faster than the speed of light in the stuff.

That's not quite right. The speed of light in a vacuum is the fastest anything can go, light or anything else. In a non-vacuum, the maximum speed is lower, e.g. light travels slower through air (99.97% of the vacuum speed) or water (75%) or glass (60%) or diamond (40%).

However, the "stuff" that was expanding after the Big Bang (and still is today) is space ... and there's no restriction on how fast that can expand even though there's a limit on how fast anything can travel through space. So different parts of space, along with the material embedded in it, were carried away from each other faster than light could travel between them in the early universe.
`

bombs away wrote: »

What I cant understand is that the most distant galaxies we can see are 13 billion light years away give or take. So the light that we see is from just after the big bang right? But just after the big bang the observable universe was alot smaller than it is now. And the earth didn't even exist back then. So how come the light has taken over 13 billion years to reach us even though when it was sent intially the diameter of the total universe was alot smaller and this planet was'nt even around.

Probably not making a huge amount of sense with that but I can't get my head around it. The only way I can think of it happening is if the universe itself is expanding at a faster speed than the light within it. Is this what is happening?

Yes, and this leaves us with an odd situation. In the extremely early universe, there was hot matter uniformly distributed, and light was produced everywhere throughout the universe. It couldn't get very far because it interacted with matter which also filled the universe, so the light was scattered in random directions. But after about 300,000 years, the matter in the universe had expanded and cooled sufficiently to become transparent, and the light was set free to travel in randomly oriented straight lines throughout the universe. It was -- and still is -- everywhere: we're embedded in it and it comes to us from all directions in the sky. This is the so-called cosmic microwave background radiation. Then there is the light from stars and galaxies that formed much later, when the expanding space had carried clumps of matter far apart. We see the light from these arriving from different epochs in the past depending on distance.

As you say, the universe was smaller then, and we do indeed see galaxies in a less evolved state than galaxies near us, and also tidally distorted by gravity because the galaxies were closer together and interacted more.

COYVB wrote: »

Also, if you have an area (the universe of stuff that came about after the big bang) expanding at just the speed of light in all directions, the speed that two opposite sides of the universe are traveling apart would be faster than the speed of light (double? or would it increase as the distance between the points gets larger?)

That's right -- it's possible for parts of the universe to be increasing in separation faster than the speed of light. However, although we sometimes talk about the recession speed, it's actually inaccurate to say that anything is travelling faster than light -- it's space that's expanding. The analogy is sometimes given of raisins in rising bread, or dots on a balloon that is being inflated: the raisins (or dots) are being carried away from each other by the space between them expanding, not because of any proper motion of their own. The more space in between, the faster they are carried apart. When light travels to us across long reaches of space, the expansion of space affects the light as it travels. It has the effect of stretching the light wave throughout it's journey, so that when it arrives to us its wavelength is longer (which, for light, means redder), a phenomenon called the cosmological red shift. The red shift of the galaxies is one of the primary pieces of evidence for the Big Bang.

syngindub

Is it true we can see the remnant's of the Big Bang from Static on tv?

Capt'n Midnight

syngindub wrote: »

Is it true we can see the remnant's of the Big Bang from Static on tv?

no.


well yes, but it's only a tiny fraction of static on the screen

on very old TV's most of the noise was generated internally to prevent a bright spot burning the screen if there was no signal

Standman

It's all such mind bending stuff! Is there an 'edge' of the universe, i.e. a point after which space ceases to exist?

ps200306

Standman wrote: »

It's all such mind bending stuff! Is there an 'edge' of the universe, i.e. a point after which space ceases to exist?

There's a number of different "edges" (all in theory ... we can't actually see any of them, although we're pushing the boundaries back with technology).

First of all, when we look out we are looking back in time. In principle we could look all the way back to the Big Bang, and this would be the ultimate "edge" of space and time.

In practice, the universe was full of a hot plasma until between 300 thousand and 400 thousand years after the Big Bang. Like the plasma that the sun and stars are made from, it was opaque to light. When it cleared (gradually, like a clearing fog) light was set free to travel the universe. So we can't see back any further than this (although for the reasons given later, we can't see this far either). This "edge" is commonly called the "last scattering surface". A common mistake is to think that this is where the cosmic microwave background comes from, since it represents the time at which the CMB was set free. But the CMB comes from all around us, reminding us that our spot in the universe, along with every other spot, were once squeezed together into a tiny volume.

Yet another "edge" is the one from which a ray of light which has been travelling toward us since the beginning of time would reach us. This could be called the edge of the observable universe, but the cosmologists use the fancy name of "the particle horizon". As you will realise, the particle horizon is not a fixed distance away -- new stuff is coming into view all the time as the universe gets older. The particle horizon is currently about 46 billion light years away.

One of the most astounding discoveries of the last two decades is that the rate of expansion of the universe slowed for ten billion years after the Big Bang under the force of gravity, but is now accelerating again due to "dark energy"! So, although new things are coming into view over the particle horizon, eventually this will stop happening, and in fact things will start to disappear again in future. So there is a maximum limiting distance that we will ever be able to see, and this "edge" is called the "cosmic event horizon". It's about 60 billion light years away.

