Layman's Guide To Understanding Modern Cosmology (dark energy, dark matter, higgs field etc)

Most of us have heard of "dark matter" and "dark energy", but do you really know what these terms mean? Modern Cosmology can be extremely difficult to grasp with all these different mechanisms which seem to be little understood. The truth is scientists still don't know much about dark energy or dark matter, hence their names.

It's taken me quite some time to get a real handle on these concepts, now my aim is to explain these ideas in the simplest way possible, as I seem to have a knack for that. These ideas really aren't that difficult to grasp, it's just that they have many different names and there are many theories concerning what dark energy and dark matter are.

Dark Matter

We will start with dark matter, because amazingly enough, this is probably the easiest to explain and understand out of all the following concepts. Dark matter is similar to normal matter as far as we know, except that we can't detect it. The reason we know it must be there is because it has a gravitational effect just like normal matter. Since huge objects bend space, photons (light) travelling near those large objects will follow a curved path around the object.

This essentially causes large objects (such as galaxies or clusters of galaxies) to act as huge lenses. Objects behind the galaxies can be magnified and distorted by the gravitational lensing effect. So we can use this to measure the mass of far off galaxies simply by looking at the degree to which they bend the space around them. Our calculations show us that there is much more mass in those galaxies than we are able to directly observe with out telescopes.

In fact we can't even detect this so called dark matter. After all it must exist in our own galaxy, but to date we haven't been able to detect it with our instruments. It's basically invisible mass which seems to be completely undetectable other than the gravitational effects it has on space. It is estimated that dark matter makes up about 85% of all matter. The total energy-density of the universe is estimated to consist of 70% dark energy, 25% dark matter, 5% normal matter.



We will move onto dark energy next, but it's important to note that dark energy and dark matter have no real connection other than their names. Dark matter might be called dark matter because we can't detect it, but it's also probably partly because we don't fully understand the real nature of it. We also don't full understand dark energy so they are similar in that respect, but as we'll see they are two very different concepts (they may have some deeper connection however).

Dark Energy

Dark energy is the energy responsible for the expansion of the universe. There are many theories about what it could be, it may be some type of energy fluid or field or it may be an inherent energy of empty space (vacuum energy caused by virtual particles). A more familiar name for dark energy is Einstein's "cosmological constant". The cosmological constant is a mathematical constant which describes how much energy empty space must have to account for inflation.

The simplest explanation for dark energy is that it is simply the "cost of having space": that is, a volume of space has some intrinsic, fundamental energy. This is the cosmological constant, sometimes called Lambda (hence Lambda-CDM model) after the Greek letter Λ, the symbol used to mathematically represent this quantity. Since energy and mass are related by E = mc2, Einstein's theory of general relativity predicts that this energy will have a gravitational effect. It is sometimes called a vacuum energy because it is the energy density of empty vacuum. In fact, most theories of particle physics predict vacuum fluctuations that would give the vacuum this sort of energy. This is related to the Casimir Effect, in which there is a small suction into regions where virtual particles are geometrically inhibited from forming (e.g. between plates with tiny separation).

Dark Energy

Inflation, if you are unaware, is a term describing the expansion of space. Yes, the space between galaxies is expanding, which moves us further away from all galaxies around us. It's not actually that all other galaxies are zooming away from us due to motion (some may be), but the main reason they appear to move away is because the space between our galaxies gets stretched out. Gravity counter acts the expansion of space so that's why the space inside our galaxies doesn't expand in the same way.

So when space expands (due to the vacuum energy), it causes inflation. However the new space which is created in that expansion process also contains this vacuum energy. The energy is an inherent property of space so when the space expands the energy doesn't become diluted. The new space brings with it new vacuum energy. Thus the rate of expansion doesn't slow down, creating the illusion of an accelerated expansion; the further away from us the object is the faster it seems to be moving away from us.

