As already said several times in this blog, dark matter consists in an appealing option to reconcile predictions with cosmological data. Consequently, there are numerous searches for dark matter, and new ideas are regularly proposed.
[image credits: @pab.ink]
Very recently, my attention got triggered by a new scientific article in which it was considered to scrutinise Earth to probe dark matter.
In a few words, Earth has the possibility to capture dark matter, which could then annihilate and release energy within the core of the planet. The heat output (or the increase of the temperature on the planet) cannot however exceed the observations.
Dark matter and its interactions - the classics
Whilst dark matter is highly evidenced by data, it still escapes direct detection.
[image credits: SLAC]
The principle behind these direct detection experiments is quite simple (see the image).
First, one needs to build a large detector. Dark matter rarely interacting with matter, the detection volume needs to be maximised to have a chance to see something.
Second, the detector has to be buried deep underground, to be protected from the backgrounds (cosmic rays, human activities, etc.).
Monitoring what is going on, physicists then track events in which dark matter particles (being part of the dark matter wind blowing on Earth) would hit the detector constituents and generate a recordable recoil.
However, the story is not always that simple…
Captures and annihilations on Earth
There are models in which dark matter will interact with the crust of the planet before reaching the detector (that is buried underground). Its kinetic energy getting subsequently reduced, dark matter is then not able to generate any visible recoil in the experiments.
[image credits: NASA]
This could sound dramatic as we could be insensitive to several dark matter models.
There is however a way out!
The velocity of the dark matter particles decreases, so that dark matter particles could get captured by the planet (due to gravity). The dark matter density inside Earth hence increases.
This increase in density implies that dark matter could annihilate efficiently within the planet.
This results in a potentially significant heat output, that contributes to rising the temperature on Earth.
Dark matter vs. the planet temperature
In this article, the dark matter contribution to the heat output of Earth has been calculated, the results depending on various dark matter properties. On the other hand, we know that Earth generates about 47 TW of energy.
We can therefore constrain the dark matter interaction rate (the y-axis in the figure below). For a given dark matter mass (the x-axis on the figure below, 1 GeV being the proton mass), this rate must be such that the total energy output of the planet does not exceed the observations.
[image credits: arxiv]
The two grey areas corresponds to constraints stemming from the properties of the fossil radiation left over from the Big Bang (upper area), and from the underground experiments described above (lower area).
The blue area corresponds to setups generating a too large heat output. We can notice that this new method nicely fills holes in the dark matter search program.
Finally, the red contour is obtained by trading Earth for Mars (which generates at most 3.5 TW of energy).
Take-home message: Earth and dark matter
Earth gets a constant wind of dark matter that goes through the planet. Losing energy in the process, dark matter is slowed down and could be captured through gravity. Such captured dark matter could then annihilate within the planet, and generate an energy flux capable to rise its temperature.
Combining predictions with observations on the heat output of Earth, we get a new handle to discover dark matter, that is actually complementary to other existing dark matter probes.
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lol that picture!
hm... how much energy is "produced" by all the particles that Earth absorbs inside (not athmosphere or ground)?
All those that nearly never get caught, like Neutrinos.
@pab.ink is definitely the best of the best. I usually don't post anything without an image from him :)
Note that if something escape without releasing energy, then it does not contribute to heating the planet.
What we actually know the sum of all contributions: the total heat flow is measured (those are the 47 TW I mentioned in the post). For the different components to it, I didn't find much particle physics information. The main contribution is coming from the mantle of the planet and there are only models explaining the phenomena.
For the neutrino side, I have actually found this non open-access article. It says that studying neutrino physics could allow to explain the observed flux of 50 TW. The neutrinos are indeed remnants of what is going on inside.
I hope you are sharing these pictures with your son. I can imagine that he finds them hilarious. This one would get a vote from me even if there was no blog attached:)
The Take Home Message really helped. If I understand you correctly, the heat generated by dark matter (if that does happen) should be consistent.
If that's true, then Greta can relax. Alarm over global warming addresses the rate at which the planet is warming. That has to involve other, less consistent factors--like the Industrial Revolution and fossil fuel consumption. So, climate change still is a human-mediated issue, and not a cosmic inevitability (maybe?).
Well, anyway, you see I have no problem speculating. I love these forays into the possible but not known. The pictures really spice it up.
Both my sons have seen the picture before the post came out. They enjoyed it, especially the big one (that is currently extremely concern with climate change and environnemental issues).
Exactly: dark matter cannot generate more heat than observed.
However, this has nothing to do with the wind of dark matter. We know the distribution of dark matter in the Milky Way, and the solar system moves in the Milky Way. This is where the wind comes from.
