Nima Arkani-Hamed - Are there Extra Dimensions?

Extra dimensions—beyond length, width, height—seem like the stuff of science fiction. What would extra dimensions be like? Is time the fourth dimension? Does string theory require ten or eleven dimensions? Could deep reality be so strange? And, anyway, why would we care?

[uremove]

Nice interview! I love that reality is not just stranger than we imagine, but stranger than we CAN imagine! Seems a pity Physics must hide these extra dimensions in tiny Planck length Calabi-Yau manifolds, or inaccessible Branes... Will we ever be able to set out, like Columbus, (or the Square in Abbot’s “Flatland”) to explore and these 10+ dimensions, or must they remain forever mere possibilities in the imaginations of Physicists? 🥺

[Qdogsman]

People who want to consider the possibility of extra dimensions should learn the mathematical characteristics of manifolds. If you understand that our 3D space (or 4D space-time) is an embedded manifold in a space of higher dimensions, then it is unreasonable to expect to "see" outside of our manifold or that any physical structure in our manifold could interact with anything outside of our manifold depending on the nature of the forces acting in our manifold.



To think about this, drop down a dimension and consider some lower-D manifolds that we can understand. For example, think about the surface of the Earth. That surface is a 2D manifold embedded in our 3D space. The analogy to us 3D beings inhabiting our 3D manifold would be 2D vehicles confined to the surface of the earth. Ships are a crude approximation. They are 3D, but in terms of navigating the oceans, they might as well be 2D. They are confined to the surface of the ocean and can't go above it (or below it unless they sink). Their entire range of motion is essentially in the plane that is tangent to the surface at their location. (One of the mathematical properties of a manifold is that it can be approximated by a "flat" manifold of the same dimension as the manifold we are talking about. That is, if you zoom in anywhere on the manifold, it seems to get flatter and flatter.)



So navigators only need two numbers to fix their position (latitude and longitude) and their compass needs to have only one degree of freedom. (They don't need, or can't use azimuth (unless they are aiming their cannons)).



Now, forces are a different thing. The ship experiences the force of wind, the direction of which has only one degree of freedom. It can blow from any of the compass directions. (Updrafts or downdrafts could also happen but sailors don't try to harness them so we can ignore them.) The force of gravity, however is different from the force of the wind. Gravity acts in a direction not available to the navigators. In fact the direction of gravity is perpendicular to each and every possible direction on the compass. So every component vector of the force of gravity in any of those directions is zero, so that force can't be used to propel the ship. Yet the force is acting everywhere on the ocean. But the force of gravity is indirectly observable to the mariners because it provides the field in which the water waves are propagated, and the mariners experience the waves.



IMHO, one of the biggest mistakes made by scientists is to suppose that if there were astronomically large extra dimensions we should be able to observe or interact with them, and they wonder why we can't. I say it is simply because of the mathematical nature of manifolds and that we are in one.



I think Kaluza was on the right track and Klein screwed the idea up even to this day. There is no need to suppose that the extra dimensions are small at all. So the string theorists, who have talked themselves into believing that the particular Calabi-Yau space (i.e. the special manifolds which admit solutions to Einstein's and Maxwell's field equations) they are trying to find must be one of the curled up ones. I think they would have better luck looking at astronomically large ones, like n-tori for example. But I digress.

[mobiustrip]

Guys, I don't think this copernican magnifying thingy will go much further. We need a new paradigm.

[oposkainaxei]

@closer to truth
Almost all videos have bad sound quality. This is quite disappointing though the content quality of the channel is fantastic.
Could you please please fix that?

[ZenoDay]

‘Maybe, if, can, would, ... possibly. ‘ Why limit the description only to prior experience? “Gravity ‘lives’ everywhere?...” 👍, good one.

[jamesruscheinski]

Could exist in infinitely small slices of past, present and future at same time. Would allow quantum gravity to be dispersed into three spatial dimensions of each (9 total).

[tumpau]

Time doesn't exist so considering time as fourth dimension is negated, next is space and is defined by motion of a body and this is not what one to expect from the mysterious of claiming the existence of fourth dimension. However what has been really forgotten or noticed is the angle beside, length, width, and height, so from this viewpoint then we can call angle is the fourth dimension which without it the other three dimensions are not possible, because it has a tight relation with those threes. One line has two dimensions, two lines has three dimensions, and three lines have four dimensions, now every thing consists of endless combinations of areas, as it is seen in MRI and other technichcs used for seeing through living things and nonliving things.