Remember that it's the space expanding, so when the galaxy is further away from us there is more space between us undergoing expansion. Once there is enough space between us it will be moving away from us faster than the speed of light (this is consistent with the general theory of relativity), and the light from that galaxy will no longer be able to reach us. This represents the end of the "observable universe", it is like the event horizon of our universe (from our frame of reference).

So at some distant point in the future we wont be able to see anything outside of our own galaxy because everything will be beyond the event horizon. There are many reasons we know the space in the universe is expanding, most prominently the work done by Hubble in measuring the brightness of special distant supernovae and the work following on from his. In order to explain this expansion we need some sort of mysterious energy, and that's where dark energy/vacuum energy comes into play.

You also have to remember that if the Universe is "flat" and infinite (flat in a 3D sense) it means nothing is really "getting bigger" unless you consider one infinity larger than another infinity (debatable). But if the universe is not infinite (meaning the universe curves back in on its self) then we can say it is expanding at an exponential rate, since the larger it gets, the more space it will contain, and the new space is also expanding. But from our perspective the end result is the same.



However we do have ways of measuring the shape or geometry of the universe. We can look at the afterglow of the big bang (cosmic microwave background radiation) and with some clever tricks which I don't have time to get into we can measure the shape of the universe. Recent measurements by the WMAP spacecraft indicate that the universe is probably "flat", or so close to flat we can't measure the curvature. And we know that for the universe to be this flat it must have a certain critical density.

We have ways of measuring the total amount of matter in the universe, but when we measure the total amount of matter in the universe (including dark matter) we find that there's only about 30% of the critical density required. This indicates the existence of another type of "dark" energy which can account for the remaining 70% and also help us explain inflation. However we find that 70% dark energy would cause a far greater acceleration of the universe than what we measure.

To reconcile this we require yet another mysterious force/energy which acts to provide a positive pressure to cancel out the negative pressure of the dark energy (the negative pressure causes the expansion). But this mysterious new energy must not entirely cancel out the dark energy, it must leave the amount we were looking for to account for the correct rate of expansion which we measure. You may begin to see why this is hard to learn.

The cosmological constant is estimated by cosmologists to be on the order of 10^-29g/cm3, or about 10^-120 in reduced Planck units. Particle physics predicts a natural value of 1 in reduced Planck units, leading to a large discrepancy.

A major outstanding problem is that most quantum field theories predict a huge cosmological constant from the energy of the quantum vacuum, more than 100 orders of magnitude too large.[3] This would need to be cancelled almost, but not exactly, by an equally large term of the opposite sign.

Dark Energy

Higgs Field

There are several reasons we know the universe must have expanded very rapidly near the beginning of the big bang, but one of the main reasons is because the matter in the universe is spread out so evenly/uniformly/homogeneously. The matter is also spread out isotropically, meaning it's the same type of matter everywhere we look (on large scales). This unusually even distribution can be explained by a rapid inflationary period.

Remember the big bang supposedly started as some type of extremely dense and small sphere of energy. As the space rapidly expanded during this period it caused the energy to be distributed over a huge volume of space in an extremely small length of time, creating the rather even distribution we observe today. But why did this period of rapid inflation occur for just a short time and then stop? This is where the Higgs field comes into play.

According to our standard model of particle physics there should be (it's not really proven yet) a field called the Higgs Field which gives particles their mass. The infamous Higgs Boson is basically a type of particle which is predicted to exist as a result of this field. During the early phases of the big bang the Higgs Field was essentially still turned off due to the extreme conditions, and all particles were massless. Without the Higgs Field everything can move at the speed fo light.

This would seem to imply that gravity did not yet play a role at this early point in time, and if you recall, gravity acts to work against the dark energy and the inflation of space it causes. I will also go out on a limb and say that the Higgs Field may be the mysterious force we were seeking earlier, to cancel out the dark energy's negative pressure. Without the Higgs Field active the negative pressure from the dark energy is dramatically stronger.

