Effects of a different CMBR temperature?
 

Greetings, all!

I'm curious: what would be the implication of a setting having the Cosmic Microwave Background Radiation temperature higher than in ours? Currently I'm mostly see differences in calculating blackbody temperatures of everything, and in detection modifiers for objects in space, but what would those changes be, based on a given new value of the temperature?

What other consequences would it have? Would a gradual or sudden change produce results significantly different from it 'always being that way' throughout the aeons?

Thanks in advance!

Re: Effects of a different CMBR temperature?
 

If it's a small different then there likely wouldn't be much of a change. The universe has been consistently expanding for billions of years, this expansion leads to the gradual reduction of the CMB temperature. This is because the energy density of radiation is inversely proportional to the scale of the universe raised to the fourth power, thanks to the effects of volume and wavelength - increasing wavelength decreases frequency, whic decreases the energy of radiation.

As I said before, the universe has been expanding for a long time, really very quickly. The current rate of expansion is about 70 kilometers per second per megaparsec, so if you look at a galaxy a million parsecs away it seems to be moving away at 70 kilometers per second, if you look two million parsecs away, it's 140 kilometers per second, etc. So the universe is considerably bigger now than a few billion years ago, and energy density - and thus temperature - goes down very quickly with increasing scale, yet when we look back at the earlier universe - which we can literally do thanks to light travel-times - it looks much the same as the universe nowadays.

In short, a higher CMB temperature wouldn't produce much of an effect, unless you're talking about a rather more extreme increase than I think. In which case, I'd need some time to think it over.

Re: Effects of a different CMBR temperature?
 

What do you count as a little, and what is (the beginning of) extreme, and what would be the sensor modifier effects of the former and the latter?

Re: Effects of a different CMBR temperature?
 

Use Wein's Law to figure out where the peak wavelength is. If it's not very close to or within a band where you're detecting things, then it probably won't matter much.

The intensity is going to scale as T^4, which is a lot -- but, even still, it's not very bright right now. Remember that to detect it, we have to use balloon-borne or space-based experiments, and even then there's a lot of other background and such to subtract.

What kinds of things are you trying to detect? With an example, I could probably give a back-of-the-napkin estimate of how much hotter the CMB would need to be for it to make a difference.

Also, it wouldn't change how we calculate blackbodies. The CMB may be our most perfect example of a blackbody, but the constants used (k and h) are measured in other places. I have a vague memory of the ultimate calibration of blackbodies coming from an experiment done at some observatory with molten platinum....

Re: Effects of a different CMBR temperature?
 

Generally I'd put it at at least half the effective temperature of the thing you are trying to detect to have any effect at all - at that point it's still radiating only 1/16th as much per unit area (and mostly not even at the same frequencies). A sensor so lousy it can't pick out something 16 times brighter than the background with no frequency discrimination at all is worthless junk.

That's about where it matters for blackbody temperatures too, adding back 1/16th the energy you are radiating away raises your (kelvin) temperature 1.53%

Re: Effects of a different CMBR temperature?
 

So if Malloyd thinks you've got to get up half of a human-crewed spaceships 270 K to make a difference that far beyond the boiling point of hydrogen and I'm not sure even gas giants exist. Icey bodies almost certainly won't.

As to the cosmological implications I think the universe has to be a lot smaller and younger. The initial temp of the background radiation is fixed by the laws of physics. You don't get the "Big Bang" flash until space has cleared out enough for the photons to fly between the electrons and protons without being absorbed. That sets things to happen at a given density so making the universe have more mass wouldn't change it.

So there probably hasn't been enough time for third generation stars to appear and planets to cool and life to evolve.

So unless the universe's physics are radically different I don't think any beings similar to ourselves would ever face such a problem.

Re: Effects of a different CMBR temperature?
 

Well, the temperature of the CMB is directly related to the expansion of the universe, so you can just look at what the universe looked like when it was younger. If you don't want a younger universe you probably have to change dark energy or something.
Unless you're scanning at microwave wavelengths, changes in the CMB will not directly affect detection at all. However, differences in the expansion of the universe probably mean there's also changes in the backgrounds of galaxies, which will have some effect.

Re: Effects of a different CMBR temperature?
 

Seems like there would be some changes on the cosmic scale of things with galaxy clusters being closer to each other, but...

Very few changes in the mundane minutia that most games would happen in. At most, you'd see faster intergalactic travel, but since most of that happens at the speed of plot anyway....

Re: Effects of a different CMBR temperature?
 

IOW, even if you raise it to 30K or even 100K, this will have zero noticeable effect on planetary climates?


Will it have any effect on the 'space is very cold' factor of detection under any circumstances (such as ways of radiating away waste energy in an adjusted spectrum, perhaps with some ultra-tech advancements)? Or none either?

Re: Effects of a different CMBR temperature?
 

Doing the most simplistic calculation - age of universe/(ln(270/2)/ln(2.7)) - you'd expect that temperature about 470 million years after the beginning. That is slightly after stars have started to form, but not by very much. Which makes sense, stars presumably won't form until it's cooler than their surface temperatures, and on an exponential curve stars are not actually a lot hotter than 270K.

Re: Effects of a different CMBR temperature?
 

Well for terrestrial planets. It may matter for iceballs. It's much the same issue as the second stars of binary systems usually don't matter for the habitable planet's temperature.

Two temperature sources add as the fourth root of the sum of their fourth power. So if you have two sources that would heat something to 100K in isolation, their combination heats the thing to 119K, which could matter, but if you have a one source that heats it to 300K and add another that would heat it to 100K, the combination heats it to 300.9K, which is likely negligible.

