Astronomy

Could matter be infinite?

Could matter be infinite?

Perpetual motion and Big Bang theory seem to allude that the universe can't last forever because matter and energy are dispensed.

Is it plausible the Universe has infinite matter?


Yes. Currently it is at least plausible that the universe is spatially flat. If that is the case then, barring global topological weirdness, it is also spatially infinite. That would mean it contains an infinite amount of matter.

Disclaimer. I don't know how large the uncertainties on spatial flatness currently are: if Wikipedia is to be trusted $Omega = 1.00 pm 0.02$ ($1$ being flat) based on data from WMAP and Planck.


Ask Ethan: Could Gravitons Solve The Mystery Of Dark Matter?

Quantum gravity tries to combine Einstein’s general theory of relativity with quantum mechanics. . [+] Quantum corrections to classical gravity are visualized as loop diagrams, as the one shown here in white. If gravitons are massive, and can be successfully created with the right properties, perhaps they could make up the missing dark matter in the Universe.

SLAC National Accelerator Laboratory

One of the most puzzling observations about the Universe is that there isn’t enough matter — at least, matter that we know of — to explain how we see things are gravitating. On Solar System scales, General Relativity and the masses we observe do the job just fine. But on larger scales, the internal motions of individual galaxies indicate the presence of more mass than we observe. Galaxies in clusters move around too quickly, while X-rays reveal an insufficient amount of normal matter. Even on cosmic scales, extra mass has to be present to explain gravitational lensing, the cosmic web, and the imperfections in the Big Bang’s leftover glow. While we typically invoke a new particle of some type, one intriguing idea is purely gravitational: could dark matter be made of gravitons alone? That’s what Neil Graham wants to know, as he writes in to ask:

“Why couldn’t dark matter be gravitons? Gravitons are undefined as is dark matter. We know dark matter has gravity. Why couldn’t it made of the mythical graviton particles?”

Why couldn’t dark matter be gravitons? Or, better yet, could gravitons make up some or all of the dark matter? Let’s look at what we know, and see what possibilities remain.

This snippet from a structure-formation simulation, with the expansion of the Universe scaled out, . [+] represents billions of years of gravitational growth in a dark matter-rich Universe. Note that filaments and rich clusters, which form at the intersection of filaments, arise primarily due to dark matter normal matter plays only a minor role.

Ralf Kähler and Tom Abel (KIPAC)/Oliver Hahn

The first thing we have to consider is, astrophysically, what we already know about the Universe, because the Universe itself is where we get all of the information we know about dark matter. Dark matter has to be:

  • clumpy, which tells us that it needs to have a non-zero rest mass,
  • collisionless, in the sense that it cannot collide (very much, if at all) with either normal matter or photons,
  • minimally self-interacting, which is to say there are rather tight restrictions on how significantly dark matter can collide and interact with other dark matter particles,
  • and cold, meaning that — even at early times in the Universe — this material needs to be moving slowly compared to the speed of light.

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Furthermore, when we look at the Standard Model of elementary particles, we find, quite definitively, that there are no particles that already exist that would make good dark matter candidate.

The particles and antiparticles of the Standard Model are predicted to exist as a consequence of the . [+] laws of physics. Although we depict quarks, antiquarks and gluons as having colors or anticolors, this is only an analogy. The actual science is even more fascinating. None of the particles or antiparticles are allowed to be the dark matter our Universe needs.

E. SIEGEL / BEYOND THE GALAXY

Any particle with an electric charge is eliminated, as are the unstable ones that would decay. Neutrinos are too light they were born hot and would represent a very different type of dark matter than we have, plus, based on our cosmic measurements, they can only make up about

1% of the dark matter, at most. Composite particles, like the neutron, would clump and cluster together, shedding momentum and angular momentum too significantly they’re too “self-interacting.” And the other neutral particles, like gluons, would also couple too strongly to the other normal stuff out there they’re too “collisional.”

Whatever it is that dark matter is made of, it isn’t any of the particles that we know of. Without those constraints — since the null hypothesis is pretty definitively ruled out — we’re free to speculate about what dark matter might be. And while it’s certainly not the most popular option, there are plenty of reasons why one might want to consider the graviton.

When a gravitational microlensing event occurs, the background light from a star gets distorted and . [+] magnified as an intervening mass travels across or near the line-of-sight to the star. The effect of the intervening gravity bends the space between the light and our eyes, creating a specific signal that reveals the mass and speed of the object in question.

Jan Skowron / Astronomical Observatory, University of Warsaw

Reason #1: gravity exists, and is very likely quantum in nature. Unlike many of the dark matter candidates that are more commonly talked about, there is far less speculation associated with the graviton than almost any other idea in beyond-the-Standard-Model physics. In fact, if gravity, like the other known forces, turns out to be inherently quantum in nature, then the existence of a graviton is required. This stands in contrast to many other options, including:

  • the lightest supersymmetric particle, which would require supersymmetry to exist despite the mountain of evidence that it does not,
  • the lightest Kaluza-Klein particle, which would require extra dimensions to exist, despite a complete lack of evidence for them,
  • a sterile neutrino, which would require additional physics in the neutrino sector and is highly constrained by cosmological observations,
  • or an axion, which would require the existence of at least one new type of fundamental field,

among many other candidates. The only assumption we need, in order to have gravitons in the Universe, is that gravity is inherently quantum, rather than being described by Einstein’s classical theory of General Relativity on all scales.

All massless particles travel at the speed of light, but the differing energies of photons . [+] translates into different wavelength sizes. With a minuscule upper limit on the masses of both photons and gravitons, their energies would have to be incredibly small in order for them to move at a speed slow enough to distinguish it from the cosmic limit of a truly massless particle.

NASA/Sonoma State University/Aurore Simonnet

Reason #2: gravitons aren’t necessarily massless. In our Universe, you can only clump together and form a bound structure, gravitationally, if you have a non-zero rest mass. In theory, a graviton would be a massless, spin-2 particle that mediates the gravitational force. Observationally, from the arrival of gravitational waves (which themselves, if gravity is quantum, should be made of energetic gravitons), we have very strong constraints on how massive a graviton is allowed to be: if it has a rest mass, it has to be lower than about

But as tiny as that number is, it’s only consistent with the massless solution it doesn’t mandate that the graviton is massless. In fact, if there are quantum couplings to certain other particles, it may turn out that the graviton itself has a rest mass, and if that’s the case, they can clump and cluster together. In large enough numbers, they could even make up part or all of the dark matter in the Universe. Remember: massive, collisionless, minimally self-interacting, and cold are the astrophysical criteria we have on dark matter, so if gravitons are massive — and while we don’t expect them to be, they could be — they could be a novel dark matter candidate.

If we imagine the extreme case of a large, massive planet in close orbit around a collapsed object, . [+] like a white dwarf (or better, a neutron star), we could theoretically calculate the expected interaction rate between the planet and the gravitons coming from the central object. An expected 1 graviton would interact every 10 years for a Jupiter-mass planet orbiting close by a neutron star: not very favorable probabilities.

Mark Garlick, University College London, University of Warwick and University of Sheffield.