Please note that the last paragraph is fairly speculative, I mean I'm not exactly certain about how the mechanics of these early phases of the big bang operated. Not to mention this exact topic is still a huge mystery to scientists. We don't really know what dark energy is and how it is canceled out or what may be working to cancel it out. However everything else I've written up until the last paragraph should be very solid stuff (look it up).

The Big Picture

Myself and many others are having a bit of trouble seeing the big picture here, but there are many conclusions to draw from what we know so far. We have seen that dark matter and dark energy are very different things. Dark matter exerts a gravitational force like ordinary matter, and gravity works to slow the expansion of the universe. On the other hand, dark energy causes space to expand exponentially. There's also one other nice feature of this framework.

If we did live in a curved universe the math tells us we must have energy at the beginning of time. The benefit of having a flat universe and an energy-density which corresponds to the critical density of such a flat universe, is that the energy of the universe can come from nothing because the total amount of positive energy and the total amount of negative energy cancel each other out. Gravity has negative energy which cancels out the positive energy of matter.

Now lets not get caught up in the technical specifics of what positive and negative mean in relation to dark matter and dark energy, the point is the total average amount of energy in the universe adds up to zero if you take the negative energy from the positive energy. So the basic theory is that quantum fluctuations can create the energy of the universe from nothing (by spontaneously creating an equal amount of positive and negative energy), and probably have done so an infinite number of times before.

Now one must keep in mind how truly and radically different this concept of a flat universe is compared to the pervasive but wrong model of a curved universe where the universe is like a self contained or "closed" capsule of space-time. An infinite flat universe is "open", there is no end to space-time. Now you may wonder how can space expand if the universe is infinite? Honestly I can't explain it but the math says it can so I tend to trust the math.

When it comes to infinity I think all our basic intuitive understandings start to break down. That may indeed be why we find it so difficult to understand these weird concepts and why we have such trouble tying them all together into one comprehensive theory. Perhaps it all relates to infinity on a much deeper level than we currently understand and so we are failing to look at the problem from the correct perspective and it looks like nonsense to us.

Further Video Lectures

thank you for taking the time to sum it all up, I already had a pretty good understanding but its nice to see it summarized in laymen terms.

It certainly is a weird and wonderful universe we live and and I believe we still only understand a miniscule amount of whats really going on.

Originally posted by mouldy crumpet
thank you for taking the time to sum it all up, I already had a pretty good understanding but its nice to see it summarized in laymen terms.

It certainly is a weird and wonderful universe we live and and I believe we still only understand a miniscule amount of whats really going on.

Yep we truly don't understand as much as we like to think we understand. Hopefully in my life time I can see some major breakthroughs in this field. I find the origins of the universe to be one of the most fascinating subjects there is. Just understanding how it all got here and why it works the way it does is exciting for me. And I find that writing out threads like this really helps to refine and refresh my knowledge, while hopefully educating others at the same time.

You should include that for dark matter, most of the evidence is actually due to galaxy rotation curves not making any sense.

When you look at a star you can infer its mass from its spectral type and brightness. These relationships are constantly honed and astronomy over the years has improved its understanding. Galaxies while it is often impossible to separate each individual star, for some closer ones it is. Now the amount of light we see from a galaxy is a measure of the amount of mass contained, and the speed at which the gas and stars are moving around the galactic centre are also a measure of the mass contained within the system.

Astronomers expect (based on observation of our own galaxy for example) that the rotation speed of stars from the center out, should first increase, reach a maximum and then reduce with a 1/sqrt(r) relationship. Something like 99.9% of galaxies we observe do NOT follow this relationship and infact have flat rotation curves out to very large radii, this can be explained if the galaxy is sitting within a halo of particles that have significant mass, and are only bound to the system gravitationally.

Lensing effects compound this also, allowing for an alternative measurement of the amount of mass contained within super clusters of galaxies. When scientists unfold the lens to show how much mass is present to produce the observed effect, they see that each lens contains more mass than normal matter/stars in the galaxy can provide, and are also very widely dispersed, meaning alot of mass it contained out to regions that do not have many stars in them, only gas at the very edges of the galaxies.

