Posted on **02/20/2015 6:01:20 PM PST** by **LibWhacker**

Infinity Is a Beautiful Concept – And It’s Ruining Physics

I was seduced by infinity at an early age. Georg Cantor’s diagonality proof that some infinities are bigger than others mesmerized me, and his infinite hierarchy of infinities blew my mind. The assumption that something truly infinite exists in nature underlies every physics course I’ve ever taught at MIT—and, indeed, all of modern physics. But it’s an untested assumption, which begs the question: Is it actually true?

There are in fact two separate assumptions: “infinitely big” and “infinitely small.” By infinitely big, I mean that space can have infinite volume, that time can continue forever, and that there can be infinitely many physical objects. By infinitely small, I mean the continuum—the idea that even a liter of space contains an infinite number of points, that space can be stretched out indefinitely without anything bad happening, and that there are quantities in nature that can vary continuously.

The two assumptions are closely related, because inflation, the most popular explanation of our Big Bang, can create an infinite volume by stretching continuous space indefinitely. The theory of inflation has been spectacularly successful and is a leading contender for a Nobel Prize. It explains how a subatomic speck of matter transformed into a massive Big Bang, creating a huge, flat, uniform universe, with tiny density fluctuations that eventually grew into today’s galaxies and cosmic large-scale structure—all in beautiful agreement with precision measurements from experiments such as the Planck and the BICEP2 experiments. But by predicting that space isn’t just big but truly infinite, inflation has also brought about the so-called measure problem, which I view as the greatest crisis facing modern physics.

Physics is all about predicting the future from the past, but inflation seems to sabotage this. When we try to predict the probability that something particular will happen, inflation always gives the same useless answer: infinity divided by infinity. The problem is that whatever experiment you make, inflation predicts there will be infinitely many copies of you, far away in our infinite space, obtaining each physically possible outcome; and despite years of teeth-grinding in the cosmology community, no consensus has emerged on how to extract sensible answers from these infinities. So, strictly speaking, we physicists can no longer predict anything at all!

This means that today’s best theories need a major shakeup by retiring an incorrect assumption. Which one? Here’s my prime suspect: ∞.

A rubber band can’t be stretched indefinitely, because although it seems smooth and continuous, that’s merely a convenient approximation. It’s really made of atoms, and if you stretch it too far, it snaps. If we similarly retire the idea that space itself is an infinitely stretchy continuum, then a big snap of sorts stops inflation from producing an infinitely big space and the measure problem goes away. Without the infinitely small, inflation can’t make the infinitely big, so you get rid of both infinities in one fell swoop—together with many other problems plaguing modern physics, such as infinitely dense black-hole singularities and infinities popping up when we try to quantize gravity.

In the past, many venerable mathematicians were skeptical of infinity and the continuum. The legendary Carl Friedrich Gauss denied that anything infinite really exists, saying “Infinity is merely a way of speaking” and “I protest against the use of infinite magnitude as something completed, which is never permissible in mathematics.” In the past century, however, infinity has become mathematically mainstream, and most physicists and mathematicians have become so enamored with infinity that they rarely question it. Why? Basically, because infinity is an extremely convenient approximation for which we haven’t discovered convenient alternatives.

Consider, for example, the air in front of you. Keeping track of the positions and speeds of octillions of atoms would be hopelessly complicated. But if you ignore the fact that air is made of atoms and instead approximate it as a continuum—a smooth substance that has a density, pressure, and velocity at each point—you’ll find that this idealized air obeys a beautifully simple equation explaining almost everything we care about: how to build airplanes, how we hear them with sound waves, how to make weather forecasts, and so forth. Yet despite all that convenience, air of course isn’t truly continuous. I think it’s the same way for space, time, and all the other building blocks of our physical world.

Let’s face it: Despite their seductive allure, we have no direct observational evidence for either the infinitely big or the infinitely small. We speak of infinite volumes with infinitely many planets, but our observable universe contains only about 10^{89} objects (mostly photons). If space is a true continuum, then to describe even something as simple as the distance between two points requires an infinite amount of information, specified by a number with infinitely many decimal places. In practice, we physicists have never managed to measure anything to more than about seventeen decimal places. Yet real numbers, with their infinitely many decimals, have infested almost every nook and cranny of physics, from the strengths of electromagnetic fields to the wave functions of quantum mechanics. We describe even a single bit of quantum information (qubit) using two real numbers involving infinitely many decimals.