The entire point of the post is that... this has nothing to do with global warming. The latter is connected to many parameters, one of them being the planet outgoing heat flow. Here, we take this heat flow as measured, and we make sure the dark matter contribution to it is small enough. Therefore, there is absolutely no way this would change anything to the climate change affair (since the heat flow parameter is not modified, otherwise the dark matter model is ruled out since contradicting data).
I hope this clarifies a little bit. Please let me know!
I think I do understand...as much as I can understand particle physics. Thank you! Fascinating.
I didn't realize you had two children. I was sure they would love pictures :)
I have even more secrets :D
Kind of far fetched but still interesting enough to give it some food for thought. Not sure if I even understood it all correctly but you mean to tell that dark matter can get captured by earths gravity that then would make the dark matter emulate energy=heat by "destroying" itself?
If it were to be true then we would be fucked either way I guess, since there's no way to prevent that from happening - wouldn't that be great news for the politicians lol.
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The amount of energy the Earth catches this way is far lower than get send out into space again, so no help for the politicians here, they still have to do something ;)
We still have to do something (i.e. take care of our planet no matter what). Not only the politicians (or things will probably never change).
Note that this is my opinion and I have not defined what the something is (this would be a good discussion to happen live, IMO).
Thanks for passing by. This is a very interesting comment and this means I should clarify a few things.
First, dark matter is assumed to interact with normal matter. This implies that:
This is the sum of these two processes that actually dictates the amount of dark matter that is left over today. At present time, dark matter is too diluted and the universe is too cold to have any of these two processes in action.
Let’s now go closer to the topic. Dark matter annihilation consists in the process number 2. For this process to happen, we thus need a pair of dark matter particles, which is not realised at present time except if the dark matter density locally increases by one way or the other.
Earth capturing dark matter concretises this increase in density, so that dark matter annihilation can take place: two dark matter particles can meet each other and produce normal matter. This normal matter contributes to the heat flow originating from the planet.
The Earth heat flow is however measured. We have a result, that comes with an error bar. Therefore, we must make sure that the dark matter component to the heat flow fits within the error bar. This allows us to constrain specific classes of dark matter setups (but not all of them). The interesting point is that this constrains models that were allowed by data so far. Thanks to this “Earth heat flow” technique, those models are now excluded.
is this clearer? If not, please do not hesitate to ask for more clarifications.
This is happening no matter what (once we agreed on the theoretical dark matter model to put in). The model is however such that dark matter does not generate any extra heating: the dark matter contribution has to fit within the observed heating.
Consequently, this won’t change anything for the climate. Actually, this post has nothing to do with climate change (I have just found it funny to correlate them. I know, my sense of humour sucks… ;) ).
I suppose there are more far-fetched theories out there but what would cause the annihilation of the dark matter which raises the temperature?
In most dark matter models, there exists a (non-gravitational) connection between dark matter and normal matter. This allows two phenomena:
The two processes are actually the inverse of each other and both are playing a big role to explain what is going on in the early days of the universe.
Today, the universe has expanded and cooled down. Therefore, dark matter is too diluted for the process #2 to happen and the Standard Model particles are not energetic enough to produce dark matter (and the process #1 is switched of too).
In the model discussed in this post, dark matter capture by Earth offers a chance to the second process to restart (we have enough dark matter in a small volume so that they can meet and annihilate again). This generates a flux of Standard Model particles that contribute to the heat flow of the planet.
On different grounds, the heat flow of the planet is very well measured: 47 TW (at the 5% level). This means, dark matter could contribute to these 47 TW (assuming that the details of the dark matter model are such that all of what I detailed in the post could happen; this is indeed a model dependent thing). In both cases (dark matter contributions to the 47 TW or not), the 47 TW are still 47 TW. Therefore, if it has an impact on the temperature changes, this impact is already accounted for by the climate models (who do not care about how the 47 TW arise).
Does it clarify? Sorry for the very long answer ;)
It does a little bit. Are we assuming the annihilation of the two particles is spontaneous?
Yes, this is definitely prompt.
Woa! This is a thought provoking post @lemouth :)
The question I have might not even be relevant to the study itself. But, I am going to ask away anyway: If dark matter annihilation indeed contributes to the rise of Earth's temperature, in what ways men could interfere with this in order to slow down global warming?
The illustration is awesome ! :D
The post is actually not provocative at all. It is state-of-the-art science. But to say the truth, I agree the title of the post and the first image are provocative (and funny too, aren't they?) :)
One must be careful on what is the cause what is the consequence here.
First of all, there is a heat flow outgoing from the planet. It is well measured: 47 TW (with an uncertainty of about 5% on the number). This measured quantity is included in the climate models that deal, among others, with the global temperature no the planet. Therefore, dark matter can or can't contribute to the 47 TW. This will always be 47 TW (it is measured).