Reason #3: gravitons are already extremely collisionless. In physics, any time you have two quanta that occupy the same space at the same time, there’s a chance that they’ll interact. If there is an interaction, the two objects can exchange momentum and/or energy they might fly off again, stick together, annihilate, or spontaneously create new particle-antiparticle pairs if enough energy is present. Regardless of which type of interaction occurs, the cumulative probability of everything that can occur is described by one important physical property: a scattering cross-section.

If your cross-section is 0, you’re considered non-interacting, or completely collisionless. If gravitons obey the physics we expect them to obey, we can actually compute the cross-section: it is non-zero, but detecting even one graviton is exceedingly unlikely. As a 2006 study demonstrated, a Jupiter-mass planet in tight orbit around a neutron star would interact with approximately one graviton per decade, which is collisionless enough to fit the bill to describe dark matter. (Its cross-section with photons is comparably laughable in how minuscule it is.) So, on this front, gravitons have no problem as a dark matter candidate.

When a gravitational wave passes through a location in space, it causes an expansion and a . [+] compression at alternate times in alternate directions, causing laser arm-lengths to change in mutually perpendicular orientations. Exploiting this physical change is how we developed successful gravitational wave detectors such as LIGO and Virgo. If two gravitational waves interacted with each other, the waves would mostly pass through one another, with only a tiny fraction of the overall wave(s) exhibiting collisional properties.

Reason #4: gravitons have extraordinarily low self-interactions. One of the questions I commonly get asked is whether it’s possible to surf gravitational waves, or whether, if two gravitational waves collided, they’d interact like water waves “splashing” together. The answer to the first one is “no” and the second one is “yes,” but barely: gravitational waves — and hence, gravitons — do interact in this way, but the interaction is so small that it’s completely imperceptible.

The way we quantify gravitational waves is through their strain amplitude, or the amount that a passing gravitational wave will cause space itself to “ripple” when things pass through it. When two gravitational waves interact, the main portion of each wave just gets superimposed atop the other one, while the portion that does anything other than pass through one another is proportional to the strain amplitude of each one multiplied together. Given that strain amplitudes are typically things like

10 -20 or smaller, which itself requires a tremendous effort to detect, going 20+ orders of magnitude more sensitive is virtually unimaginable with the limitations of current technology. Whatever else might be true about gravitons, their self-interactions can be disregarded.

But some of the properties of gravitons pose a challenge for them to be a viable dark matter candidate. In fact, there are two major difficulties that gravitons face, and why they’re rarely considered as compelling options.

When a symmetry is restored (yellow ball at the top), everything is symmetric, and there is no . [+] preferred state. When the symmetry is broken at lower energies (blue ball, bottom), the same freedom, of all directions being the same, is no longer present. In the case of Peccei-Quinn symmetry breaking, this final tilt to the hat-shaped potential rips axions out of the quantum vacuum with practically no kinetic energy a similar process would need to occur to give rise to cold gravitons.

Difficulty #1: it’s very difficult to generate “cold” gravitons. In our Universe, any particles that exist will have a certain amount of kinetic energy, and that energy determines how quickly they move through the Universe. As the Universe expands and these particles travel through space, one of two things will happen:

  • either the particle will lose energy as its wavelength stretches with the expansion of the Universe, which occurs for massless particles,
  • or the particle will lose energy as the distance it can travel in a given amount of time decreases, due to the ever-growing distances between two points, if it’s a massive particle.

At some point, regardless of how it was born, all massive particles will eventually move slowly compared to the speed of light: becoming non-relativistic and cold.

The only way to accomplish this, for a particle with such a low mass (like a massive graviton would have), is to have it be “born cold,” where something occurs to create them with a negligible amount of kinetic energy, despite having a mass that must be lower than 10 -55 grams. The transition that created them, therefore, must be limited by the Heisenberg uncertainty principle: if it their creation time occurs over an interval that’s smaller than about

10 seconds, the associated energy uncertainty will be too large for them, and they’ll be relativistic after all.

Somehow — perhaps with similarities to the theoretical generation of the axion — they need to be created with an extremely small amount of kinetic energy, and that creation needs to occur over a relatively long amount of time in the cosmos (compared to the tiny fraction-of-a-second timespan for most such events). It’s not necessarily a dealbreaker, but it’s a difficult obstacle to overcome, requiring a set of new physics that isn’t easy to justify.

An illustration of heavily curved spacetime for a point mass, which corresponds to the physical . [+] scenario of being located outside the event horizon of a black hole. If gravity is mediated by a massive force-carrying particle, there will be a departure from Newton's and Einstein's laws that are severe at large distances. The fact that we don't observe that gives us tight constraints on such deviations, but cannot rule out massive gravity.

Pixabay user JohnsonMartin

Difficulty #2: despite our theoretical hopes, gravitons (and photons, and gluons) are all probably massless. Until something’s been experimentally or observationally established, it’s particularly difficult to rule out alternatives to the leading idea of how it ought to behave. With gravitons — as with photons and gluons, the only other truly massless particles we know of — we can only place constraints on how massive they’re allowed to be. We have upper limits of varying tightness, but have no way to constrain it all the way to “zero.”

What we can note, however, is that if any of these theoretically massless particles do have a non-zero rest mass, we’d have to reckon with a number of uncomfortable facts.

  • Gravity and electromagnetism, if the graviton or photon are massive, will no longer be infinite-range forces.
  • If the force-carrying particle is massive, then gravitational waves and/or light wouldn’t travel at c, the speed of light in a vacuum, but rather a slower speed that we’ve simply failed to measure thus far.
  • And you get a theory other than General Relativity in the limit that you take the graviton’s mass to zero, a pathology that requires a number of arguably more uncomfortable assumptions to eliminate. (In particular, they do not allow the Universe to be flat, which we observe only open, and that itself contains instabilities which might be dealbreakers.)

While the idea of massive gravity has gotten a lot of interest over the past decade, including from recent progress spurred largely from the research of Claudia de Rham, it remains a highly speculative idea that may not be workable within the framework of what’s already been established about our Universe.

In this image, a massive set of galaxies at the center causes many strong lensing features to . [+] appear. Background galaxies have their light bent, stretched, and otherwise distorted into rings and arcs, where it gets magnified by the lens as well. This gravitational lens system is complex, but informative for learning more about Einstein's relativity in action. It constrains, but cannot eliminate, the possibility of gravitons as dark matter.

KPNO/CTIO/NOIRLab/NSF/AURA/Legacy Imaging Survey

What’s remarkable is that we no longer ask questions like, “why couldn’t dark matter be gravitons?” Instead, we ask, “if we wanted the dark matter to be gravitons, what properties would it need to have?” The answer, like all dark matter candidates, is that it has to be cold, collisionless, with highly restricted self-interactions, and massive. While gravitons certainly fit the bill of being collisionless and barely self-interacting at all, they’re generally assumed to be massless, not massive, and even if they were massive, generating cold versions of gravitons is something we still don’t know how to do.

