# F theory & M theory

• MathematicalPhysicist
In summary: I still think that the future might exist. It's just that we can't know for sure.Originally posted by MajinVegeta We don't know that the future doesn't exist anymore than we know the past has ceased to exist. We only know what our perceptions tells us and, unfortunately, we only perceive a single slice of time. I see. Thank you for your input.In summary, the two theories have a connection but it is not clear what it is.

#### MathematicalPhysicist

Gold Member
what is the relation between the two theories (if there is a connection between them)?

I haven't even heared of the F-Theory. Do you know anything about it?

I haven't heard of F-theory either. I know some of M-theory, but perhaps someone should fill us in on what F-theory is.

F is for "father". It seems to be a 12D string theory that has 2 time dimensions. I'll see if I have any links.

Originally posted by Eh
F is for "father". It seems to be a 12D string theory that has 2 time dimensions. I'll see if I have any links.

2 time dimensions?! That just isn't logical. If everything takes place at a certain point in time, then every spatial point corresponds to a point in time. Does this reasoning allow for another time dimension?

That Net Advance of Physics from the "Physics Napster" topic links to this: abstract. Have fun wading through that.

Does anyone have any information on why a theory would even want to incorporate two dimensions of time?

So, 2 time dimensions would mean two directions of entropy! how cool is that?? Any way, Mentat, I was wondering the same thing.

An idea:
Could two time dimensions allow for the future and the past to exist at the same time? Then, time travel to the past could make sense without breaking the first law of thermodynamics. If someone went to the past, the energy/mass of the universe will remain the same, because the person who went to the past would exist in the future. Since both the future and the past exist, energy/mass is not being lost.

Originally posted by MajinVegeta
An idea:
Could two time dimensions allow for the future and the past to exist at the same time? Then, time travel to the past could make sense without breaking the first law of thermodynamics. If someone went to the past, the energy/mass of the universe will remain the same, because the person who went to the past would exist in the future. Since both the future and the past exist, energy/mass is not being lost.

It couldn't allow for our future and our past to exist at the same time.

There is some appeal that I can gather from the idea of there being two time dimensions: If there are two time dimensions, then "Pretzeled Time" is possible.

Originally posted by MajinVegeta
So, 2 time dimensions would mean two directions of entropy! how cool is that??

You mean, "how impossible is that?", don't you? Entropy can't go in more than one direction, it isn't logical (or at least doesn't seem to be).

Okay, back to the drawing board...

Originally posted by Mentat
You mean, "how impossible is that?", don't you? Entropy can't go in more than one direction, it isn't logical (or at least doesn't seem to be).

why?

Ok..well..entropy is a NET effect...like on our planet...tons of stuff decreases entropy...but the NET effect on the whole universe is that it goes up...

can you be more detailed?

Hm..I don't know the details but I am just providing a general idea...but ok i just realized with 2 time dimensions i have no clue what would be going on...because time as we know it is in one dimension and we can't even imagine what would happen if there were 2 "times"..

do you agree that the future might already exist? i think it makes sense, as it solves the paradox involved with time travel to the past.

Originally posted by MajinVegeta
why?

Because entropy is one effect. It cannot both be increasing and decreasing at the same time, can it? This would be self-contradictory/paradoxical.

Originally posted by MajinVegeta
do you agree that the future might already exist? i think it makes sense, as it solves the paradox involved with time travel to the past.

Think of the terms you're using, Majin. You are using the term "future", which is any point in time that has not already come into existence. This means that the future cannot "already exist", by definition.

You are using the term "future", which is any point in time that has not already come into existence.

We don't know that the future doesn't exist anymore than we know the past has ceased to exist. We only know what our perceptions tells us and, unfortunately, we only perceive a single slice of time.

Or as Richard Feynman said:

It may prove useful in physics to consider events in all of time at once and to imagine that we at each instant are only aware of those that lie behind us.

Who knows?

Originally posted by Mentat
Think of the terms you're using, Majin. You are using the term "future", which is any point in time that has not already come into existence. This means that the future cannot "already exist", by definition.

Yes, I have considered that. But in order to actually make time travel feasible, the past/future should already exist. Mentat, consider a closed time loop for example. If I go to the past(from the future), then my going to the past, would have already happened in the future. So, it creates a kind of closed time loop. So the future, could already exist, and the past as well.