Next, let's take a dark matter model. Sometimes, there is a contribution to the heat flow of the planet (the 47 TW), sometimes not. When such a contribution exists, it must be calculated and one must verify that it does not challenge the 47 TW measurement. If it is the case, the model is just excluded.
Therefore, this model has no influence on climate changes at all. It can contribute to one parameter of the climate models, that is taken as a measured value anyways.
Is this clearer?
I see, I see ... Thank you @lemouth, for taking the time to make this clear. Despite not having fully grasped it, I found this post particularly interesting. But, now I feel I have a better understanding of it, which made it all the more fascinating.
Yes! The illustration is incredibly witty :D I love it!
Wish you and the family a great weekend ahead! <3
Thanks for the wishes, although it is already Tuesday (I spent the week-end to travel to China). I hope you had a nice week-end too, and please do not hesitate to come back to me if needed :)
Well sure, but this would just be included in the known amount of heat released from the core, which has remained constant over the past 50 years.
While it may be a contributor to overall planetary heat release, the warming phenomenon is still caused by an increasingly insulating atmosphere, as seen by decreasing planetary energy loss, especially with wavelengths corresponding to CO2 absorbtion.
Great to see you around! :)
I totally agree. This is in fact the entire point of the post. We know the amount of heat released by the planet, up to some error bars (we approach the 5% accuracy). Then, if one constructs a dark matter model, we must make sure the dark matter contribution fits within the error bar. This is where the contraints shown on the last figure come from.
The warming is actually totally unrelated to the mechanism depicted in the post. This contrast with the title and the first image, I know (but they are funny, aren't they?).
As said above, we just discuss to one potential subdominant component of the heat flow of the planet. I insist on the word "potential", as this is model dependent. In some dark matter model, this is relevant. However, this component can roughly to 5% at most of the total amount of generated heat. This is what particle physicists must pay attention to when building a dark matter model.
The consequences of dark matter on global warming are then exactly zero (as you said), as dark matter will only contribute to a specific parameter whose value is unchanged no matter what. This does not affect any of the usual causes and do not provide any new cause to the current state of affairs.
I know, I read it. :P
I liked the thumbnail image yeah. :)
+1
Another very interesting story from @lemouth. Does this mean that the current observation of rise in sea level due to global climate change is due to dark matter annihilation ? I hope Trump is not seeing this.
Of course not. This has nothing to do with climate change (this was the clickbait part of the post :D ).
The point is that dark matter can contribute to the heat flow originating from Earth. We have measured this heat flow. Thus we can constrain the properties of dark matter.
Okay. I got it. Dark matter was always being annihilated inside the earth through out it's history. Hence we can't attribute the recent observation of the rise in temperature to the dark matter annihilation. But what if suddenly earth is being hit by more dark matter than usual ?
No we can't. There are models, for which dark matter can be captured by Earth and annihilate inside it. In this case (and only for those models), there is a heat flux that is generated. This contribute to the total heat outcome of the planet (that we know with some precision) and we must only make sure that there is no inconsistency with the observations.
Does it clarify?
We can estimate the local density of dark matter. There is no way this can suddenly change without messing up the entire cosmology.
Haha the picture is complete funny!
Let's get to the science: In theory, how big is the increase in earth temperature caused by dark matter?
Thanks
Chapper
The picture is indeed great! @pab.ink rocks! :)
Thanks for the good question. It however works in the opposite way. We know the heat flow originating from the planet (this is measured). If there is a dark matter contribution (because the possibility of such a contribution depends on the details of the dark matter model), then it is part of what we measured. When a theory is built, physicists must then pay attention not to generate too much heat flow from the planet.
Therefore, as said in another comment, this does not affect in any special way the observed temperature variations.
I appreciate the time and creativity you put into this post, but dark matter is after decades still unproven and probably a complete fairy tale. A very simple explanation for cosmological observations comes from the electric universe theory. Maybe you will give it a try:
Unfortunately, I have to disagree. There is no scientific backup to what you said and you cannot say that a theory is wrong until it has been proven wrong... This is how science works I am afraid.
First of all, we have data. Standard cosmology, thus with dark matter, is the simplest explanation that agrees the best with data. Of course, this is not perfect and this is not the only explanation. But what standard cosmology solves is already amazing. In addition, there is nothing in data that excludes dark matter and standard cosmology. For this reason, no one is allowed to say "it's a fairy tale". At least not yet.
In contrast, the electric universe has serious flaws that have never been addressed (google it, you will find hundreds of hits). In addition, I have never found any rigourous formulation of it. From there, there is only one possible conclusion I am afraid...
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Very informative post. Lots of thing i learned from you today.
Glad that you liked it! :)
How dare you?
😂
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Because it is funny (and an interesting idea)?
i was mocking the lady on your Thumbnail ;)
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I know I know don't worry. That's the price to pay when one becomes a public figure ;)
Thanks for the post.
You are welcome :)
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