But that isn’t enough to rule these scenarios out. All we can do is measure the Universe at the level we’re capable of measuring it, and to draw responsible conclusions: conclusions that don’t exceed the reach of our experimental and observational limits. We can constrain the mass of the graviton and uncover the consequences of what would occur if it did have a mass, but until we actually uncover the true nature of dark matter, we have to keep our minds open to all possibilities that haven’t definitively been excluded. Although I wouldn’t bet on it, we cannot yet eliminate the possibility that gravitons that were born cold are themselves responsible for the dark matter, and make up the missing 27% of the Universe we’ve long been searching for. Until we know what dark matter’s true nature is, we need to explore every possibility, no matter how implausible.


The Raisin Bread Example:

Now, I used to think that our Universe is just all this stuff that's out there and the convex hole that encloses it essentially. Then that stuff is just moving away into an empty void, thus, the convex hull gets larger and the universe has expanded. That is not correct. In fact the stuff of our universe isn't moving through space at all. It's moving with space. That's not weird. The famous comparison is with an expanding loaf of raisin bread. The bread is our universe and the raisins are those stuffed inside like galaxies. As the loaf expands, which corresponds to the universe expanding, the raisins or galaxies are getting further away from one another no matter where you look from. If you're at some point on the raisin and measure the distance to all nearby galaxies, you would find those distances are all getting larger as if you're at the center.

But someone else living in some other galaxy (That is some other point on the raisin) measuring all those distances, would also notice them all getting larger. It seemed like everything is expanding away from them as if they're at the center. So everyone gets this

impression, even though there is no center in regards to the surface.

This means that each of the galaxies in our Universe will move away from each other, But the Stars and other things within each of the galaxy will remain intact because of the local gravity. Before getting into the Hypersphere Universe concept, we need to understand the word ɿlat'.


Infinite Of Big Crunch / Big Bang Should Be A Matter Of Where, Not When

No infinite would be a one time entity or event, nor would it pulse as an existence now and then. It would be "timeless," always and forever in being, a matter then of where not when. Also a matter of how to think of a [constancy] of infinite in [static Universe] being, rather than any [inconstant] finite.

The Big Crunch / Big Bang so-called "beginning" is said to have been a Universe the size of a basketball -- or something like that -- exploding everywhere out from that ball into. everywhere, still continuing in an accelerating expansion outwardly from everywhere to everywhere, whatever. Nothingness to. nothingness, whatever. I've argued against this for decades since nothing in or concerning the Universe, especially if an infinite Universe, is ever lost therefore, also, is ever gained.

Since I argue against a one time entity and event, and also argue against a now and then regularly pulsing entity and event, then the infinite mass density of Big Crunch, and alternate face of Big Bang must be some [where] and probably always observed to be there.

It, that binary infinite duo, is too easy, too simple, to be recognized for what it is. The picture of a basketball sized beginning tied to an illustration of bell-shaped expansion, is backward from the reality of an infinite and the finite. Finite is local and relative. Infinite, herein addressing the infinite mass density of the Big Crunch, alternatively the Big Hole (the big holing or welling) of the Big Bang, is non-local and not-relative. The outland horizon.

Turn the picture of Big Crunch / Big Bang inside-out, to an outside-in picture, therefore the infinite of non-local to the finite of local, which is exactly where we are and exactly what we observe of ourselves and a collapsed distant horizon. Relativity collapses going away from local (finite) to non-local (infinite). From the infinity of local, finite, universes (u), such as our own, to the infinitely dense mass of exactly the same infinity closed, collapsed, to the infinite of non-local Big Crunch Universe (U). This way (to every finite-local universe locality (us)) comes the Big Bang. That way to the ever increasingly dense mass horizon goes gravity's infinity from every finite local center of gravity (to the infinity of the infinite of them all at once all in one collapsed horizon).

Where is the center of an infinite / infinitesimal Universe? It is the anywhere and everywhere point (0-point) in and of that infinite. The anywhere and everywhere finite local. The finite relative. Us.

FYI, in the BB model, there is no center to the expanding universe. Microsoft released a report for kids today showing the universe could be 12.6 billion years old, https://www.microsoftnewskids.com/en-us/kids/video/12-6-billion-years-old-that-s-how-old-the-universe-is-according-to-new-research/vi-BB1etg3P?ocid=msedgdhp

That means a distinct beginning and starting point for the expansion of the universe seen in astronomy today. It is based upon reports for H0 = 75.1 km/s/Mpc, published in 2020.

My observation. 75.1 km/s/Mpc = 2.43381 x 10^-18 cm/s/cm. We can see how sensitive the rate of expansion is to the Hubble time or age of the universe. I use these cosmology calculators, change H0 and use defaults for a flat universe.

Using 75.1 km/s/Mpc and calculator 1, the universe age “It is now 12.716 Gyr since the Big Bang” with defaults for flat universe.

Using 69 km/s/Mpc = 2.23612 x 10^-18 cm/s/cm, the universe age “It is now 13.840 Gyr since the Big Bang.”

Tiny changes to H0 in cm/s/cm can make for some large differences in the age of the universe in the BB model. I am confident the cosmology department has worked out the kinks here FYI. This ignored the cosmological constant issue in GR and expanding space. The universe edge in the expansion is only about 46.5 billion light-years distance from Earth today. See Livescience.com published a report using 46.5 billion LY radius in August 2019, https://www.livescience.com/how-big-universe.html

The rate of expansion at 46.5 billion light years distance using 69 km/s/Mpc works out to 9.83 x 10^10 cm/s, much faster than c velocity in Special Relativity From what I can tell, the expansion rate during inflation epoch

3 x 10^30 cm/s/cm or some 10^20 faster than c or more. Enjoy

Catastrophe

Approaching asteroid? Is this THE one?

Atlan0101

FYI, in the BB model, there is no center to the expanding universe. Microsoft released a report for kids today showing the universe could be 12.6 billion years old, https://www.microsoftnewskids.com/en-us/kids/video/12-6-billion-years-old-that-s-how-old-the-universe-is-according-to-new-research/vi-BB1etg3P?ocid=msedgdhp

That means a distinct beginning and starting point for the expansion of the universe seen in astronomy today. It is based upon reports for H0 = 75.1 km/s/Mpc, published in 2020.

My observation. 75.1 km/s/Mpc = 2.43381 x 10^-18 cm/s/cm. We can see how sensitive the rate of expansion is to the Hubble time or age of the universe. I use these cosmology calculators, change H0 and use defaults for a flat universe.

Using 75.1 km/s/Mpc and calculator 1, the universe age “It is now 12.716 Gyr since the Big Bang” with defaults for flat universe.

Using 69 km/s/Mpc = 2.23612 x 10^-18 cm/s/cm, the universe age “It is now 13.840 Gyr since the Big Bang.”

Tiny changes to H0 in cm/s/cm can make for some large differences in the age of the universe in the BB model. I am confident the cosmology department has worked out the kinks here FYI. This ignored the cosmological constant issue in GR and expanding space. The universe edge in the expansion is only about 46.5 billion light-years distance from Earth today. See Livescience.com published a report using 46.5 billion LY radius in August 2019, https://www.livescience.com/how-big-universe.html

The rate of expansion at 46.5 billion light years distance using 69 km/s/Mpc for H0 works out to 9.83 x 10^10 cm/s/cm, much faster than c velocity in Special Relativity From what I can tell, the expansion rate during inflation epoch

3 x 10^30 cm/s/cm or some 10^20 faster than c or more. Enjoy

What went before and what is outside our local universe? Answer! Don't try to go around it, going back to the once upon a time infinitely dense mass basketball exploding into. nothingness (into Nowhereland)! I have an answer (it being an infinite [horizon] constant). I gave my answer (a constancy. No before, no outside, (no questions of time "before" and space "outside") needed).

