Hubble Finds 10 Times More Galaxies Than Thought
nasa.gov
nasa.gov
https://en.wikipedia.org/wiki/Dark_matter#Observational_evid...
The average mass density of the universe is known within a few percent.
http://hyperphysics.phy-astr.gsu.edu/hbase/astro/denpar.html
From reading the article, I believe this is literally just a finding about how many galaxies into which the known amount of matter was clumped in the distant past, i.e., more galaxies with less average mass.
"found that 10 times as many galaxies were packed into a given volume of space in the early universe than found today. Most of these galaxies were relatively small and faint, with masses similar to those of the satellite galaxies surrounding the Milky Way. As they merged to form larger galaxies the population density of galaxies in space dwindled. This means that galaxies are not evenly distributed throughout the universe's history,"
I read this as they did not find new visible matter, but they discovered that the visible matter was distributed in many more small galaxies compared with today. I could be wrong though, I'm by no means an expert in this field.
We've known for a while now that there seems to be more galaxies out there, heck before the hubble went up we didn't even knew how much there is. There are also indications that there is considerably more intergalactic material out there than we've suspected before.
However the problem is that "dark matter" is also needed on local scales, including our solar system; this is a good read http://scienceblogs.com/startswithabang/2013/01/18/why-the-u.... So "dark matter" is needed to explain our current model of gravity both local and global scales; it is important to note tho that "dark matter" is a placeholder it doesn't necessarily have to be a new type of matter (e.g. AXIONs), some irregular mode for normal matter (e.g. WIMPs) or or it can be regular matter which isn't easily observable (e.g. MACHOs) or it can be also be any combination of the above, and things we haven't even considered yet.
Alternatively we might need to rethink our understanding of gravity, and of the existing forces in general, a good point to note is that gravity isn't a traditional force in the first place which already sets it apart from the bunch (it's a property of the distortion of spacetime, it also is only attractive unless dark energy is somehow a very low/zero value property of the gravitational field).
So gravity might not work like we think it does, it might be hiding another elementary force, or it might be that gravity on certain scales/conditions splits into multiple forces similarly to how the electroweak force works (at some point during/prior to the big bang all forces/fields were unified at least in theory).
Mainstream Physics have been stuck somewhat for a fairly long time on certain aspects, there is also quite a bit of misconception about what works and what doesn't for example most people think that quantum gravity doesn't work which it does, you can use it for everyday life and for many other things, you can't use it during the big bang (and shortly after) and it breaks down near very strong fields e.g. a singularity which is also the internal killswitch or "mathematical contradiction" embedded within general relativity where gravity and spacetime as we know it break down.
Caveat++: That light reaching earth from far away galaxies was then, this is now.
I'm sure the number of solid bodies — potential habitats for life or artificial constructs — in our universe is magnitudes larger than the number of stars we've detected, and the latter is already a mind boggling quantity.
The best method is to notice when a planet passes in front of its star, by how it gets slightly dimmer. That only works if its orbit happens to be directly between us and that star.
Given how little we actually spend on this sort of stuff, I'd be happy if we could save Hubble, rather than let it retired and reenter the atmosphere and burn. Perhaps a robotic mission to repair it in 2025 can be added to our big plans to go to Mars, etc.
https://upload.wikimedia.org/wikipedia/commons/4/42/JWST-HST...
[1]: http://www.skyatnightmagazine.com/news/galaxy-found-9999-dar...
I heard that the nighttime sky is dark simply because the universe is to young for the whole thing to get filled with light, though that will happen eventually.
Crap, I can't remember where I read that. Somewhere linked off of HN. Nautil.us?
Also, a lot of astronomy goes on the assumption that the laws of physics are the same far away as they are near by, and that they don't change over time. It's possible that if either of these two assumptions are incorrect that anything goes.
I'm also reminded of Arthur C. Clarke's famous dictum that, "when a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong."
What does a big crunch have to do with it? Maybe I don't know what a big crunch is... I currently think the big crunch is the idea that gravity will eventually coalesce all matter into a single point.
