Posted on 10/13/2015 11:04:06 PM PDT by LibWhacker
The Universe Never Expands Faster Than the Speed of Light
Breaking my radio silence here to get a little nitpick off my chest: the claim that during inflation, the universe “expanded faster than the speed of light.” It’s extraordinarily common, if utterly and hopelessly incorrect. (I just noticed it in this otherwise generally excellent post by Fraser Cain.) A Google search for “inflation superluminal expansion” reveals over 100,000 hits, although happily a few of the first ones are brave attempts to squelch the misconception. I can recommend this nice article by Tamara Davis and Charlie Lineweaver, which tries to address this and several other cosmological misconceptions.
This isn’t, by the way, one of those misconceptions that rattles around the popular-explanation sphere, while experts sit back silently and roll their eyes. Experts get this one wrong all the time. “Inflation was a period of superluminal expansion” is repeated, for example, in these texts by by Tai-Peng Cheng, by Joel Primack, and by Lawrence Krauss, all of whom should certainly know better.
The great thing about the superluminal-expansion misconception is that it’s actually a mangle of several different problems, which sadly don’t cancel out to give you the right answer.
1.The expansion of the universe doesn’t have a “speed.” Really the discussion should begin and end right there. Comparing the expansion rate of the universe to the speed of light is like comparing the height of a building to your weight. You’re not doing good scientific explanation; you’ve had too much to drink and should just go home.The expansion of the universe is quantified by the Hubble constant, which is typically quoted in crazy units of kilometers per second per megaparsec. That’s (distance divided by time) divided by distance, or simply 1/time. Speed, meanwhile, is measured in distance/time. Not the same units! Comparing the two concepts is crazy.
Admittedly, you can construct a quantity with units of velocity from the Hubble constant, using Hubble’s law, v = Hd (the apparent velocity of a galaxy is given by the Hubble constant times its distance). Individual galaxies are indeed associated with recession velocities. But different galaxies, manifestly, have different velocities. The idea of even talking about “the expansion velocity of the universe” is bizarre and never should have been entertained in the first place.
2. There is no well-defined notion of “the velocity of distant objects” in general relativity. There is a rule, valid both in special relativity and general relativity, that says two objects cannot pass by each other with relative velocities faster than the speed of light. In special relativity, where spacetime is a fixed, flat, Minkowskian geometry, we can pick a global reference frame and extend that rule to distant objects. In general relativity, we just can’t. There is simply no such thing as the “velocity” between two objects that aren’t located in the same place. If you tried to measure such a velocity, you would have to parallel transport the motion of one object to the location of the other one, and your answer would completely depend on the path that you took to do that. So there can’t be any rule that says that velocity can’t be greater than the speed of light. Period, full stop, end of story.
Except it’s not quite the end of the story, since under certain special circumstances it’s possible to define quantities that are kind-of sort-of like a velocity between distant objects. Cosmology, where we model the universe as having a preferred reference frame defined by the matter filling space, is one such circumstance. When galaxies are not too far away, we can measure their cosmological redshifts, pretend that it’s a Doppler shift, and work backwards to define an “apparent velocity.” Good for you, cosmologists! But that number you’ve defined shouldn’t be confused with the actual relative velocity between two objects passing by each other. In particular, there’s no reason whatsoever that this apparent velocity can’t be greater than the speed of light.
Sometimes this idea is mangled into something like “the rule against superluminal velocities doesn’t refer to the expansion of space.” A good try, certainly well-intentioned, but the problem is deeper than that. The rule against superluminal velocities only refers to relative velocities between two objects passing right by each other.
3. There is nothing special about the expansion rate during inflation. If you want to stubbornly insist on treating the cosmological apparent velocity as a real velocity, just so you can then go and confuse people by saying that sometimes that velocity can be greater than the speed of light, I can’t stop you. But it can be — and is! — greater than the speed of light at any time in the history of the universe, not just during inflation. There are galaxies sufficiently distant that their apparent recession velocities today are greater than the speed of light. To give people the impression that what’s special about inflation is that the universe is expanding faster than light is a crime against comprehension and good taste.
What’s special about inflation is that the universe is accelerating. During inflation (as well as today, since dark energy has taken over), the scale factor, which characterizes the relative distance between comoving points in space, is increasing faster and faster, rather than increasing but at a gradually diminishing rate. As a result, if you looked at one particular galaxy over time, its apparent recession velocity would be increasing. That’s a big deal, with all sorts of interesting and important cosmological ramifications. And it’s not that hard to explain.