I'm not trying to be offensive. I'm just always running into the considered pat answers that will not address "nothingness" before and outside, or will address only pulsing which is really no answer at all. Again, I am not trying to be offensive with this response.

Atlan0101

Atlan0101

An interesting article in Quanta Magazine is 'Quantum Mischief Rewrites the Laws of Cause and Effect'. A surprise subheading, to me, is 'Correlation, Not Causation', the subtitle itself, since I am very much dealing here in "correlation" (aka "superposition") on the largest scale, the Universe (U). The non-relative non-local infinite [correlation] of Big Crunch / Big Bang Universe (U) as [correlation] of the infinity of local relative finite universes (u). At the level of "infinite" and "'infinity' of finites" there being no such physic as "cause and effect." The infinity of finite universes, in all their 'infinity', simply merge with and as the 'infinite' mass density of the Big Crunch in outland collapsed horizon. From constant of outland collapsed horizon of the infinite to any and every finite relative local point (0-point) in every finite relative local point universe, the space-time and conditional physics (including "causes and effects") of the Big Bang apply. But, again, at the [hyper] level it is all correlation, not causation.

Quantum Mechanics has shown it is not impossible for one thing to have three or more faces at once for one thing to [be] three or more things, all at once. Correlative existence.

Interesting thread. I found 33x references to infinite or flavor of the word here. I also note this in the history of astronomy. 'Six stages in the history of the astronomical unit', https://ui.adsabs.harvard.edu/abs/2001JAHH. 4. 15H/abstract, June 2001.

A very good table showing efforts to measure the astronomical unit starting with Aristarchus near 280 BC. Table 1 on page 16 of the report (attached, page 2 of the PDF). My view. The history of astronomy determining the distance between the Earth and Sun is more secure and confirmed than discussions about infinite or infinity universe or universes using the science of astronomy.

Atlan0101

Interesting thread. I found 33x references to infinite or flavor of the word here. I also note this in the history of astronomy. 'Six stages in the history of the astronomical unit', https://ui.adsabs.harvard.edu/abs/2001JAHH. 4. 15H/abstract, June 2001.

A very good table showing efforts to measure the astronomical unit starting with Aristarchus near 280 BC. Table 1 on page 16 of the report (attached, page 2 of the PDF). My view. The history of astronomy determining the distance between the Earth and Sun is more secure and confirmed than discussions about infinite or infinity universe or universes using the science of astronomy.

Catastrophe

Approaching asteroid? Is this THE one?

I agree with Rod. I cannot accept that wild unfettered imagination has anything to do with stark reality.

Atlan0101

I agree with Rod. I cannot accept that wild unfettered imagination has anything to do with stark reality.

What is outside and beyond the "observed universe"? You just [emphatically] said (in effect), nothing at all! If it hasn't already been observed, it -- according to you -- doesn't exist and will never exist! You cannot accept that 'infinite' (including 'infinitesimal') exists, much less where and what it might be (as I say, it cannot be local, can never be local, therefore can never be a matter of [local] relativity).

Rod actually sees things my way. That is, he sees them to be for me though not for him. He tells me, in effect, he is learnedly methodical, an educated plugger, and I long worked with such. I very much respect such. They've long held and still do, and will always, "hold the fort," as the saying goes, while such as me sortee (sic). Regardless of his being a plugger, I've learned a lot from long [friendly] associations with his like, Even some that were not quite so "friendly." I can learn, and here and there have learned, from him. In my book, Rod is no mediocrity.

"Great spirits have always encountered violent opposition from mediocre minds. " -- Albert Einstein -- And: "As far as the laws of mathematics refer to reality, they are not certain as far as they are certain, they do not refer to reality." Again Einstein: "It takes three dimensions to describe a point."
"If I had eight hours to cut down a tree, I'd spend seven sharpening my ax." -- Abraham Lincoln.
"He is the best sailor who can steer within fewest points of the wind, and exact a motive power out of the greatest obstacles." "The universe is wider than our views of it" Both -- Henry David Thoreau.
"We must make sure that emerging intelligent systems do not self-destruct." -- Harlan Smith, University of Texas at Austin, 1975.
And, last but not at all least: "From a drop of water a logician could infer the possibility of an Atlantic or a Niagara without having seen or heard of one or the other. "-- Arthur Canon Doyle, Sherlock Holmes: A Study In Scarlett.

Atlan0101

Regarding a [local] universe (u) as I describe it, everywhere the collapsed horizon is potentially observable distant from every point (0-point) within (including the Planck horizon distantly down inside (the same horizon)), it, that horizon, will always be observed locally to be the infinite constant of "Big Beginning." Since it is everywhere at a constant distance up and out, and down and in too (an equivalent [constant] distance), from us, which is to say out and/or in from every local relative point of an infinity of local universes / points, where, and when, would the end place/event be? Steven Hawking amusingly answered that question by telling us when the time came travel in any direction outwardly and away toward that distant collapsed horizon fronting the infinite from the particular local here (wherever here is by [then]), would do the job. Indirectly, sort of, he pronounced every here and now 0-point of universe (u) to be the constant of end point. But, as he indicated in saying go out and away (to go forth (Latin 'exodus' ("Exodus"))), not all are that kind of end place/end event at the same time. With that distant constant of horizon in every direction up and out being the constant of "Big Beginning" with all "fountain of youth" flow of energetic life from it being this way [in] to every point of an infinity of points and universes (u), the distribution of end point event, the dead end point event, will always be a spread of here and there, now and then, running from forever to forever.

We are told the flow of expansionist universe is out to infinite. As Hawking said about the panic of the Universe reaching zero point in some kind of a simulation, there isn't any reason to panic, we are there already (always have been there, will always be there). The flow from the collapsed horizon of the infinite Universe (U) (the Big Beginning fountain of youth), as Hawking hinted concerning, is always to us, always toward us (always toward local 0-point center of the infinite). He was one of the first to tell us of a single particle having six faces alternatively being six separate and distinct particles, while still being the single particle. That description fits the supreme entity of Universe (U), being Big Crunch / Big Bang (non-local, non-relative) 'Big Beginning' Universe, while at once being the [infinity of] local relative -- finite -- universes / 0-points ('correlation, not causation'). You can't observe the infinite / infinitesimal. You can't observe infinity. You can only observe a finite [potentiality] of infinity. You can only perceive the infinite.


Answers and Replies

Assumption: mass creates space, right?

If space were finite, then just by standing at the edge of space will create more space?

Ok so me and a few of my physics (& Maths) friends were arguing this.

I argued that it must be finite in size, since the universe contains a finite amount of matter

What evidence do you have of this?

What evidence do you have of this?

My friend who's a mathematician said that in her geometry subject this question was actually brought up. She said that the universe may be a 3-manifold (3D surface?) and it depends on the curvature (negative or positive) as to whether the universe is finite or not.

