# B Planck Scale

1. Apr 28, 2017

### oquen

It will take a particle accelerator that size of the solar system or more to peek inside the planck scale.. does this mean the planck scale is a no man's land.. or empty? but for a passing electromagnetic field or strong field.. doesn't it pass thru or touch the planck scale at all?

If it doesn't.. and since space is composed of many tiny planck scale.. how does any field exist at all since the planck made up space? Like how can you walk in the ground but avoiding each air molecular or atoms?

2. Apr 28, 2017

### Drakkith

Staff Emeritus
Does the Earth 'touch' a meter? Not a physical meter-stick or other measuring device, but the scale itself?
No, because the meter is a unit of distance, not a physical object. Similarly, the planck scale (or planck length rather) is a unit of distance just like the meter.
Fields, such as the EM field, are continuous and occupy all of space. There is no distance scale where they simply stop existing. The planck length is just a convenient unit of distance to use in certain circumstances.

Space is not divided into little planck-length segments. General Relativity models space as being part of spacetime, which is represented by a smooth and continuous manifold (something which specifies the geometry of spacetime at every point). Note that when I say that space is smooth and continuous, I mean that in a mathematical sense, meaning that there are no breaks, gaps, holes, or other discontinuities in it (singularities aside). This includes sharp edges or corners like what would be found at the vertex or between two sides of a polygon.

As far as science knows, and certainly as we model it now, there is no distance at which space becomes disjointed or segmented.

3. Apr 28, 2017

### oquen

But physicists report it takes a solar system size particular accelerator to probe the planck scale.. if any electromagnetic field can access or probe it.. then why don't they?

4. Apr 28, 2017

### Drakkith

Staff Emeritus
What they mean is that the interaction of particles/fields with other particles/fields changes as your distance or energy scales change and they want to know how the laws of physics work at this scale. To do that, they need to smash particles together at incredibly high energies, which would require an accelerator far bigger than anything we have now.

5. Apr 28, 2017

### oquen

so the natural electromagnetic field passing through the planck scale can itself momentarily create positron/electron pair inside the planck scale? I'm aware that as the length scale gets smaller.. the wavelength needs to become smaller and you can do it by very powerful energies to satisfy debroglie equation. But the natural electromagnetic field is weak yet can reach the planck scale.. can somebody please elaborate where I may not understand it well? Thank you!

6. Apr 28, 2017

### Drakkith

Staff Emeritus
Fields do not have wavelengths. They exist everywhere. It is the disturbances in these fields, which manifest as waves, that have wavelengths.

7. Apr 28, 2017

### oquen

But the wavelengths part of the electromagnetic field still pass through the planck length.. correct? So it puzzles me quite why physicists have to build solar system size accelerator to send the wavelengths into the planck scale when natural electromagnetic field can do that? What part of the arguments escape me??

8. Apr 28, 2017

### rootone

Electromagnetic wavelength which we can possibly detect with present technology ends with observation of the most energetic 'cosmic rays', or gamma ray bursts.
Nothing we can construct on Earth approaches the ability to reproduce those,
yet their wave length still is a lot longer than Planck scale.

9. Apr 28, 2017

### Drakkith

Staff Emeritus
Because of what I already told you. The interactions between particles and fields changes with distance and energy and we need high-energy colliders to find the way they interact at these high energy scales. For example, at extremely short distances and very high temperatures the protons and neutrons making up nuclei "decompose" and become a quark-gluon plasma. Who knows what happens at even higher energies?

10. Apr 28, 2017

### oquen

Returning to this first reply of yours. Recall Superstring theory describes planck scale as unknown and it may not even contain space. And just like liquid and the atoms inside it. Space can be like the liquid and there are atoms of space which may not contain space. Hence Space is indeed or can be divided into little planck-length segments. I think you know Lee Smolin?

11. Apr 28, 2017

### Drakkith

Staff Emeritus
Unlike GR, superstring theory is not a well accepted way to the universe at this time, so whatever it may say is mostly irrelevant. There are many possible theories that go beyond what GR says, but until we know which one is correct we can't take any of their predictions as fact.