But it’s not superluminal expansion. If you’re sitting at a stoplight in your Tesla, kick it into insane mode, and accelerate to 60 mph in 3.5 seconds, you won’t get a ticket for speeding, as long as the speed limit itself is 60 mph or greater. You can still get a ticket — there’s such a thing as reckless driving, after all — but if you’re hauled before the traffic judge on a count of speeding, you should be able to get off scot-free.
Many “misconceptions” in physics stem from an honest attempt to explain technical concepts in natural language, and I try to be very forgiving about those. This one, I believe, isn’t like that; it’s just wrongity-wrong wrong. The only good quality of the phrase “inflation is a period of superluminal expansion” is that it’s short. It conveys the illusion of understanding, but that can be just as bad as straightforward misunderstanding. Every time it is repeated, people’s appreciation of how the universe works gets a little bit worse. We should be able to do better.
I think it would be pretty cool to watch your family tree backwards to see how your personal family history fits into the entire human race.
Infinite thanks for the article and your esoteric insight.
The Universe will never cease to be a source of inexplicable wonder.
Don’t tell the Enterprise crew(s) that FTL travel is impossible.
The ship doesn’t move. Space does.
Or, the objects didn't move at all, but the underlaying spacetime between the objects has expanded. Kind of like objects orbiting the Earth aren't traveling in a circle, spacetime around the planet is curved. Objects are traveling in a straight line thru spacetime, which is curved.
I can see that.
[[I’m not even going to pretend I understand this, but I have a question. If two things left the point of the singularity in opposite directions traveling at the speed of light for 13.8 billion years, wouldn’t they now be 27.6 billion light years apart?]]
Depends on how much headwind they run into
Serious question, asked out of complete ignorance: could we measure it if the universe did expand faster than light? How?
All of money given to Jeb has also gone into a wormhole.
Iron Maiden has a new album...first song...SPEED OF LIGHT!
For older rockers...they sounded great.
Once we were convinced the universe revolved around the earth. All the educated, tested, scientific guesses made today that seem logical, rational, prudent and backed by “the evidence” could quite possibly be relegated as primitive, imaginative ponderings at some point in the future.
Anyone who claims they have a definitive understanding of who/what/where/when/why or how the universe was formed - I admire their optimism!
Two other views on this that come to the same conclusion.
There are two creation stories in Genesis for a reason. The first describes the creation of the universe out of nothing from the beginning. The second describes the creation of Adam and Eve who start CotU’s salvation plan for the creatures that He created. So we can have an “old” universe and a “young” salvation plan at the same time. We will first focus on the creation of the universe out of nothing from the beginning over what we would measure as a long time.
This concept is supported by the Scriptures, and is also supported by the writings of the Hebrew sages:
“According to the master Kabbalists, Rabbi Isaac of Acco, when counting the years of these [7000 year] cycles, one must not use an ordinary physical year, but rather, a divine year. The Midrash says that each divine day is a thousand years, basing this on the verse, “A thousand years in Your sight are as but yesterday” (Psalms 90: 4). Since each year contains 365 1/4 days, a divine year would be 365,250 years long. According to this, each cycle of seven thousand divine years would consist of 2,556,750,000 earthly years. This figure of two-and-a-half billion years is very close to the scientific estimate as to the length of time that life has existed on earth. If we assume that the seventh cycle began with the Biblical account of creation, then this would have occurred when the universe was 15,340,500,000 years old. This is very close to the scientific estimate that the expansion of the universe began some fifteen billion years ago.”
Kaplan, Aryeh (2004-03-15). Sefer Yetzirah: The Book of Creation in Theory and Practice (Kindle Locations 3552-3559). Red Wheel Weiser. Kindle Edition.
‘During the six days of creation described in the first chapter, G-d did not actually create the world, but rather, created the ingredients which would allow the world to develop. It thus refers to the creation of all matter, along with space and time. It was during these six days that G-d brought the universe into being from absolute nothingness. After these six days of creation, G-d allowed the universe to develop by itself, renewing His creation each seven thousand divine years or 2.5 billion earthly years. All the laws of nature and the properties of matter had been fixed for all time, as it is written, “He has established them forever; He has made a decree which shall not be transgressed” (Psalms 148: 6). It is similarly written, “Whatever G-d decrees shall be forever; nothing shall be added to it, and nothing shall be taken away” (Ecclesiastes 3: 14). ‘
Kaplan, Aryeh (2004-03-15). Sefer Yetzirah: The Book of Creation in Theory and Practice (Kindle Locations 3564-3572). Red Wheel Weiser. Kindle Edition.
Rabbi Acco made this calculation, based on the Torah, sometime between 1250 AD and 1340 AD more than 300 years before Sir Isaac Newton was born, and at least 600 years before Edwin Hubble proposed his theory of the expanding universe. The reason aligning the start of the seventh cycle of divine years with the second creation story is based on the rabbinical analysis described in Sefer Yetzirah: The Book of Creation in Theory and Practice. Suffice it to say, but the rabbis could not have been adjusting their analysis to conform the yet to be determined modern scientific value!