I just want to know what the consensus is.

Answers to your assumptions:

1) No, matter does not create space. Matter exists in space.
2) No, matter does not expand space. At the earliest epoch of the Universe, there was no matter, per se, but rather pure radiation. The expansion of space is an intrinsic property, set by the initial conditions (Big Bang). Technically, the expansion of space would still occur even if there was absolutely no matter.
3) As physical matter has spatial extension, then I guess yes, matter "needs" space within which to exist.

Well, there are a number of possibilities that have to be considered. But let's just consider one where the universe wraps back on itself. If the universe wraps back on itself based upon its spatial curvature, then current measurements place the spatial curvature to be within 1% of zero, which makes the radius of curvature at least 10 times the Hubble radius, which is a factor of a few larger than the observable universe.

If the universe is flat but still wraps back on itself, then this induces anisotropies, which we should be able to see in the CMB. But we don't. Thus if it does wrap back on itself, it would have to do that very, very far away (again, a factor of a few times the observable universe).

If I understand the Big Bang theory It all started with a finite amount of energy. If space is finite as well then what is the ratio between space and the other finite "stuff" in it?

Olbers' Paradox takes two assumptions, and shows they cannot both be true:
1. The universe is infinite (in time and space).
2. The universe is static (no expansion).

The discovery of the expansion of the universe demonstrates that the second assumption fails, which means that Olbers' Paradox cannot provide any additional information about the truth or falsity of the first.

With expansion, the universe can still be both spatially and temporally infinite without impinging upon Olbers' paradox.

What edges would a spatially infinite universe have?

Dr. Edward Harrison gave the "definitive" answer/solution to Olber's Paradox, in his 1987 book "Darkness at Night: A Riddle of the Universe".

While it is an open question wether the Universe is infinite in extent (space), it is finite in time. i.e., it had a beginning (The Big Bang). We can only look back a finite distance (our Cosmological Horizon), so the light from any stars existing beyond the radius of the Hubble Sphere has not had a chance to get to us yet. Combined with the fact that stars themselves have a finite life-time, there is simply not enough visible stars in our observable universe to make the night sky bright.

As Chalmoth pointed out above, the expansion of the Universe also has the effect of red-shifting any distant luminous objects. Even though stars did not exist at the time of Recombination (Surface of Last Scattering), even the unbelievably intense, incandescent light from this epoch (approx. 370,000 years after Big Bang) has been red-shifted to such low frequency/long wavelengths that it is no longer in the visible spectrum. hence the Cosmic Microwave Background Radiation.

Finally combined with observation that the expansion of the Universe is now accelerating, eventually all galaxies (with the possible exception of the local galaxies that are gravitationally bound with the Milky Way) will pass beyond our particle horizon, and will forever become unobservable. Note that I do not subscribe to the so-called "Big Rip". So, in theory, billions of years from now, our Milky Way will truly become an "Island Universe", just as it was once thought of, up until the early twentieth century.

Hi Brain Dwarf, I don't agree with your reasoning (in your statement): 'because the universe is all there is. then it must be infinite'. Professor Brian Cox touched on the subject of 'Oblers Paradox' during his astronomy program this week. (BBC Stargazing Live, Pt1). He seems to believe (as I do) that the universe is not infinite.

I thought Deuterium's comment about 'red shifted light' was very interesting though.


Could dark matter be another state of normal matter?

Could normal matter be converted into dark matter in a singularity?

#2 rockethead26

I guess it would help to answer your question if we actually knew what dark matter is.

#3 gvk

How would anyone know, since there are no physical theories that are capable of predicting the properties of matter at a singularity? At the very least, a self-consistent theory of quantum gravity would be required, but it is also likely that the standard model of particle physics needs to be extended to significantly higher energies.

Furthermore, it would be hard to test such theories observationally given that singularities we know are possible all exist inside the event horizon of a black hole. Naked singularities have been hypothesized, but there is no observational evidence for their existence.

Edited by gvk, 16 August 2015 - 06:21 PM.

#4 Rick Woods

#5 Herr Ointment

#6 Rick Woods

Sometimes it's tough to observe naked stuff.

#7 MrFeynman

Could normal matter be converted into dark matter in a singularity?

The thing is you could come up with an almost infinite number of ideas of this type, but unfortunately they all mean very little unless they're testable.

#8 mpc755

'Ether and the Theory of Relativity - Albert Einstein'
http://www.tu-harbur. t/it/Ether.html

"Since according to our present conceptions the elementary particles of matter are also, in their essence, nothing else than condensations of the electromagnetic field"

Particles of matter are condensations of dark matter.

'DOES THE INERTIA OF A BODY DEPEND UPON ITS ENERGY-CONTENT?' A. EINSTEIN
http://www.fourmilab. E_mc2/e_mc2.pdf

"If a body gives off the energy L in the form of radiation, its mass diminishes by L/c2."

The mass of the body does diminish. However, the matter which no longer exists as part of the body has not vanished it still exists, as dark matter. Matter evaporates into dark matter. As matter evaporates into dark matter it expands into neighboring places, which is energy.

When a nuclear bomb explodes matter evaporates into dark matter. The evaporation is energy. Mass is conserved.

Edited by mpc755, 17 August 2015 - 06:45 AM.

#9 MrFeynman

#10 NickWDavis

Wow, this just got painful.

#11 mpc755

Wow, this just got painful.

Or, you could understand matter and dark matter are different states of the same 'material'.

#12 Rick Woods

The mass of the body does diminish. However, the matter which no longer exists as part of the body has not vanished it still exists, as dark matter. Matter evaporates into dark matter. As matter evaporates into dark matter it expands into neighboring places, which is energy.

When a nuclear bomb explodes matter evaporates into dark matter. The evaporation is energy. Mass is conserved.

That seems like sort of a stretch from what Einstein said. You're saying dark matter = energy?

#13 mpc755

That seems like sort of a stretch from what Einstein said. You're saying dark matter = energy?

Nope. You have a tank of liquid nitrogen and heat it rapidly so it explodes. As the liquid changes to gas it expands. The destruction caused by the explosion as the liquid converts to gas is energy.

Particles of matter are condensations of dark matter. Think of matter as being the solid form and dark matter being the gaseous form of the same material. When a nuclear bomb explodes the 'solid' matter expands into the 'gaseous' dark matter. The destruction caused by the expansion is energy.

#14 MrFeynman

Having your own ideas about how the Universe works is in itself harmless, but when you position those unproven ideas as fact - whether intentional or not - you risk confusing or even totally misleading those without enough understanding/knowledge to think critically about those ideas (I'm not in anyway suggesting that's anyone in this thread!) and then it is not so harmless.

Edited by MrFeynman, 17 August 2015 - 11:50 AM.

#15 GJJim

The conversion of (normal) matter to energy has been observed and measured with high accuracy. If dark matter creation was part of the process, would it not show up as a discrepancy in the measurements?

#16 mpc755

Having your own ideas about how the Universe works is in itself harmless, but when you position those unproven ideas as fact - whether intentional or not - you risk confusing or even totally misleading those without enough understanding/knowledge to think critically about those ideas (I'm not in anyway suggesting that's anyone in this thread!) and then it is not so harmless.

