I What Are the Proposed Alternatives to the Multiverse Theory?

[windy miller]

It has been argued that constants of nature are fine tuned for life. Many in the physics community explain this by a selection effect in the multiverse. However some seem unhappy with this , so what alternatives do they suggest?

 

[newjerseyrunner]

It has been argued that constants of nature are fine tuned for life. Many in the physics community explain this by a selection effect in the multiverse. However some seem unhappy with this , so what alternatives do they suggest?

An alternative is that those finely tuned constants aren't really constants at all and are emergent from something much deeper.

If you mean why are the laws of physics so life-friendly? That's actually easy to explain logically. We exist, therefore, we must exist in a universe that's life-friendly, there is no other way it could have gone.

 

[Flyx]

An alternative is that those finely tuned constants aren't really constants at all and are emergent from something much deeper.

If you mean why are the laws of physics so life-friendly? That's actually easy to explain logically. We exist, therefore, we must exist in a universe that's life-friendly, there is no other way it could have gone.

A fan of the Weak Anthropic Principle, I see

 

[newjerseyrunner]

A fan of the Weak Anthropic Principle, I see

I don't like that term, anthropic implies human beings. I prefer to think of it like this: An entity must exist within a universe that permits it to exist. Super Mario can not exist in our universe, and we can't exist in his.

 

[windy miller]

An alternative is that those finely tuned constants aren't really constants at all and are emergent from something much deeper.

If you mean why are the laws of physics so life-friendly? That's actually easy to explain logically. We exist, therefore, we must exist in a universe that's life-friendly, there is no other way it could have gone.

Thanks, ay references that flesh out the constants aren't really constant idea?

 

[rootone]

The whole multiverse thing, (which I personally am not happy with), implies that what we take to be constants in our observable universe may have different values in other variations of the Universe.
So the argument goes that we exist in this variation of the Universe because carbon based life is possible given our local Universe's parameter set.
The concept falls out of string theory and 'other unseen dimensions'.
I am not happy one bit with that - because something being 'beautiful' mathematically does not make it true.
However some do like that kind of thing.
If somebody rambled on to me about unseeable dimensions without the clever math, I would think they were nuts.

 

[Chalnoth]

It has been argued that constants of nature are fine tuned for life. Many in the physics community explain this by a selection effect in the multiverse. However some seem unhappy with this , so what alternatives do they suggest?

The difficult thing with this kind of discussion is that it isn't really anchored in data. This makes it so that it largely boils down to personal opinion on what kind of theory is more "natural".

Typically theoretical ideas about how the constants got to be the way they are fall into two broad categories:
1. Physical constants had to take the specific values they take because of physics that we don't yet know.
2. Physical constants can take many possible different values and the constants we observe are largely a result of random chance.

I think that in general most theoretical physicists believe that the correct answer is a mixture of the two, and most of the disagreement comes down to how much option (1) or (2) can explain about our universe.

Until we have solid data, however, there's not likely to be much agreement. Unfortunately that may never be possible.

 

[Chronos]

I am always reminded of the Pi paradox by questions regarding the physical constants: why does Pi have the value it does? If the rules of geometry were just slightly different might Pi assume some other value. Does Pi define the rules of geometry or vice versa? If the former is true, why is Pi so special? I'm of the mind that some things just are what they are and must be what they are to enable a mathematically consistent universe. You only need a small number of fundamental physical 'constants' [perhaps only one] to construct our entire universe if you subscribe to the idea the universe is an emergent phenomenon.

 

[MacRudi]

Anthropic principle always implies, as if the universe was made for us to exist. The same thinking as if evolutionary processes have the goal to make something better to fit. There is no reason for it. There is no goal or design.
We make a Gedanken Experiment:
In String theory it is possible, that we have a universe where quasi particle are fermions or real bosons (forces) and on the other side bosons and fermions are only quasiparticles. Then let the evolution build out of these fermions and bosons atoms and molecules. Something completely different exists and maybe life out of these molecules. They would think in this universe, that there is an anthropic principle too, that their universe was designed for them.
A Universe can be slightly different, that maybe all trees look yellow and not green. But it is possible to live in it and evolution can happen also.
What we call now our perfect universe designed for us, doesn't have to really be the best of all possibilities.
The multiverse theory let us give the possibility to define constants out of some field equations. Constants are not there because they are there without any explanation and god given. That's the big advantage of multiversetheory.
If we have in truth a multiverse is another question. It let's explain the big bang as a smash of 2 branes. Another advantage.
If we need a multiverse theory for explanation? Yes!
If we really live in a multiverse? no one knows.
Is it important? not really (up to now)

 

[newjerseyrunner]

Anthropic principle always implies, as if the universe was made for us to exist.

No it doesn't. It just says that a universe that includes sentient beings must have laws that allow those beings to exist. There is no concept of purpose. The anthropic principle is perfectly valid assuming that there is no purpose and we are a cosmic accident.