So there you have it -- four "edges": the Big Bang itself, the last scattering surface, the particle horizon and the cosmic event horizon.

(Just in case you're wondering how we can see stuff 46 billion light years away when the universe is less than 14 billion years old ... well, it's complicated: unfortunately in an expanding universe there are multiple ways to measure distance none of which has an exclusive claim on being "right").

jacksie66

This post has been deleted.

orchidsrpretty

Can the universe be likened to being inside an ever expanding sphere? Is this why it said space is curved?

RebelButtMunch

Standman wrote: »

It's all such mind bending stuff! Is there an 'edge' of the universe, i.e. a point after which space ceases to exist?

Sometimes a question itself is not valid. For example. "What happens if your at the north pole and you go north?"

So maybe the idea of the universe having an 'edge' isn't a correct assumption. It's not easy to get your head around that.

ps200306

orchidsrpretty wrote: »

Can the universe be likened to being inside an ever expanding sphere? Is this why it said space is curved?

Not quite inside the expanding sphere -- this would imply a boundary surface that we could travel to in principle. It is probably better to think of the surface of an expanding balloon with dots on it that are moving away from each other as the rubber between them expands. In this analogy, the two-dimensional surface of the balloon represents 3-D space. Even if the surface is finite, so that you could travel around it, it has no boundary as such. There is no concept of "inside the balloon". All of space exists on the surface (a so-called hypersurface in the real world of 3-D space).

One implication is that if you could see far enough in opposite directions you'd be able to see the same stuff from opposite sides. (Remember that light is constrained to follow the surface of the cosmic balloon too). Scientists have looked for that in the CMB maps of the sky, but have found nothing. So if the universe is a hypersphere, the radius of curvature is bigger than the observable universe.

However, a hyperspherical geometry is only one possibility -- one with so-called positive curvature. It is also possible to have negative curvature, in which case the 2-D analogy would be a hyperbolic surface, shaped like a saddle (nowadays the analogy used more often is a Pringle :pac:) that curves away infinitely in all directions. In between these extremes there are more or less curved hypersurfaces, with the zero-curvature option being "flat". Positive, negative, and zero curvatures are associated with universes that will collapse in the future, or expand without limit, or will just coast along asymptotically -- expanding more and more slowly but never quite stopping. Or, at least that was the case when we thought everything was governed by the matter density of the universe and its curvature. Nowadays we also have dark energy to deal with. But that's another story. We now think we're in a universe that will expand forever, but the geometry seems extremely close to flat.

King George VI

RebelButtMunch wrote: »

Sometimes a question itself is not valid. For example. "What happens if your at the north pole and you go north?"

So maybe the idea of the universe having an 'edge' isn't a correct assumption. It's not easy to get your head around that.

There are two logical possibilities. I'm sure there are more that I'm not aware of but the ones I think make the most sense are:

1. The universe has an edge - a point where the universe just kinda stops.

2. It just goes on infinitely.

Either of those explanations seem equally ridiculous to me when trying to picture it.

Standman

ps200306 wrote: »

One of the most astounding discoveries of the last two decades is that the rate of expansion of the universe slowed for ten billion years after the Big Bang under the force of gravity, but is now accelerating again due to "dark energy"! So, although new things are coming into view over the particle horizon, eventually this will stop happening, and in fact things will start to disappear again in future. So there is a maximum limiting distance that we will ever be able to see, and this "edge" is called the "cosmic event horizon". It's about 60 billion light years away.

Wow! I had heard about dark energy accelerating the rate of expansion but thought that had been happening from the start! It makes it so much more intriguing that it would just suddenly start taking effect ~3 billion years ago for no apparent reason. Are there any theories as to what could have possibly brought dark energy into existence at that point in time?

Thanks for the lengthy reply by the way, all fascinating stuff!

Standman

St. Jimmy wrote: »

There are two logical possibilities.

1. The universe has an edge - a point where the universe just kinda stops.

2. It just goes on infinitely.

Either of those explanations seem equally ridiculous to me when trying to picture it.

Well it could be possible that if you keep going in a straight line you could end up back at your starting point in space. In this case it would be an infinite loop just like circumnavigating the globe. On earth, if you want to leave it you can't just keep going north, you have to go up. So possibly in space, if you want to go 'leave it', then you have to go in another direction that isn't up, down, forward, backward, etc. That would be impossible for three dimensional beings like us!

King George VI

Standman wrote: »

Well it could be possible that if you keep going in a straight line you could end up back at your starting point in space. In this case it would be an infinite loop just like circumnavigating the globe. On earth, if you want to leave it you can't just keep going north, you have to go up. So possibly in space, if you want to go 'leave it', then you have to go in another direction that isn't up, down, forward, backward, etc. That would be impossible for three dimensional beings like us!