What if the so-called "boat and water experts" insisted the water moves with the boat analogous to how the steering wheel moves with the boat? Since they are the so-called 'experts' is it okay that they, for whatever reason, are incapable of understanding the boat is moving through and displacing the water? What's more harmful, correctly explaining what occurs physically in nature or insisting the water is moving with the boat as a clump of stuff just like the steering wheel is because that is what the 'experts' say is occurring?

'Dark matter' is now understood to fill what would otherwise be considered to be empty space.

'Cosmologists at Penn Weigh Cosmic Filaments and Voids'
http://www.upenn.edu. ments-and-voids

"Dark matter . permeate[s] all the way to the center of the voids."

'No Empty Space in the Universe --Dark Matter Discovered to Fill Intergalactic Space'
http://www.dailygala. tic-space-.html

"A long standing mystery on where the missing dark matter is has been solved by the research. There is no empty space in the universe. The intergalactic space is filled with dark matter."

I use the term 'dark mass' to describe the mass which fills 'empty' space. Particles of matter move through and displace the dark mass, including 'particles' as large as galaxies and galaxy clusters.

'The Milky Way's dark matter halo appears to be lopsided'
http://arxiv.org/abs/0903.3802

"the emerging picture of the dark matter halo of the Milky Way is dominantly lopsided in nature."

The Milky Way's halo is not a clump of dark matter traveling along with the Milky Way. The Milky Way's halo is lopsided due to the matter in the Milky Way moving through and displacing the dark mass, analogous to a submarine moving through and displacing the dark mass.

'Offset between dark matter and ordinary matter: evidence from a sample of 38 lensing clusters of galaxies'
http://arxiv.org/abs/1004.1475

"Our data strongly support the idea that the gravitational potential in clusters is mainly due to a non-baryonic fluid, and any exotic field in gravitational theory must resemble that of CDM fields very closely."

The offset is due to the galaxy clusters moving through and displacing the dark mass. The analogy is a submarine moving through the water. You are under water. Two miles away from you are many lights. Moving between you and the lights one mile away is a submarine. The submarine displaces the water. The state of displacement of the water causes the center of the lensing of the light propagating through the water to be offset from the center of the submarine itself. The offset between the center of the lensing of the light propagating through the water displaced by the submarine and the center of the submarine itself is going to remain the same as the submarine moves through the water. The submarine continually displaces different regions of the water. The state of the water connected to and neighboring the submarine remains the same as the submarine moves through the water even though it is not the same water the submarine continually displaces. This is what is occurring as the galaxy clusters move through and displace the dark mass.


This Is How Mastering Dark Matter Could Take Us To The Stars

The hyperdrive from Star Wars appears to depict an ultra-relativistic motion through space, . [+] extremely close to the speed of light. Under the laws of relativity, you neither reach nor exceed the speed of light if you're made of matter. But you might be able to approach it if you had a large-enough amount of an efficient-enough fuel. Dark matter could fit exactly the conditions we need to make this science-fiction dream a reality.

Dark matter is one of the biggest mysteries in all of modern science. Everywhere we look on large cosmic scales — from low-mass galaxies to the largest galaxy clusters, from the cosmic microwave background to the cosmic web that traces the Universe's structure — we can see the imprints and effects of its presence. For every proton's mass worth of normal matter, there's five times as much dark matter, out-massing and out-gravitating the conventional stuff that makes up everything we've ever directly detected.

Even though we have yet to directly detect it, and even though we aren't sure exactly what its true properties are, dark matter holds a tremendous promise for the future of humanity. Ubiquitously located all throughout the galaxy and far beyond, dark matter could be the perfect fuel that makes our interstellar dreams come true. Here's the story of how.

A logarithmic chart of distances, showing the Voyager spacecraft, our Solar System and our nearest . [+] star, for comparison. If we ever hope to travel across the great interstellar distances, it will require a technology that's superior to chemical-based rockets, and hopefully that will include the discovery of a fuel that can be replenished as we traverse our path through the galaxy.

Whenever humanity sets our sights on exploring the depths of space, there are constraints we can't avoid: the laws of physics. In order to accelerate a spacecraft — or any mass — you have to impart an impulse to it in order to change its momentum. The larger the impulse, the more you can change an object's speed. All that determines the magnitude of an impulse is how much force you apply and how long you apply it for.

In a conventional rocket, that impulse is provided by rocket fuel that undergoes a combustion reaction, which produces impulse in the form of thrust. Although this is the best method humanity has come up with for space travel so far, it's incredibly limiting. All of our past and current rockets are chemical-based, unfortunately, and that places tremendous constraints on how far we've been able to go.

This 2015 engine test shows the firing of SpaceX's Raptor engine, which relies on an extremely . [+] powerful and fuel-efficient reaction. Unfortunately, it's still a chemical-based reaction, and converts only about one-millionth of the fuel's mass into energy. We will have to do better if we want to achieve our interstellar dreams on timescales of a human lifetime.

The reason for this is simple: in order to produce thrust — i.e., in order to impart an impulse to your spacecraft — you have to convert that stored chemical energy in the fuel into kinetic energy that pushes your spacecraft. In order to generate that energy, however, you have to use up some of that fuel you're carrying with you.

The key to getting lots of thrust, and therefore lots of acceleration, is fuel efficiency. Certain types of fuel are more energy-efficient than others, meaning that we can get more energy (and thrust, and acceleration) out of, say, 1 kilogram of some types of fuel. An easy way to think about this is through Einstein's most famous equation: E = mc 2 . If you had a perfect, ideal fuel, it would convert 100% of your fuel's mass into energy, enabling you to make the most efficient fuel imaginable.

The launch of Cassini, on October 15, 1997. This spectacular streak shot was taken from Hangar AF on . [+] Cape Canaveral Air Force Station, with a solid rocket booster retrieval ship in the foreground. For all of our history on Earth, the only way we've ever reached space is through the use of chemical-based fuels.

At most, though, chemical-based reactions are somewhere around 0.0001% efficient. The reason is as follows: chemical reactions rely on electron transitions between atoms and molecules. Most of an atom's mass is in the form of protons and neutrons, each of which have a mass that contains around 10 9 eV worth of energy. Electron transitions, however, are on the order of a few (typically 1-10) eV of energy. Even with all the chemical-based tricks we can perform, there are no known reactions that allow us to improve on this.

Sure, we can go for some type of nuclear fuel, but that's only marginally better, achieving efficiencies of around 0.1%. It's a huge improvement, if we can realize it, but there's still a fundamental problem with accelerating to speeds that will carry you interstellar distances on reasonable timescales.

The Tsiolkovsky rocket equation is required to describe how fast a spacecraft that burns through a . [+] portion of its fuel to create thrust can wind up traveling through the Universe. Having to bring your own fuel on board is a severely limiting factor as far as the speed at which we are capable of traveling through intergalactic space.

Skorkmaz at English Wikipedia

The key problem is as follows: whenever you burn fuel, you have to accelerate the entire mass of your spacecraft, including any fuel that's still on board.

Read that again: including any fuel that's still on board.