There are two variables, whether or not sentient beings exist and whether or not the universe allows it.
If the universe allows sentient beings either of these two statements can be true

1. There is sentient life in the universe
2. There is no sentient life in the universe

However, in a universe that does not allow for sentient life the only possibility is

1. There is no sentient life in the universe

No purpose.Us existing and the universe not allowing sentience are mutually exclusive.

 

[MacRudi]

No it doesn't. It just says that a universe that includes sentient beings must have laws that allow those beings to exist. There is no concept of purpose. The anthropic principle is perfectly valid assuming that there is no purpose and we are a cosmic accident.

But most people think of it like this. The same with religious people who want to believe, that evolution is equal to genesis in bible.

 

[windy miller]

Anthropic principle always implies, as if the universe was made for us to exist. The same thinking as if evolutionary processes have the goal to make something better to fit. There is no reason for it. There is no goal or design.
We make a Gedanken Experiment:
In String theory it is possible, that we have a universe where quasi particle are fermions or real bosons (forces) and on the other side bosons and fermions are only quasiparticles. Then let the evolution build out of these fermions and bosons atoms and molecules. Something completely different exists and maybe life out of these molecules. They would think in this universe, that there is an anthropic principle too, that their universe was designed for them.
A Universe can be slightly different, that maybe all trees look yellow and not green. But it is possible to live in it and evolution can happen also.
What we call now our perfect universe designed for us, doesn't have to really be the best of all possibilities.
The multiverse theory let us give the possibility to define constants out of some field equations. Constants are not there because they are there without any explanation and god given. That's the big advantage of multiversetheory.
If we have in truth a multiverse is another question. It let's explain the big bang as a smash of 2 branes. Another advantage.
If we need a multiverse theory for explanation? Yes!
If we really live in a multiverse? no one knows.
Is it important? not really (up to now)

Thank you of your reply. Just to correct you, in cosmology today the multiverse si mostly associated with eternal inflation. The crashing branes is a different model to inflation, in fact it is supposed to be an alternative to inflation.

 

[MacRudi]

Thank you of your reply. Just to correct you, in cosmology today the multiverse si mostly associated with eternal inflation. The crashing branes is a different model to inflation, in fact it is supposed to be an alternative to inflation.

There are different and many possibilities. Eternal Inflation of Andre Linde is one side of many aspects. Superstring theory has other options as M Theory etc.

 

[eloheim]

From my perspective, generally, having to resort to anthropic explanations isn't anyone's ideal. If that's what you're left with though, the strength of the case should come down to what science should come down to anyway: Quatification!

Saying "strong anthropic scenarios favor a sub-GUT scale cosmological constant, so that structure has time to evolve" isn't equivalent to having a motivated, plausible (and hopefully specific) mechanism that dictates (e.g.) the range and distribution of C.C. values across universes, and makes a genuine quantified prediction for what someone (some-thing?!) in a typical life-permitting universe will be likely to see.

A lot of skeptics will (rightly, I might add) be wary of any imperfect/non-ideal mode of explanation in physics, especially when retrofitting of theories and parameters are possible. IMO such caution is justified, but if an anthropic explanation can meet the criteria mentioned above (such as quantified expectation confidence/measurement uncertainty/etc.) at least the unappealing pill would be a bit less bitter to swollow!

 

[windy miller]

Thanks you for your replies. But a lot of them seem to be not the original question The thread is not intended to be a debate about the plusses of minuses of a multiverse but to ask what other scientific alternatives there are to explain why the constants of nature take the values they do.

 

[Chronos]

The short answer is we don't know why things like the fine structure constant is 1/137 nor why it assumes its particular value. Nothing in our theories accounts for any natural constant assuming the value it is possesses. Theoretical physicists reserve use of the term fundamental physical constant for dimensionless physical constants that cannot be derived by any means other than empirical. One of the grand goals of physics is to achieve a TOE [theory of everything] which would enable us to calculate the fundamental constants from first principles. Of course, any such derived constants would no longer qualify as fundamental and be replaced by whatever 'first principle' enabled them to be calculated. A 'first principle is classically defined as a self-evident proposition or assumption that cannot be deduced from any other proposition or assumption.

 

[windy miller]

The short answer is we don't know why things like the fine structure constant is 1/137 nor why it assumes its particular value. Nothing in our theories accounts for any natural constant assuming the value it is possesses. Theoretical physicists reserve use of the term fundamental physical constant for dimensionless physical constants that cannot be derived by any means other than empirical. One of the grand goals of physics is to achieve a TOE [theory of everything] which would enable us to calculate the fundamental constants from first principles. Of course, any such derived constants would no longer qualify as fundamental and be replaced by whatever 'first principle' enabled them to be calculated. A 'first principle is classically defined as a self-evident proposition or assumption that cannot be deduced from any other proposition or assumption.

I seem to have found an alternative:
http://arxiv.org/abs/1009.5514
perhaps the vary as some scalar field

 

[Chalnoth]

I seem to have found an alternative:
http://arxiv.org/abs/1009.5514
perhaps the vary as some scalar field

There's lots and lots of ideas like this floating around.