h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

The whole point of the paradox is that the assumptions are shown to be wrong!!!

To question the validity of the assumptions says nothing about the validity of the paradox. It is a paradox because the assumptions seem perfectly reasonable (you give no reasonable excuse as to why the universe cannot be assumed to be infinite - 'we are towards the edge of a galaxy that is away from the centre of the universe' is not a counter argument in the slightest), but they are in fact incorrect.

me[Andy]g

That is not what I said. I will be adding more to this entry to explain my point.
Not only are the assumptions wrong, so are the conclusions.

Alji

You show me where you have explained fully the problems with the assumptions and conclusions, and I will read it.

me[Andy]g

Alji, a question -

Do you mean to say that the assumptions are 'wrong' or that the assumptions are 'not reasonable'?

me[Andy]g

I'm still working on it but I do believe the assumptions are wrong.
One of the main conclusions states;
'Currently, the finite age solution of the paradox is preferred because it supports Big Bang theory, which says that the universe started a few billion years ago, and has been expanding ever since. This alone (with a contribution from the expanding universe explanation) is enough to account for the sky being as dark as it is.'

But if the assumptions are wrong so are the conclusions.
For example, is this true?
'absorbing dust would eventually come to equilibrium, and emit as much radiation as it absorbed'
If it is, then why is that the interstellar dust in the spiral arms of the Milky Way, is dark enough to obliterate the central hub which is millions of times brighter than the rest of the galaxy.

Alji

This is where the problem is.

Assumptions are *not* "wrong" or "right", they are *assumptions* that need to be verified as being "true" or "false". There is a distinction between "right and wrong" and "true and false". The conclusions are exactly the verification of whether the assumptions are true or false. In Olbers' paradox, the only conclusion is that the assumptions are false. If you want to start talking about Big Bang Theory, then that is a different matter altogether.

me[Andy]g

Wrong -

Not according to truth; not conforming to fact or intent; not right; mistaken; erroneous; as, a wrong statement.

Not in conformity with fact or truth; incorrect or erroneous.

<quote>
Currently, the finite age solution of the paradox is preferred because it supports Big Bang theory, which says that the universe started a few billion years ago, and has been expanding ever since. This alone (with a contribution from the expanding universe explanation) is enough to account for the sky being as dark as it is.


Alji

I still don't get you. The passage you quote is perfectly correct AT THE CURRENT TIME, as it says.

As I said before, if you disagree with Big Bang Theory, that's a different matter. But scientists who believe that the universe has always been here are few and far between, hence the conclusion from Olbers' paradox that the universe is finite in age is correct at the current time.

Science will no doubt change and adapt and one day we may be able to show whether the conclusion we currently reach from the paradox is true. But right now, there are no viable alternatives whatsoever that can be backed up by accepted science.

me[Andy]g

> "absorbing dust would eventually come to equilibrium, and emit as much radiation as it absorbed"

Key-word: eventually. The absorbing dust in the milky way is not yet at equilibrium, and absorbs more than it emits.

Olber's paradox supports many theories, including creationism (which says the universe is only a few thousand years old).

Rayleigh and Jeans, around 1900, calculated that all the electromagnetic energy would be sucked up by a field without limit but actual observation by Planck showed that the distribution of energy falls off to zoro as the frequencies increase (this is now called the Planck Radiation Law). This was the beginning of Quantum Theory.
All the radiation is re-radiated but not at all frequencies. Most will be in the infra-red.

Alji

> All the radiation is re-radiated but not at all frequencies. Most will be in the infra-red.

Right. So *if* there is an infinite amount of radiation "sucked up by a field without limit", then there will be an infinite amount re-radiated in the infra-red frequencies. (e.g. say 80 percent is infra-red, then 0.8 times infinity is, er, infinity)....

By the same argument... anything re-radiated in any visible frequency will also be infinite. a/100 * infinity = infinity, where a is the percentage of visible re-radiated. It is a fraction of the original amount of radiation, but it is still infinite. You cannot have a finite fraction of an infinite amount... or, put another way, you cannot divide infinity by any non-zero finite number and get a finite number.

me[Andy]g

Non of the radiation will be in the visible spectrum.

I have been thinking up a list of ways the energy could be used up.

1........If E=MC2 then M=E/C2 (or M=C2/E).
2........Low entropy, high frequency radiation -> high entropy, low frequency radiation.
3........Quantum fluctuations.
4........Galactic matter of an unknown nature. This material has been observed only on one of the 100-micrometer IRAS scans.
5........"Blank fields." IRAS scans have found infrared sources where no visible object exist.

Alji

So, any matter or field in the universe which destroys or captures energy, if in sufficient quantities and distribution, solves Olber's Paradox. Can we agree on that?

No. Not if there's an infinite amount in the first place. Which there will be *if* the universe is infinite in space and time - the assumptions of the paradox.

Plus energy cannot be "destroyed" - energy is always conserved.

So you make sure that your 'absorbing dust' consumes an infinite amount of energy. This is easy to do, because there's an infinite amount of it, and it's been running for an infinite amount of time.

> "Plus energy cannot be "destroyed" - energy is always conserved"

That's just a theory. Plus it's entirely possible for this absorbing dust to convert the light energy into something else - mass for example.

The Horsehead Nebular, The Coalsack and many others show exactly how opaque to visible light the interstellar dust can be.

As far as heating goes, the visible spectrum is not at all hot - Switch on a light bulb for a few minutes and the bulb gets hot - Switch it off and the room is dark but the bulb is too hot to hold.
It is not the light that is heating the bulb but the IR radiation and the convection of heat from the element as the electrons heat up the coil and energy is converted from one form to another.

We do not go brown in the sun as a result of burning, - UV is cold and a thin smear of sun cream can protect us from the harmfull radiation. Glass is opaque to UV.