In other words, let's imagine you can shoot exhaust out of your vehicle at an incredible rate: 100,000 mph (about 160,000 kph), relative to the rocket itself. If you start off with a rocket where 99% of your initial mass is fuel, and you assume that your fuel is perfectly 100% efficient (as though it were pure matter-antimatter annihilation), you'd wind up with a final speed of 460,000 mph (740,000 kph). Even at this record-setting rate, it would still take thousands of years to reach the nearest star.

All rockets ever envisioned require some type of fuel, but if a dark matter engine were created, new . [+] fuel is always to be found simply by traveling through the galaxy. Because dark matter doesn't interact with normal matter (mostly) but passes right through it, you wouldn't have any difficulty collecting it in a specific volume of space it would always be there as you moved through the galaxy.

On the other hand, there's another approach to interstellar travel that could — in principle — make our science-fiction dreams come true. Instead of bringing your fuel with you, what if you collected it as you went? Typically, ideas like this involve enormous magnetic fields that funnel charged particles into some sort of "trap" in your spaceship, allowing you to put nuclei and electrons together where you can then extract energy and perform further reactions with them.

But dark matter offers a tremendous advantage over normal matter in this regard. Why? Because you don't have to do anything special to collect it. It's literally everywhere, distributed in an enormous halo surrounding and encompassing every large galaxy we know of, including the Milky Way. If we find ourselves anywhere in the galaxy, there's bound to be dark matter lying around.

While stars might cluster in the disk and the normal matter might be restricted to a nearby region . [+] around the stars, dark matter extends in a halo more than 10 times the extent of the luminous portion. It is truly found everywhere humanity has dreamed of traveling in our own galaxy, and in many places beyond.

The second tremendous advantage comes from the progression away from chemical-based rockets and towards the idea of a perfect fuel. For chemical-based rockets, 0.0001% energy efficiency is the best we can hope for. For nuclear-based rockets, fission power might get us up to 0.1% efficiency, and nuclear fusion might get us a little further: perhaps up to 0.7%.

The ideal configuration would be to use matter-antimatter annihilation, which is 100% energy efficient. The downside of matter-antimatter annihilation comes with a terrible cost, though: it takes a tremendous amount of work, energy, and effort to create an extraordinarily small amount of antimatter. If you took all the particle physics laboratories ever constructed on Earth and added up all the antimatter humanity has ever created, from Fermilab to CERN, you'd wind up with less than a microgram of antimatter.

A portion of the antimatter factory at CERN, where charged antimatter particles are brought together . [+] and can form either positive ions, neutral atoms, or negative ions, depending on the number of positrons that bind with an antiproton. If we can successfully capture and store antimatter, it would represent a 100% efficient fuel source, but many tons of antimatter, as opposed to the tiny fractions of a gram we've created, would be required for an interstellar journey.

Sure, E = mc 2 might be the most efficient way to extract energy from mass in the entire Universe, as it represents perfect efficiency. But even if you manage to contain and store your antimatter successfully and annihilate it only at the proper moment, you'll still have a finite supply of fuel that required an incredible amount of energy to collect. Once you use up this perfect fuel, you're all out, and all you can do is travel at a constant velocity through space for an indefinite duration of time. Even if we could generate an arbitrary amount, we'd still be fundamentally limited with an antimatter rocket.

That's why the promise of a dark matter fuel source is so alluring. Not only might dark matter be an unlimited fuel source (in terms of abundance) that we don't have to carry on board with us, but it might have that perfect, 100% efficient matter-to-energy conversion potential we so strongly desire.

Our galaxy is thought to be embedded in an enormous, diffuse dark matter halo, indicating that there . [+] must be dark matter flowing through the solar system. Although we have yet to detect dark matter directly, its abundant presence throughout our galaxy and beyond might provide a perfect recipe for the perfect rocket fuel imaginable.

Robert Caldwell & Marc Kamionkowski Nature 458, 587-589 (2009)

There are a multitude of experiments looking for the collisions of dark matter with both normal matter and itself. In general, there are two types of particles in the Universe: fermions (with half-integer spins) and bosons (with integer spins). If dark matter is a bosonic particle with no electric, color, or weak charge, that would mean it behaves as its own antiparticle.

If you can collect two dark matter particles and make them interact with one another, there's a finite probability that they'll annihilate. When an annihilation occurs, they'll produce pure energy in a 100% efficient fashion: via Einstein's E = mc 2 . In other words, if we understand dark matter correctly, there's a free, unlimited source of energy everywhere humanity dreams of going.

The XENON experiment located underground in the Italian LNGS laboratory. The detector is installed . [+] inside a large water shield the building next to it accommodates its various auxiliary subsystems. If we can understand and measure the particle properties of dark matter, we may be able to create conditions that coax it into annihilating with itself, leading to the release of energy via Einstein's E=mc^2, and the discovery of a perfect spacecraft fuel.

Because dark matter is everywhere, we wouldn't even need to carry it with us as we traversed the Universe. As far as we understand it — and admittedly, we need to understand it a lot farther — dark matter could truly deliver our dream of the ultimate fuel. It's abundant all throughout our galaxy and beyond it should have a non-zero annihilation cross-section with itself and when it does annihilate, it should produce energy with 100% efficiency.

Perhaps, then, most of us have been thinking about experiments seeking to directly detect dark matter all wrong. Yes, we want to know what makes up the Universe, and what the physical properties of its various abundant components truly are. But there's a science-fiction dream that could come true if nature is kind to us: unlimited, free energy just waiting there for us to harness, no matter where in the galaxy we go.


Answers and Replies

So far we have no evidence that what is called "dark energy" corresponds to an actual energy.
The simplest explanation is that there is a cosmological curvature constant Λ, which is a constant intrinsic curvature in spacetime (which could have various explanations or simply be a constant of nature).

this curvature Λ does not have to be caused by some mysterious "energy", it is reflected in the observations of how the hubble expansion rate H(t) evolves over time. H(t) seems to be declining but not to zero, it seems to be leveling out at a longterm asymptotic rate we can call H ≈ 1/17.3 percent per million years.
The current expansion rate is H0 = H(now) = 1/14.3 percent per million years. But this has been declining and best fit to the accumulated data indicates H→H.

that is essentially what they mean by "acceleration". the rate is going to a positive rate as limit instead of zero.
growth at a constant positive rate is, of course, exponential, even if the rate is rather slow in percentage terms.

this does not require that space be full of some mysterious "energy"
energy is not required for distances to increase, geometry is dynamic, that has been known for generations.
there is a lot of excited hype surrounding the discovery that the limiting longterm rate is not zero.

Assuming the most common Dark Energy models, it's density remains constant even with the universe expansion. As new space volume is created, it contains the same amount of dark energy as the previously existing space for the same volume unit.

If we assume that at a certain epoch of cosmic time, say 13 billion years elapsed from the Big Bang, the universe is finite in volume and time (we opt to dismiss the block-time view), this means that the amount of dark energy contained in the universe at that epoch is finite.

But if the universe is expanding and accelerating as it is currently mostly believed, it should mean that the expansion will continue forever towards infinity, therefore also Dark Energy will need to be created in infinite quantity.