In an expanding universe, objects can be separated by a cosmic horizon. Nevertheless, from the comoving perspective, they may very well still move towards each other - but without ever meeting up. However, if you extended conformal time beyond infinity, they would. That's of course not physically possible, so that particular comment was tongue in cheek.
Think of it another way—if you're in an oven at 5800K, there is no arrangement of matter you can put inside that will not eventually come to thermal equilibrium.
Is the horizon spherical?
The speed of light. Things beyond the horizon are things where the light hasn't had time to reach us yet.
> Is the horizon spherical?
Given that the speed of light is isotropic, yes.
> The speed of light. Things beyond the horizon are things where the light hasn't had time to reach us yet.
No. Things within the horizon are things where the light hasn't had time to reach us yet.
Things beyond the horizon are things where no amount of time will ever enable the light to reach us. That's what makes it "unobservable".
If we move away from an observer in our accelerating universe we first pass objects that can still emit light that can reach the observer, then we pass the cosmological event horizon and enter a region where objects were once able to emit light reaching the observer but which are now moving away to fast for they light emitted now to ever reach the observer and finally we pass the particle horizon and enter the unobservable universe where objects were never able to emit light able to reach us.
This may sound contradictory but one mus keep in mind that objects between the cosmological event horizon and the particle horizon emitted light in the past that is still on its way to us so that we can still observe those objects for some time but they can just no longer emit light that will reach us.
Also note that I avoided talking about the inside and outside of horizons because I am not sure what side is usually called the inside respectively the outside. From the point of view of an observer he is inside the horizon, on the other hand in analogy with a black hole where the horizon prevents light reaching an observer outside the horizon we would have to call the observer outside of the horizon. I think the former point of view is the common one but I am absolutely not sure about that.
EDIT: Replaced Hubble horizon with cosmological event horizon as pointed out by cygx.
Both can be defined in terms of certain velocities reaching c: The hubble sphere is located where the change in proper distance at constant cosmological time reaches the speed of light (aka recession velocities), the cosmological event horizon is located where relative velocities as evaluated by parallel transport along the light path does so.
Due to conformal flatness of the FLRW metric, it's possible to represent the Hubble flow as vertical lines, the spatial surfaces at constant cosmological time as horizontal lines and light rays as straight lines angled at 45°. The geodesics for massive particles not following the Hubble flow however would be more complicated, but are of no particular interest.
The big bang happens at the lower edge of the paper, the upper edge represents t=inf. The observable universe is bounded by two light rays that meet at infinity. In our toy model with 1 spatial dimension, if an observer follows the Hubble flow along a vertical line, the number of observable galaxies will be proportional to the width of the intersection of the cone formed by light rays and the horizontal line representing space at the time when galaxies first formed.
As ASCII, it looks like this:
conformal time
^
| "us"
t=inf +------------x------------+
| /|\ |
| / | \ <------------ cosmic event horizon
| / | \ | (bounds observable universe)
| / | \ |
t=now +-------/----x----\-------+
| / /|\ \ |
| / / | \ <------------ light emitted by farthest
| / / | \ \ | visible galaxy as it formed
| / / | \ \ |
+--x----x----|----x----x--+ <---- time of galaxy formation
| /: : | : :\ |
|/ : : | : : \|
t=0 +--:----:----+----:----:--+---> comoving distance
: : : :
: |<------->| <--- currently visible galaxies
: :
|<----------------->| <--- asymptotically visible galaxies
As time goes by, we will continue to observe new galaxies being formed, which increases the total number of theoretically visible galaxies. In practice, redshift may again prevent us from doing so in practice.
Because they may create new ideas which impact models, frameworks, directions, and analogies of thought in experimental and theoretical disciplines of the same or differing subjects?
Because not everything is testable, or even when it is the number of variables simply makes controlling the experiment for accurate causal derivations difficult to impossible? (increasingly true as science progresses, often leading to false levels of confidence).
Hmm......
How do you figure? Whether we are in a simulation is a) unknowable by definition, or it's not a very good simulation, and b) doesn't change anything about how our universe works from our perspective. Why would speculation about "why" impact anything about the decisions we make?
If, as most people, you think that one's beliefs shape one's actions, then it should be pretty clear that a belief that we live in a simulation could lead to some people acting differently based on that belief.