Not only do we lack evidence for the infinite but we don’t need the infinite to do physics. Our best computer simulations, accurately describing everything from the formation of galaxies to tomorrow’s weather to the masses of elementary particles, use only finite computer resources by treating everything as finite. So if we can do without infinity to figure out what happens next, surely nature can, too—in a way that’s more deep and elegant than the hacks we use for our computer simulations.

Our challenge as physicists is to discover this elegant way and the infinity-free equations describing it—the true laws of physics. To start this search in earnest, we need to question infinity. I’m betting that we also need to let go of it.

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To: **LibWhacker**

Physicist don’t have a clue here.

To: **SunkenCiv**

Of interest Ping

3
posted on **02/20/2015 6:02:43 PM PST**
by left that other site
(You shall know the Truth, and The Truth Shall Set You Free.)

To: **LibWhacker**

Infinity wrecks hell too.

To: **LibWhacker**

Infinity cannot be bound by Time and it cannot be bound by Space.

Something that transcends, or is outside Time and Space ... hmmmmmmmm ... wherever could this take us?

Something that transcends, or is outside Time and Space ... hmmmmmmmm ... wherever could this take us?

And can Science help us to understand something outside Time and Space? Nope.

5
posted on **02/20/2015 6:05:34 PM PST**
by ClearCase_guy
(The dog days are over /The dog days are done/Can you hear the horses? /'Cause here they come)

To: **dragnet2**

Sounds like this right here:

is either a semantical faux pas or rank contradiction.that time can continue forever

To: **LibWhacker**

““infinitely small.”

I think he forgot, “Finitely small”. ;-)

7
posted on **02/20/2015 6:08:10 PM PST**
by spel_grammer_an_punct_polise
(Why does every totalitarian, political hack think that he knows how to run my life better than I do?)

To: **9thLife**

I never suggested that regarding time, my comment was physicist have no clue here.

What we do understand about the universe/infinity etc, has stood physics on it’s head.

To: **LibWhacker**

How brilliant -— If I can’t understand it and it confuses me, it doesn’t exist.

That can be used to “solve” all sorts of problems...just make them go away.

To: **LibWhacker**

infinity / infinity = unity.

10
posted on **02/20/2015 6:12:36 PM PST**
by central_va
(I won't be reconstructed and I do not give a damn.)

To: **LibWhacker**

A word used often without understanding the consequences of believing it.

Like saying God is infinite but then saying He doesn’t care about some (to us) ‘minor’ detail.

To: **dragnet2**

Physicists claim to be in search of the truth, but they are really only in search of equations that predict future measurements.

They are the ultimate pragmatists, but are unwilling to fess up to this.

To do so would lower their status to that of mere engineers.

To: **LibWhacker**

Things such as infinity, singularities, or discontinuities, are mathematical concepts. Mathematics allows two dimensional worlds, or 8 dimensional worlds, and many other things that are not possible in a physical world. Physicists often use mathematics to describe the physical world, but the match is not always exact. So what? That doesn’t mean either is wrong, they just are not exactly right.

13
posted on **02/20/2015 6:14:27 PM PST**
by norwaypinesavage
(The Stone Age did not end because we ran out of stones)

To: **central_va**

{No. of Real Numbers}/{No. of Rational Numbers} does not equal 1

To: **9thLife**

God is the only true infinity. Every other theory of infinity is only human arrogance speaking.

To: **House Atreides**

The atheist's creed.

16
posted on **02/20/2015 6:15:10 PM PST**
by ClearCase_guy
(The dog days are over /The dog days are done/Can you hear the horses? /'Cause here they come)

To: **LibWhacker**

wait a second right there! What about EBT cards, welfare, EITC, social security...any government program! they go on for all time and continuously expand toward infinity.

17
posted on **02/20/2015 6:15:24 PM PST**
by ProtectOurFreedom
(For those who understand, no explanation is needed. For those who do not, no explanation is possible)

To: **LibWhacker**

Any true beauty in the universe is proof of Gd. And infinity is too beautiful a concept to give up.

To: **norwaypinesavage**

Mathematicians and scientists get jobs, awards, and honors when they come up with theories that are closer approximations to what we hope is "exactly right".

To: **Ciexyz**

Whether or not Cantor was arrogant, when he came up with his theories regarding infinity it was not just arrogance speaking. There was a heckuva lot of math and logic as well.

first

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