In an infinite universe with galaxies all around at varius stages in their evolution there must be as many dead galaxies as bright ones. Some of these 'GHOST GALAXIES' have been detected.

Alji

Hi Alji, I have found you with a very interesting problem on hand!
Have you given up? It has passed some time since the last posting...
I have read the massive exchange of messages both on this page and the original one, and it seems to me that essential points that could clear up the matter were not touched. I will try to address them.
Any chunk of matter loses energy all the time. How much energy is lost is determined by its temperature. Temperature also determines at which wavelenghts this energy will show up.
For objects at 100 K or less, energy will be radiated as radio waves.
For objects at 300-1000 K, it will come out as infrared radiation. That is why infrared sensors can know when we are near and open the doors.
For 4000-20000 K, energy will take the form of visible light. This is the temperature of stars. It is also the temperature of lamp coils, and that is why they emitt visible light.
For higher temperatures, we will have Ultraviolet, X-rays, or even gamma-rays.
So if you heat up anything, it will radiate more, and in more energetic wavelenghts. This is why the existence of dust cannot explain why the sky is dark, as given enough time (billions of years), it would be heated to the point of being destroyed.
Our sensation of "heat" is tied to our sensors. Our skin has sensors for infrared radiation, which we interpret as "heat". UV radiation is not detected by those sensors, and by so do not produce the sensation of "heating", though it can damage our cells.
The same is true for our vision. Our eyes can detect only that part of the spectrum we call "visible light". Though bees can see UV.

My takes on the Olbers' paradox:

1) There is gas and dust in between the stars, that absorb or
scatter the light, reducing the number of stars visible in/at any
given point. But, given enough time, this gas and dust will be heated
to high temperatures, and it will emitt light also... What is enough
time? It is connected to the ammount of dust and the size of the
Universe. The bigger they are, the most time it will take.
2) Stars are not points, actually, so they are effectively blocking
the observer's view from very distant objects. As before, given enough
time, the photons would fill the Universe homogeneously...
3) As shown before, the Universe must not have been given enough
time to turn the sky ablaze, so we must find a way to guarantee that.
If the Universe is not infinite in time, i. e., it has a definite
begginning, not very far in the past, that condition is satisfied -->
the Big Bang theory! Some people regard this solution as a cornerstone
of the Big Bang model. I do not see it this way, though, and in that
point I disagree with the vast majority of astronomers. There are two
loopholes in this approach: (a) If the Universe is expanding with
accelleration, as the data from Supernova observations seems to show,
then it can be expanding faster than the light can fill it or heat
the dust; (b) In the quasi-stationary model, from late Sir Fred
Hoyle, new matter is created (increasing the absortion and scattering
of light), and the Universe expands faster than the light can fill it.
Marcelo Allen

Have I given up? No but I think every one else did because O. P. got into the Edited Guide!

>Any chunk of matter loses energy all the time. How much energy is lost is determined by its temperature. Temperature also determines at which wavelenghts this energy will show up.
>>-------> Size is also a factor and the ambient temperature will affect the rate of loss. The vacuum of space stops convection so radiation is the only means of heat loss or heat gain.

>For 4000-20000 K, energy will take the form of visible light. This is the temperature of stars. It is also the temperature of lamp coils, and that is why they emitt visible light.
>>------->Have you ever tried boiling water with a 1000 watt light bulb.
During the mid 1960's I was working with carbon arc lamps. These were used as a source of uv. The tip of the carbon rod reaches 3600 degrees C and the light is too bright to look at. This was used to illuminate a frame, one metre from the arc for 15 to 20 minutes.How hot do you think the frame was after 20 minutes?

>So if you heat up anything, it will radiate more, and in more energetic wavelenghts.>>-------> See Quantum phisics (Max PlancK Black Body Radiation @ http://www.phys.virginia.edu/classes/252/black_body_radiation.html

Here is a thought experiment for you;
You are sitting in a room which has mirrors all around you. In the middle of the room is a bright light. When you switch off the light where do all the photons go?

Alji (Member of The Guild of Wizards @ U197895)

That OP page is good enough to the guide, in my opinion. In fact, it is not clear to me where exactly lies your disagreement, and it seems nobody else could understand your arguments. It seems to me you have a difficulty to express yourself in a direct way, and people get bored. I felt this again when answering your message. For example, you asked me about the boiling water and the frame. You could cut up that and go directly to the result, because if I answer "no", you will have to give me the result, and if I say "yes", you still will have to interpret my observations. Can you see this? Maybe you should state the Paradox in your own terms, and how you propose it should be solved. Or you do not think there is a paradox at all?
As you can see on that very good page about blackbody radiation, the radiation power scales as T^4, so small differences in temperature can compensate larger differences in size. I was talking exactly about blackbody radiation, as you pointed we do not expect convection plays a role in space. The ambient temperature influences the flux of energy, but we are talking about dust in space. The temperature of space can be considered as 0 everywhere, so it can be disregarded.
No, I never tried to boil water with a lamp. Did you?
And what is the relation to the topic in discussion?
Your frame experiment: I would expect something one meter away from a lamp to be at the ambient temperature, even after hours of illumination. The frame would only heat up if enough energy is absorbed, and absorption is a somewhat complicated function of radiation wawelenght and composition of matter. For example, metals in general are good reflectors of visible and near infrared light, the main products of a lamp.
The mirror room experiment: when you switch off the light, the photons go to the same place they were alredy going. They are absorbed by the mirrors, as the earlier photons were. But I do not understand the reason for this trivial question. Photons have only 3 options when they interact with matter: absorption, reflection or transmission. Since mirrors are very good reflectors of visible light, and terrible transmitters, most photons will bounce from one mirror to the other until being eventually absorbed. How this enlights our discussion?