[monkerud]

Take phase spaces, if indeed the no copy theorem is a good theorem, you need to prove that a phase space of every variable in 3d+t does not enclose all possible phase spaces. Good luck with that 3 is the first number that makes infinite color maps ect. Things change a lot from 2d to 3d that does not change much from 3d to 4d space.

[jamesruscheinski]

Not sure what smallest measurable slice of time is. Would it be planck time? What is planck time, 10 power -40 or something like? If smallest measurable time is even smaller than planck constant, then even quantum gravity could exist in more than one dimension of time at once.

[winstonchang]

It is not if there are extra dimensions but WHY WE EVEN ASK ? We feel ourselves to be in a 3 dimensional world so all our HOW, WHERE, WHEN, WHAT, WHY'S are asked
from an awareness of a 3 dimensional world. Einstein said that imagination is more important than just raw knowledge-information. You need to imagine, say,
what is it like to jog around a coin, a penny, , , , In so imagining, you need to BE SMALL so relatively the penny would be a large track My Cat, Mik, is cute, very charmingly cute,
but when I imagine myself to be a small insect or bird, looking UP at my cat, Mik would be this horrible !!!

[jamesruscheinski]

Maybe planck volume has three small extra spatial dimensions?

[nigeltooby]

SO, because they cant find these dimensions they have to be incredibly tiny and tricky to detect. I'd probably say that about the 3rd dimension if I was a flatland scientist desperate to justfy my 2D world as the practical reality of existence...

[madebyporter]

If you zoomed into a zero dimensional dot, would it become a three dimensional sphere? If you zoomed into a 1 dimensional line, would it become a fourth dimension shape?

[haushofer]

It's simply not true that string theory predicts 10 dimensions. It's also consistent in 2+1 dimensions. He knows that, of course.

[NickGled]

1) How many multiple universes are necessary for every possible tuning to be fine tuned in the right way? 2) How many creators are necessary to do the same? 1) Infinity v's 2) ONE!

[wolfeyes]

Does the Maths of extra dimensions enter into other Mathematical equations even though we haven't proven they exist?
For example, adding the equation of other dimensions into other mathematical models because it solves a particular problem?
If so then it may kind of describe how the universe works but it would also be based on false information being that the other dimensions haven't been proven wouldn't it?

So in a sense, it wouldn't really be telling you how the universe works in a factual way but rather based off of some kind of thought puzzle and not reality.

[treiiezi]

what do you mean big or small dimensions? are you confusing dimension with distance/direction?

[winstonchang]

Question is CAN YOUR CONSCIOUSNESS GO THERE ? WHATEVER DIMENSION IT IS...?

[honeys.kapoor]

Prespective of quantum particle, we are a Quantum Universe which exists everywhere to which no law applies.
We can also say this, parallel universe.
Because, parallel means parallel.

Thinking is a state of consciousness.
No law applies to thinking.

Thinking means, experiencing.work of consciousness.

We are being experienced from the prespective of consciousness.


Death is no such thing, meaningless event.

After death ? We will find overselves in the whole universe as consciousness.

Because, thinking is a state of consciousness.
At the moment we are experiencing through this body.

Creation has no meaning without experience.
Prespective of consciousness whatever is happening is happening in nothingnes.

Past present future running in nothingness.

Because, no law applies to consciousness.

The universe (form of quantum reyality) is experiencing itself.



Whatever happens in the world is at the will of humans.
Our prayer are fulfilled through God, this too is the thinking of humans.
Prayer=form of think, state of universe.



Those species which are not in the stage of advance intellect, their desires come out in the form of energy, so their desires are fulfilled.
Hunger, sex extra



Thinking is a state of consciousness.
Please recognize your thinking ability

[monkerud]

Well these arguments are very badly subjective, you cannot say such things. Exstra dimentioms should be necessary if we put them in, the problem is that we dont know every possible 3d+t theoretical framework... so solving a problem is kind of redundant reasoning for justifying it.