Last edited: Apr 28, 2017
12. Apr 29, 2017

### ChrisVer

There are just so many misconceptions in the initial post that it's almost impossible answering anything.
Particle physics: how do we probe higher energies to search for new physics? At the moment we build accelerators, which accelerate particles to high velocities [energies] and by colliding them we can see what the products of those collisions are; we compare those to our current models and decide whether there's something new or not. Then the point is that the highest energy you can reach depends on the center-of-mass energy of the colliding particles (you can't produce more than you give)... LHC best reach would be of TeV, since the protons collide at 13 (14) TeV center-of-mass energy ... but they are not elementary particles, so the elementary particles such as quarks or gluons will have less than 13 (14)TeV energy...
What does it mean that we need an extremely large accelerator: well the more you accelerate the particles the more difficult it gets to keep bending them inside the accelerator till they reach your desired energy (you need extremely large magnets to do that)... One way to increase the energy would then be to increase the radius of the accelerator... higher radius = less bending needed to keep them inside.
If you have a photon with energy ~ 10^19 GeV , you get what is happening at the planck scale. Otherwise it's like asking why you can't see atoms with your eyes (photon detectors at the visual energies range)...

13. Apr 29, 2017

### nikkkom

It looks like you don't know _why_ a large accelerator is necessary to probe properties of interactions on very short scales.

It's simple, but not often spelled out in pop-sci: high energy corresponds to small distances.

Consider the very first discovered "quantum formula" (by Planck himself): energy of a photon = (Planck constant) * frequency. This means that more energetic photons have higher frequency. Higher frequency means that peaks of electromagnetic wave in this photon are closer together, they are not "smeared" around a large region of space. Low energy photons such as radio waves have huge peak-to-peak distances of centimeteres to meters, while high-energy gamma rays have peaks closer than atom radius. As a result, for a radio wave even a macroscopic metal mesh looks like "solid wall", while gamma rays are used for crystallography.

Low-energy particles (any particles, not only photons) all have their waves "smeared" way too much for probing really small scales particle physicists are interested in. That's why we build accelerators which give us high-energy particles.

14. Apr 29, 2017

### oquen

When we are sending radio waves.. can anything in the planck scale picks it up. The radio waves wavelength is way much larger than the planck scale.. but note some submarines are designed to pick up ELF (Extremely Low Frequency) radio wave. So the planck can pick it up too in principle?

In essence. The planck can spy on us.. but we normally can't spy on the planck because we need wavelengths that can fit inside it and this needs huge particular accelerator to create the necessary energy. Is this a correct way of saying it?

15. Apr 29, 2017

### nikkkom

Picking up a radio wave requires an antenna not much smaller than the wavelength. ELF transmitters are huge installations; subs need to use a very sophisticated processing to pick ELF signals up since they can't afford having multi-kilometer antennas.

Planck-scale receiver trying to detect radiowave is like amoeba trying to detect a tsunami wave by measuring pressure difference across its body.

16. Apr 30, 2017

### oquen

There is a saying "do not mistake the map for the territory".. and i'm kinda confused what is the map and territory in the planck scale.

Let's say spacetime as model is the map. And real space is the territory.
In Loop quantum gravity, it is the spacetime which is the map which has spin networks in the planck scale. And real space is the territory. So someday if we can probe planck scale for instance directing gamma ray burst to the target sensors. Can we see loops or strings which are located in the maps or the territory which hasn't got this? Or are the spin networks in LQG located in the territory and not the maps?

17. Apr 30, 2017

### ChrisVer

planck is not a detector... it's just a unit of something (if not the physicist)...
You can't say that the meter picks up the a wavelength....

this saying is irrelevant...

The photons from gamma ray bursts are not so energetic as you imagine: As far as I know they can reach up to ~100TeV and those I would guess are outliers... GRBs are a natural phenomenon that doesn't occur in laboratories but in space.

???

18. Apr 30, 2017

### oquen

Map is spacetime model which contains the spin networks or quantum fluctuations in the planck scale.

Territory is the real space in the planck scale which doesn't contain any spin networks.

Someday let's say we can probe the planck scale using wavelength that can fit inside it. Would we able to detect any spin networks (or quantum fluctuations) inside it? But spin networks are located in the maps, not the territory. Or if I'm confused. What is the map and territory in the case of general relativity and quantum spacetime and planck scales?

19. Apr 30, 2017

### nikkkom

It is not known for sure that space "really" exists down to those tiny scales. LQG and other "geometrodynamical" theories start with the idea that "maybe space is _not_ infinitely divisible?"

If we would be able to probe smaller scales, we would be able to detect what's happening there. That's the story of the last 100+ years of particle physics.

What is this "maps and territory" analogy? Maps = theories, territory = reality?

20. Apr 30, 2017

### oquen

There is an expression "don't mistake the maps for the territory". I don't know how to apply it to physics models. So maps = theories, territory = reality? Is that correct, or is that your guess? And does physics models fall under the "maps=theories" or "territory=realities"? If it's the former. But right now our physics models are our realities because we don't have other realities so what is officially the maps and territory here?