I guess you're right. That's where a Stargate comes in handy.

ps200306

Standman wrote: »

Wow! I had heard about dark energy accelerating the rate of expansion but thought that had been happening from the start! It makes it so much more intriguing that it would just suddenly start taking effect ~3 billion years ago for no apparent reason. Are there any theories as to what could have possibly brought dark energy into existence at that point in time?

Thanks for the lengthy reply by the way, all fascinating stuff!

Well actually, you're right that it has always been around. But its influence relative to the matter and radiation density of the universe has been changing over time. If you can bear a bit of maths, the following connects all the important cosmological parameters (it's a Friedmann equation based on General Relativity and the Friedmann–Lemaître–Robertson–Walker metric for a homogeneous isotropic expanding universe :eek:, but that's not important right now ):



The above relates the "Hubble parameter" (the rate of change of the cosmic scale factor, effectively the rate of expansion) to the matter and radiation densities , the dark energy (), and the curvature k.

In the nice simple universe that Einstein supposed, where the dark energy (he used a different name for it) was zero and space was flat (i.e. k=0) then the expansion rate just depended on the matter and radiation density. This was called the Einstein-deSitter model. The expansion rate was high in the early universe when the density was high, and lower as the density falls off with the expansion of the universe. Whether or not the universe expanded forever would be solely determined by whether the matter density was above or below some critical density.

However, a non-zero dark energy component complicates things considerably, and leads to several possible different universes depending on the ratios of the matter, energy and dark energy densities and the curvature. It can give us a universe that expands rapidly, then slows, but then takes off again.

One way to picture this is that in the extremely early universe, radiation dominates and produces an expansion pressure. As the universe expands, it's volume goes up with the cube of the radius. So the matter density falls correspondingly. However, the radiation density is also affected by the cosmological red shift and thus falls with the fourth power of the radius ( - as well as photons being spread more thinly, each photon's energy is reduced by being redshifted). So, instead of being radiation dominated, the universe enters a matter-dominated phase where gravity is slowing down the expansion. But the matter density continues to fall, and if we have a dark energy which is proportional to the overall volume of space, it starts to take over as the universe gets bigger, so things begin to accelerate. We don't know what such a form of energy would be, but there is speculation about a "vacuum energy" produced by space itself. (Don't ask me, that's as much as I know ).

Zubeneschamali

ps200306 wrote: »

there is speculation about a "vacuum energy" produced by space itself.

Harnessing Vacuum Energy would be all very well, but I don't use the vacuum cleaner as much as I should, I'd prefer to harness Home Heating Energy (aka Diesel Energy)

Of course, we must avoid Red/Green Diesel Energy for cars.

Carawaystick

syngindub wrote: »

Is it true we can see the remnant's of the Big Bang from Static on tv?

sort of.
Two lads Penzias & Wilson were testing a radio back in the '60's and were still getting more noise than their calculations reckoned (noise ~= static on a tv)

turned out the excess noise was the cosmic background radiation
and the two lads got a nice trip to Stockholm for a Nobel prize

Most of the static (or hiss on a radio) is noise generated by the electronics in the tv/radio itself, followed by noise generated by other electrical things in your house.

Capt'n Midnight

Zubeneschamali wrote: »

Harnessing Vacuum Energy would be all very well, but I don't use the vacuum cleaner as much as I should,

there isn't much energy in a vacuum and Maxwells deamon doesn't work when the gradient builds up so meh.

we have lots of solar though and a big enough rectanna matrix would enable you harvest the cosmic background

ps200306

Zubeneschamali wrote: »

Harnessing Vacuum Energy would be all very well, but I don't use the vacuum cleaner as much as I should...

So if you hear a big sucking sound, you'll know it's the end of the universe, and not your house being cleaned.

Actually, I believe it's going to be a big ripping sound ... there's one theory that the runaway expansion due to dark energy will first accelerate all the galaxies out of our observable universe, but eventually the galaxy will start coming apart too, and then stars and planets, and eventually the individual atoms as even the intra-atomic forces are finally overwhelmed. It's called, appropriately, the Big Rip:

"About 60 million years before the end, gravity would be too weak to hold the Milky Way and other individual galaxies together. Approximately three months before the end, the solar system... would be gravitationally unbound. In the last minutes, stars and planets would be torn apart, and an instant before the end, atoms would be destroyed."

ps200306

Capt'n Midnight wrote: »

...a big enough rectanna matrix would enable you harvest the cosmic background

REALLY?
I've never heard of such a thing, and know less than nothing about it, but I'm thinking -- on thermodynamic principles alone -- harvesting energy from something at three degrees above absolute zero would need a cold sink that's even colder than that, which is next to impossible to come by for free in a universe which is all at the same three degree temperature. I know we're talking about a black body temperature of EM radiation here, but still .... !

TheMilkyPirate

This thread has melted my head.

Zubeneschamali

ps200306 wrote: »

REALLY? ... !

No, that was a joke.

But the bit about Hoovers...