More than 600 years ago, the Holy Scriptures, as analyzed by people who really cared about finding the truth in them, reveal the age of the universe we can observe today.
Burkhard Heim arrived at a description of “the beginning” from the currently observed universe using logic and mathematics. He described the process he used in a presentation to the scientists at Messerschmitt-Bölkow-Blohm (MBB) in Ottoburnn, Germany on November 25, 1976. An annotated transcript of the presentation and an English translation was produced by Olar Posdzech, Jim Graham, John Reed and Wilfried Kugel between 2000 and 2009. In this presentation, Heim derived the fundamental quantum of area which he called a “metron”.
In 1992, Tamar Auerbach explained the cosmology of Heim’s Theory as follows:
“In Heim’s theory both the metronic size, t, and the largest diameter D depend on the age of the universe. The dependence is such that D is expanding and t is contracting, so that D was smaller in the past and t was larger. It stands to reason that at one time in the distant past the surface area of a sphere of diameter D in our 3-dimensional world was equal to the size of t. This instant marks the origin of the universe and of time.
The mathematical relation between D and t is not simple, so that 3 different values of D are found to satisfy the criterion that the area of a sphere of diameter D be equal to t at the beginning of time. Evidently, the universe started as a trinity of spheres, whose diameters turn out to be (in meters):
D1 = 0.90992 m, D2 = 1.06426 m, D3 = 3.70121 m.
This trinity of spheres has important bearings on the structure of elementary particles.
From the first moment the universe began to expand, though at a slower rate than is presently predicted on the basis of the red shift of distant galaxies. Heim’s theory results in a present age of the universe approximately equal to 5.45 x 10^107 years, and a diameter D of about 6.37 x 10^109 light years. During most of its existence the universe consisted of an empty metronic lattice, whose metrons kept getting smaller as the universe grew larger. Eventually, metrons became small enough for matter to come into existence. This may have occurred some 15-40 billion (10^9) years ago, at which time matter was created throughout the volume of the universe. Hence, according to Heim matter did not originate very soon after a “big bang” explosion but more uniformly in scattered “fire-cracker” like bursts, perhaps of galactic proportions. Spontaneous uniform creation of matter, coupled with the partly attractive and partly repulsive force of gravity mentioned in Section 3 resulted in the observed large-scale galactic structure of the universe. Creation of matter continues to this day, though on a very much reduced scale.”
Heim’s Theory of Elementary Particle Structures, T. Auerbach and Illobrand von Ludwiger published by the Journal of Scientific Exploration, Vol. 6, No. 3, pp. 217-231, 1992
Heim’s Theory then starts in an analogous way to the way the Hebrew Sages explain it:
And He created His universe with three books (Sepharim), with text (Sepher) with number (Sephar) and with communication (Sippur).
Kaplan, Aryeh (2004-03-15). Sefer Yetzirah: The Book of Creation in Theory and Practice (Kindle Locations 445-449). Red Wheel Weiser. Kindle Edition.
Now the Sefer Yetzirah is said to be part of the oral Torah, but we don’t know for sure, so it should be treated as commentary. So we must look for a pattern in the Torah that matches Heim’s Theory in order to consider Heim’s theory a match for the first creation story. The amazing thing is that the Torah’s description of the creation of the Nation of Israel fits the pattern of these three spheres (books) and the organization of the dimensions used in Extended Heim Theory.
The other great thing for Heim’s theory is that it allows for Faster Than Light travel. It says that gravitons propagate at 4/3 the speed of light.
It’s all relative.
That alone tells you that yes, speed of light can be exceeded.
Not necessarily. Scientists haven't proven that matter can exceed the speed of light.
Two things, either the original premise that the universe is 13 billion years old is wrong or there is more to the universe that scientists haven't taken into consideration.
That’s a good point. From one side of the circle to the other.
Remember Einstein's deal was that the speed of light is the same for all observers.
A photon can be an observer.
So if photon1 watches photon2 move directly away from it, photon1 will measure photon2's speed to be 'c', not 2c, and after 13.8 billion years, photon1 will therefore say photon2 is 13.8 billion ly away, PROVIDED space is not expanding. But that's just it, space is expanding, and not at a constant rate either.
Now, I've glossed over a lot of things. Why? Because I'm always wrong and always gloss over things I don't understand so that I don't screw up my standing.
The 500-year-old redwood in the painting that was painted in January is not 500 years old. It’s not even a tree.
The entire universe is inside a glass globe sitting on someone’s shelf.
3: The speed of light has not been constant
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