My best guess is space-time is physical/material in some unknown way, but the distorting of space-time by mass creates waves, and wakes in space time, and these gravity waves are what 'dark matter' is.

I think dark energy is the opposite result, a black hole at the center of a galaxy and stars spiraling around is like the sun at the center of the solar system and planets spiraling around. If gravity is a whirlpool/vortex in space time that massive bodies cause and less massive bodies can fall into this swirl (like debris swirling around an infinite toilet bowl) then perhaps the stars in the outer regions of spiral galaxies arent slung off into space, because as the galaxy is turning its mass is displacing space all around it, as a bowling ball spinning 1,000 mph dropped into a pool would probably displace water in all directions, not to mention the galaxy as a whole is traveling lineraly through intergalactic space-time, so by the time the outer stars are swung around they never are flung off into intergalactic space because they are riding the "banks" of a gravity wave/well/whirlpool caused by the black hole and all other mass in the galaxy displacing space-time in that local area... I think dark energy is; as this is going on, and the galaxy moves, that wave it creates surrounding it, or as the spiral arms spin around, they are pushing/waving space-time in all directions at all times outward from the galaxy... all spiral galaxies in the universe are doing this, so they are all being pushed away from each other...

Another possible way to look at it, is imagine a really elastic blanket that is 100ft. by 100ft. and you have 20 of your friends all stand in even places away from one another,, and you were to draw a manifold/grid over this whole blanket, and where each one of your friends were standing they drew a blank hole. at the same time each of your friends grabs the black hole, (I guess they would have to be mission impossibly hoisted above the blanket for this thought experiment to work, and 4 corners of the blanket would have to sturdely be staked into the ground) and they start twisting the blanket at the points of the black hole... the manifold/grid that was drawn over the whole blanket would start, and not finish stretching, so metrically according to the starting units of distance, distance would be greater between the galaxies, even though they have not moved... Now I dont necessarily know if this is accurate in anyway,, but its what i think of when I hear about 'spatial expansion' and 'gravity wells from space-time curvature and distortion'.

reply to post by ChaoticOrder

it looks like nonsense to us

Sorry for neglecting this thread, but I subscribed to it as soon as you posted it. You've presented some pretty deep theories, and I'll comment soon.

I just wanted to let you know I'm lurking, and will provide my comments in a bit. Patience.

reply to post by ChaoticOrder

This indicates the existence of another type of "dark" energy which can account for the remaining 70% and also help us explain inflation. However we find that 70% dark energy would cause a far greater acceleration of the universe than what we measure.

I just want to make a small correction to what I said above. I explained how we measure the geometry of the universe by looking at the CMB radiation, and we find that it is probably flat. To account for this flatness I mentioned that we need this extra 70% dark energy. The extra 70% is the amount we need for the flat universe we find ourselves in... however when we actually calculate how much vacuum energy there should be in empty space according to quantum theory, we find that it is far too much and would cause a ridiculously fast expansion of the universe. So we assume there must be another force which counteracts and cancels out the vacuum energy, yet leaves us with the 70% we require for a flat universe.

Originally posted by Druid42
reply to post by ChaoticOrder

 

it looks like nonsense to us

Sorry for neglecting this thread, but I subscribed to it as soon as you posted it. You've presented some pretty deep theories, and I'll comment soon.

I just wanted to let you know I'm lurking, and will provide my comments in a bit. Patience.

lol no worries, you have no obligation to post in my threads. It is an intriguing subject though so I'm interested to hear your thoughts on it.

reply to post by ChaoticOrder


From what I can gather...the only way to be able to solve such issues as well as solve the UFT or Unified Field Theory and of course this also means understanding Quantum Mechanics...is to start looking at a Much Larger System.

I am fairly certain that such things are specific to Quantum Particle/Wave Form transfer and exchange within a Multiversal System. Specifically...One Universal Group of a Multiversal System.