Originally posted by Mentat
Because entropy is one effect. It cannot both be increasing and decreasing at the same time, can it? This would be self-contradictory/paradoxical.

Mentat, the increasing of entropy in two directions could be constant. It does not have to be increasing and decreasing.

Then, time travel to the past could make sense without breaking the first law of thermodynamics

What has the first law of thermodynamics got to do with anything. To recap the first law of thermodynamics is;

The internal energy of a system tends to increase if energy is added via heat and tends to decrease if energy is lost via work done to the system.

Originally posted by Zefram
We don't know that the future doesn't exist anymore than we know the past has ceased to exist. We only know what our perceptions tells us and, unfortunately, we only perceive a single slice of time.

Or as Richard Feynman said:

It may prove useful in physics to consider events in all of time at once and to imagine that we at each instant are only aware of those that lie behind us.

Who knows?

The use of the words "future" and "past" do not, by definition, allow them to "all exist at the same time". Sure, it would be useful to consider them as such. But the words used do not allow for it.

Originally posted by MajinVegeta
If I go to the past(from the future)...

This is where the problem lies. If you go to the past, then the "past" has to currently exist, making it the "present". Thus, you wouldn't be traveling to the "past". In fact, since it takes a certain amount of time to get to the point that you might consider "the past" you are actually traveling to the future.

Originally posted by MajinVegeta
Mentat, the increasing of entropy in two directions could be constant. It does not have to be increasing and decreasing.

You say that the increasing of entropy doesn't have to be increasing?

The use of the words "future" and "past" do not, by definition, allow them to "all exist at the same time". Sure, it would be useful to consider them as such. But the words used do not allow for it.

I doubt the universe is bothered much by semantics.

Past and future in this sense refer (obviously) to a location in time (say, if you were assigning coordinates to something); "events in all of time at once" means that all possible coordinates you could assign to an event do in fact exist (as opposed to some coming into existence at some later time, whatever that would mean). Which means yesterday and tomorrow would both be in existence, even if we presently can only view a single slice of time and perceive only the particular point in time we are at.

Originally posted by Zefram
I doubt the universe is bothered much by semantics.

Past and future in this sense refer (obviously) to a location in time (say, if you were assigning coordinates to something); "events in all of time at once" means that all possible coordinates you could assign to an event do in fact exist (as opposed to some coming into existence at some later time, whatever that would mean). Which means yesterday and tomorrow would both be in existence, even if we presently can only view a single slice of time and perceive only the particular point in time we are at.

Of course this is always possible, but that would mean that the future is already as set as the past. It would also mean that there infinite amounts of each person, since no point in time can be singled out as indivisible (IOW, there is no such thing as an "instant", because that would last for zero time).

Originally posted by Zefram
I doubt the universe is bothered much by semantics.
Good point!

Originally posted by Mentat
This is where the problem lies. If you go to the past, then the "past" has to currently exist, making it the "present". Thus, you wouldn't be traveling to the "past". In fact, since it takes a certain amount of time to get to the point that you might consider "the past" you are actually traveling to the future.

Yes, I have thought of that as well. And it is exactly why I think it almost tenable to assume we could be in a closed time loop. If we are moving at c in a circular pattern, then we could be in a closed time loop? What do you guys thing about that idea?

But does it take time to go to the past?

Originally posted by Mentat
You say that the increasing of entropy doesn't have to be increasing?

no, it could be increasing in two directions at a constant rate. Like a balloon that is being inflated.

Originally posted by MajinVegeta
no, it could be increasing in two directions at a constant rate. Like a balloon that is being inflated.

Doesn't work that way. Entropy is the level of disorder in a closed system. That level of disorder can increase (meaning that the system gets more and more disorderly), or it can decrease (meaning that the system gets more orderly), but it can't do both at the same time, can it?

Mentat, assume the universe is unbalanced=disorderly. If it is unbalanced, then it could be both at onece. That's what makes it disorderly.

Originally posted by MajinVegeta
Mentat, assume the universe is unbalanced=disorderly. If it is unbalanced, then it could be both at onece. That's what makes it disorderly.

Are you saying that, if it is disorderly, then it can be orderly?

I assume that by "two time dimensions" they mean two timelike dimensions, in the sense that the radial dimension of a black hole is timelike (it forces you to move forward, never backward.) I doubt it's much of anything to worry about and more than likely has nothing to do with entropy.