The rate of expansion doesn't increase. That rate is decreasing and approaching a constant value. This is described as accelerated expansion because if you have a constant rate of expansion (speed per distance), then the distance between objects increases at an accelerating rate.

There is a (rather unphysical) model where precisely what you describe does happen. It's known as the big rip. This isn't normal dark energy, though: it's dark energy where the energy density grows over time. In such a universe, the rate of expansion increases, and yes, it becomes singular in a finite amount of time. This model is almost certainly impossible, however, as it violates all of General Relativity's energy conditions (if you're curious what that means, see the Wikipedia page here.


The 3 Ways That Parallel Universes Could Be Real

A huge number of separate regions where Big Bangs occur are separated by continuously inflating . [+] space in eternal inflation. But unless there's a truly infinite amount of space out there, the number of possible outcomes grows faster than the number of possible Universes like ours.

Karen46 of http://www.freeimages.com/profile/karen46

The idea that things exist in a particular, well-defined state at all times where their properties can be determined so long as you can measure them well enough was fundamental to how we conceived of the Universe. When quantum physics came along, that idea went right out the window, never to return. The Universe, at a fundamental level, is indeterminate. One possible interpretation -- that of infinite parallel Universes -- holds that every time a quantum interaction occurs, all possible outcomes do actually occur somewhere, with only one of them reflecting what happens in our observable Universe. But if the right conditions exist, these parallel Universes will actually be real.

An interference pattern results if you pass electrons, photons or any other particle through a . [+] double slit. But only if you don't check which slit they passed through!

Wikimedia Commons user inductiveload

Quantum indeterminism is a fundamental fact of the Universe, but how we interpret it is up to us. If you fire a single electron through a double slit, you'd like for it to go through either one slit or the other, but that's not how the Universe works. Instead, the electron acts as a wave, passing through both slits simultaneously and interfering with itself. There's a probability distribution describing where each individual electron will wind up, but each one will only make a single "hit" on a background screen. If you take thousands of these electrons in a row, the interference pattern will emerge.

The wave pattern for electrons passing through a double slit, one-at-a-time. If you measure “which . [+] slit” the electron goes through, you destroy the quantum interference pattern shown here. Note that more than one electron is required to reveal the interference pattern.

Dr. Tonomura and Belsazar of Wikimedia Commons

There are lots of processes that are inherently indeterminate in exactly this fashion. Some are discrete: when you collide a particle and antiparticle to create two photons, one of the photons will have spin +1 and the other will have a spin of -1, but which is which has a 50:50 shot. Other indeterminate processes are continuous: colliding a particle and antiparticle creates two photons, and those two photons will be created in opposite directions (oriented 180 degrees) relative to one another in the particle/antiparticle's center-of-mass frame. But what direction will those photons pick? North/South? East/West? Up/Down? Anything in between? It's entirely random.

Particle-antiparticle annihilation will produce two photons of equal energy in opposite directions. . [+] But which direction that will be is completely random.

Every interaction between two particles in the Universe has this quantum indeterminism, at some level, inherent to it. Every particle has an inherent uncertainty to both its position and momentum, and when two of them interacts, that uncertainty propagates into the final position and momentum, too. We have a lot of different ways to try and understand this indeterminism, many of which are equally valid.

The idea of parallel Universes, as applied to Schrödinger's cat.

These interpretations of quantum mechanics cannot be distinguished from one another, and include ideas like wavefunction collapse (where an observation triggers the collapse of the wavefunction), an ensemble approach to possible outcomes (where all outcomes are possible, and the Universe selects one when an observation is made), and the many-worlds approach, where all possible outcomes do occur in some Universe, but we only have the one Universe to observe.

The multiverse idea states that there are infinite numbers of Universes like our own, and infinite . [+] ones with differences.

This last one has a fantastic consequence, if true: there must exist a number of parallel Universes that's so great, it approaches infinity as time goes on. There are some 10^90 particles in the observable Universe, which has been around for 13.8 billion years since the Big Bang, and each particle has undergone anywhere from millions of interactions to many quadrillions (or more) over that time. The number of possible outcomes is ridiculously huge -- a number greater than (10^90)! -- but that doesn't mean the many-worlds approach is ridiculous. In fact, there are a number of ways in which it could be exactly true.

The observable Universe might be 46 billion light years in all directions from our point of view, . [+] but there's certainly more, unobservable Universe, perhaps even an infinite amount, just like ours beyond that.

Frédéric MICHEL and Andrew Z. Colvin, annotated by E. Siegel

1.) The Universe, of which our observable Universe is a small part, was born infinite. No matter how many particles we have in our Universe, no matter how arbitrary their initial configurations and no matter how many possible outcomes their interactions could have given rise to, that number will still be finite. But the Universe could have been born infinite! Beyond the stars, galaxies, matter and energy that we can see, we have every reason to believe that there is more "Universe" just like our own, and that it's simply not observable to us due to the fact that the speed of light and the age of the Universe (since the Big Bang) are both finite. If there's an infinite amount of Universe like this, then the exact configuration starting off our Universe occurred an infinite amount of times, and everything that was ever possible happened somewhere.

Inflation set up the hot Big Bang and gave rise to the observable Universe we have access to, but we . [+] can only measure the last tiny fraction of a second of inflation's impact on our Universe.

Bock et al. (2006, astro-ph/0604101) modifications by E. Siegel

2.) Our Universe was born finite, but there were an infinite number of them born. The Big Bang was not the very beginning of everything, as we once thought, but was merely the birth of our observable Universe. It was the first moment that our Universe could be described as hot, dense, full of matter/antimatter/radiation, and simultaneously expanding and cooling. This happened a finite amount of time ago -- 13.8 billion years -- and was preceded by a period of cosmic inflation. Inflation creates an exponentially growing spacetime, which means, if it occurred for an infinite amount of time to the past, could have created an infinite number of finite Universes, one of which contains ours.

Even though inflation may end in more than 50% of any of the regions at any given time (denoted by . [+] red X’s), enough regions continue to expand forever that inflation continues for an eternity, with no two Universes ever colliding.

3.) Our Universe was born finite, there are a finite number of Universes, but there are enough of them around that all possible outcomes still occur. This is the trickiest case of all, because nothing -- not even exponentially-growing, inflating spacetime -- grows as fast as the number of possible quantum outcomes for the Universe. But a big enough, possibility-rich enough multiverse will have created a Universe with identical initial conditions to our enough times that all the possible outcomes to date have been realized somewhere. This will change, given enough time as interactions continue and quantum systems evolve, we will eventually see the number of possibilities surpass the number of Universes available to realize all of them.

A representation of the different parallel "worlds" that might exist in other pockets of the . [+] multiverse.

Somewhere, the Nazis won World War II somewhere, Hillary Clinton is president somewhere, humans have driven themselves to extinction somewhere, we've achieved world peace. We still have just the one Universe, though, and still have no prospects for gathering information outside of what's observable to us. But if the Universe was born infinite, if the state that gave rise to it existed for an infinite amount of time, or we simply created enough pocket Universes for these parallel Universes to exist today, then they're real. And they could be real if any of these three possibilities are true there are three different paths to success. But until we have some way of testing it, we have no way of knowing what the ultimate truth of the matter is, and whether parallel Universes truly are real.