Only if one did not have free will or if one's beliefs did not shape one's actions would such a belief have no potential impact.
This is completely nonsensical.
> or might start not taking life seriously.
People already do this just fine.
> Only if one did not have free will or if one's beliefs did not shape one's actions would such a belief have no potential impact.
Free will is a pretty thought, not anything to do with a simulation theory. Why does it matter whether you are forced to bow down to physical laws vs simulated physical laws? You can tell yourself whatever you want, but you gotta bow.
> This is completely nonsensical.
It really depends on the nature of the simulation. For example, if the simulation was something like what was depicted in The Matrix, where one's experience or senses were being simulated while one's real body was outside the simulation, then it could be possible to find a way out.
Of course, if your entire existence was simulated and you had no existence outside the simulation, then it would be more difficult, but perhaps even then not impossible, depending on whether you believed that a copy of yourself was still you. For instance, one could conceivably "upload" a copy of one's mind/brain in to a robot that was external to the simulation and that robot could then potentially have access to sensations/experience outside the simulation. Of course, then it could be argued whether that's another simulation.
But the potential for whatever is "outside" the simulation being just another simulation (ala Inception) is always there. And I'm not sure how one could ever be certain one was ever really "outside" and not just in another simulation -- though it might be possible that one really is "outside" without being certain of it. Or one could be certain and mistaken, or certain and correct. But then one could always be mistaken.
> > or might start not taking life seriously.
> People already do this just fine.
I meant people who took their life seriously because they thought it was "real" and then finding out that they and everyone/everything around them was simulated might decide, as a result of this realization, to no longer take life seriously. For example, they could have valued human life before, but when realizing that the beings they thought were alive before actually weren't, then they could start not valuing them anymore.
Of course, some people don't value their own lives or those of others regardless, and don't take their life seriously anyway.. but I'm not talking about them.
> Free will is a pretty thought, not anything to do with a simulation theory.
The point of bringing up free will was to show under what circumstances one's beliefs would not have any impact on one's actions. Those circumstances are ones in which one does not have free will.
If one does have free will, and one's actions really are shaped by one's beliefs, then the belief that one is in a simulation could have an effect on what one does.
If one does not have free will, or one's actions are not shaped by one's beliefs, then the same belief would not have any effect one what one does. One would do what one was determined to do regardless.
Original scenario of The Matrix had it until some businessman decided to turn it into another happy-end hollywood crap, afaik.
It possibly does: https://en.wikipedia.org/wiki/Simulation_hypothesis#Testing_...
Take a look at Hindu mythology. The idea that the world is an illusion or a dream was quite common as far back as 3 or 4 thousand years ago, and has lasted on through the present.
Another version of that belief was made famous by Plato 2500 years ago. Then Zhuangzi's famous "Now I do not know whether I was then a man dreaming I was a butterfly, or whether I am now a butterfly, dreaming I am a man." came about 2300 years ago. Then yet another version by Berkeley about 250 years ago.
The whole "the universe is a simulation" is just the most recent variation, that came about with the advent of computers.
People in this thread are being way too dismissive of an idea that couldn't possibly have been expressed or understood without modern computational science, specifically the notion of Turing equivalence.
The Sufis symbolized the worldly existence and our apparent multiplicity as 'foam on the surface of an ocean' (c.f. Quantum cosmology and quantum foam), with the true reality being the eternal sea.
In both, "the Real" is the true Self, the "infinitesimal" that is "the Most High"; and the "outward world" the microcosom and the true macrocosom the inner reality of Man.
Buddhism (how could I have neglected to mention it?) also has the illusory nature of the world (and of the self) as a central tenet -- though what that actually means varies with the strand of Buddhism you're talking about.
The world as illusion was even a belief of some Gnostics, who lived a couple of thousand years ago.
Regarding Buddhism, in the Lotus Sutra, the Buddha, to the apparent dismay of a few thousand attendees -- they get up and leave! -- informs that the Three Vehicles are merely devices to reach various levels of understanding, and that this world ("a burning old house") was an attraction that attracted his children but unfortunately they got caught up in the illusion and now need enticements (the Three Vehicles) to rescue them from the burning old house.