Split Infinity...p.s...this is consistent with Quantum Mechanics.

reply to post by SplitInfinity

I am fairly certain that such things are specific to Quantum Particle/Wave Form transfer and exchange within a Multiversal System. Specifically...One Universal Group of a Multiversal System.

Yes I think we need to look outside the box here. I'm personally leaning towards the hypothesis that dark matter is some type of matter within another dimension which exerts a gravitational force across our dimensions. Something like the negative and positive dimensions I described in my other thread titled "Before The Big Bang". When I get some time I want to work on building the exact specifications of this theory and how it all fits together.

Here's another extremely good lecture concerning the origins of the universe etc:

Very interesting. It gives me a better grasp on what they are talking about. It gives me more questions though.

If this is correct does it mean that the universe is really expanding as much as they think. If matter is injecting energy into the dark energy through many different means, the dark energy levels could be increasing. This could mean that the perception we have about it could be distorted and the extra energy in the dark energy sector could just be making it appear that it is expanding because of the change in density of the dark energy. It is like a pane of glass in the sun. It expands but the energy of the glass absorbs the energy because the atoms are energized and the glass expands but also the area between the atoms gets crunched to the same degree, increasing the density of the space between the atoms. I don't know if this would apply to the universe though, this may be something way different. I can picture energy flowing. The bond strength would get stronger and longer with expansion. This action would also alter time. I'm probably off on the wrong track but that's how learning works.

reply to post by ChaoticOrder


Make sure you don't confuse another Dimension with a Alternate Divergent Universal State as the later is more likely the place things such as Dark Matter and Dark Energy are bleeding into this Universe from.

Split Infinity

reply to post by SplitInfinity

Make sure you don't confuse another Dimension with a Alternate Divergent Universal State as the later is more likely the place things such as Dark Matter and Dark Energy are bleeding into this Universe from.

What I'm describing isn't exactly an alternative dimension in the typical way the word is used, it's slightly different. But it's not a "Alternate Divergent Universal State", which I assume is used under the context of some sort of quantum branching theory. I don't believe such divergent universes, assuming they exist, would have any method of interacting with our own universe... especially when you consider there would be a near infinite number of them.

reply to post by rickymouse

If matter is injecting energy into the dark energy through many different means, the dark energy levels could be increasing.

I'm not sure what you're saying, matter doesn't inject energy into the dark energy. Dark energy is a separate energy used to fill the gap in our observations, similar to dark matter. And we do know that dark energy levels are increasing... it must be in order to product an accelerating expansion. Otherwise the dark energy would become diluted as space expanded and the expansion would slow down.

reply to post by ChaoticOrder


Since Matter...and thus the Higgs-Boson...needs at least a Minimum 10 or 11 Dimensional State just to exist...and there are probably more...are you stating that a Higher Demensional State beyond 11 exists were this Dark Matter and Dark Energy is existing.

Personally...I would go with an overlapping Universal Reality NOT specific to our Universal Group within the Multiverse...OR...such things are existing to the Quantum Interconnectivity between Divergent Universal States.

Split Infinity

reply to post by SplitInfinity

Since Matter...and thus the Higgs-Boson...needs at least a Minimum 10 or 11 Dimensional State just to exist...and there are probably more...are you stating that a Higher Demensional State beyond 11 exists were this Dark Matter and Dark Energy is existing.

As far as I know String Theory is the only theory which requires 10 or 11 dimensions to explain particle physics. I'm stating there are only two dimensions, a positive dimension and a negative dimension. Dark matter exists in the other dimension and remains invisible to use but exerts a gravitational force across the dimensions, which is possible for most multi-dimension theories.

reply to post by ChaoticOrder


OK...but pardon me...how are you coming up with Dark and Light Dimensions and since a Dimension is just a term of Geometry that describes the construct of Space/Time and the dimensional nature of all within it...how are you possibly using two specific but seperate on dimensional states to describe Dark Matter and Energy?

Split Infinity