Edit: Is there a goal here? If you want a setting where space happens to be warm, I wouldn't suggest tampering with cosmology. Look for an excuse to bathe the entire region of the setting in a hot gas cloud instead. Yeah it's a little tricky to justify why whatever heated a cloud light-years across didn't kill everything in the region, but you can probably come up with something. If another galaxy collided with the Milky Way you might be able to get a jet of gas getting tossed off in the direction of one of the Magellanic Clouds that would still be fairly warm when it got there with less handwaving than changing the expansion of the universe. Sure it'll pass through, or cool back down again in 10 or 100 million years, but your metaplot doesn't need that much time anyway, right?

Re: Effects of a different CMBR temperature?
 

30K may prevent the formation of planetary systems; 100K almost certainly will. Upper limit for having planets that support life is probably a CMBR temperature of 6-8K due to age of the universe effects. However, if somehow we teleport a planetary system into a location with a different CMBR, a 100K background would increase the temperature of a habitable planet by about 1.5 degrees kelvin.
If it's high enough it will cause increased background noise, but for the most part thermal emissions will be at wavelengths where the CMBR is dim. If your goal is to make detection in space harder, I wouldn't mess with the CMBR, just increase zodiacal dust by a lot. Or add an asteroid belt (blowing up Mars and/or Venus would accomplish both objectives).

Re: Effects of a different CMBR temperature?
 

I'm contemplating possible weird alternate universes or areas of weird physics, but decreased detection ranges are something that I consider a nice thing to look into at every opportunitly.

So speaking of such dust . . . how much can it be 'safely' increased, and how much of an effect can that produce on detection modifiers?

Re: Effects of a different CMBR temperature?
 

What's the physics of that? A lot of planets in our solar system seem to have formed where the blackbody temperature based on solar radiation is higher than either of those figures.

Re: Effects of a different CMBR temperature?
 

The temperature of a molecular cloud is one factor that inhibits collapse, which in turn prevents star formation. I haven't been able to find any firm numbers on this, though. However, if your cosmic background radiation is hot enough, it might prevent or at least slow down star formation.

Re: Effects of a different CMBR temperature?
 

It's based on Jeans instability, and works out to the minimum mass of a gas cloud that can collapse scaling with T^3/2. As such, a high temperature results in massive gas clouds collapsing into massive stars that burn themselves out in short order.

Re: Effects of a different CMBR temperature?
 

Oh, okay. Do we know the minimum mass in our universe, as a function of cosmic temperature back around 5,000,000,000 years BP?

Re: Effects of a different CMBR temperature?
 

Far as I can tell from brief research, not significantly different from now, gas clouds drop to around 10K and you have to go back 10+ billion years for the CMB to be hotter than that.

Re: Effects of a different CMBR temperature?
 

That's partially helpful, but I was looking for a lower limit on the mass of a stellar system, either in kg or in multiples of our sun's mass. If I have one lower limit and one temperature I can figure out other lower mass limits for other temperatures, but I need one starting point. Is there any estimate of how small a "star" could be at the time when our solar system was formed?

Re: Effects of a different CMBR temperature?
 

Ah, so we're talking about extreme values for the CMB temperature. That could probably be achieved by modifying the cosmological constants, i.e. tweaking the distributions of matter, radiation, and dark energy. A higher radiation density (for more energy) and a lower matter density (for less absorbing material at the big bang) might do the trick without radically altering things. At the moment the radiation energy density is negligible compared to the other constants, increasing it slightly shouldn't have much effect on the evolution of the universe (i.e. expansion and possible contraction).

From my understanding between 10K and 20K is the temperature when stars begin to form. So as Anthony said, you could probably get away with a CMB temperature of 6-8K before it increased the temperature of the clouds too much (the low temperatures are required for the clouds to reach sufficient densities). That's around triple what it currently is. Note however that because of the way temperature drops as the universe expands, an 8K CMB universe won't have been suitable for star formation for very long at all, even if it's a similar scale to our universe, in a lot of ways it'll look like our universe a long time in the past.

Re: Effects of a different CMBR temperature?
 

It's when current generation stars form. First generation stars formed at higher temperatures, but you're not going to get planetary systems around first generation stars.

Re: Effects of a different CMBR temperature?
 

In addition, planets around first generation stars would be hydrogen and helium only.

Re: Effects of a different CMBR temperature?
 

It wasn't molten platinum, if I remember my freshman physics correctly. It was a hollow cavity inside a solid block of platinum. You need it to be a hollow cavity to make the effects of albedo irrelevant. Checking Halliday and Resnick, I see they say it also makes the size and shape of the cavity irrelevant.

Re: Effects of a different CMBR temperature?
 

So, okay, on one hand, mean energy per unit volume varies as L^(-4). On the other hand, minimum mass for gravitational collapse to form a solar system varies as T^(3/2). To link the two, we need a conversion between energy and temperature.

* In basic thermo, temperature was defined as mean molecular kinetic energy, which would suggest that T is proportional to E, probably using Boltzmann's constant or the ideal gas constant.

* In blackbody radiation, energy radiated per unit time is proportional to T^4.

* However, the universe doesn't seem to be radiating into anything other than itself. I believe the proportionality for energy *content* in a medium is that internal radiation is proportional to T^3.

Which of these gives the right scaling relationship?

Re: Effects of a different CMBR temperature?
 

The first stars formed when the universe was about 200 million years after the Big Bang. How hot would the CMB be then.