To measure a Planck length would require a black-hole photon?

[swampwiz]

I was viewing this video in which the narrator says that the energy of a photon that could discern a Planck length would require a photon of such high energy that it would be a de factor black hole. Is this accurate?

 

[PeroK]

The video itself looks quite reasonable, but that particular statement is fairly meaningless. An energetic photon isn't a black hole.

 

[swampwiz]

The video itself looks quite reasonable, but that particular statement is fairly meaningless. An energetic photon isn't a black hole.

Maybe it's a Kugelblitz instead ?

 

[PeroK]

Maybe it's a Kugelblitz instead ?

It's not that either. It's just a very energetic photon you need.

 

[swampwiz]

It's not that either. It's just a very energetic photon you need.

The idea seems to be that the photon would have an energy so high, and concentrated into a space so small, that there would be enough equivalent mass to create a microscopic black hole.

 

[PeterDonis]

The idea seems to be that the photon would have an energy so high, and concentrated into a space so small, that there would be enough equivalent mass to create a microscopic black hole.

A photon isn't "concentrated into space"; it can't be localized the way a particle with nonzero rest mass can be. So this argument, although it sounds plausible (since it is mathematically true that a black hole with Schwarzschild radius equal to the Planck length does have energy equal to the Planck energy, which is, heuristically, the energy a photon would have to have to allow it to pin down the position of an object to within a Planck length), is not valid.

 

[PeroK]

The idea seems to be that the photon would have an energy so high, and concentrated into a space so small, that there would be enough equivalent mass to create a microscopic black hole.

I understand the idea - it's simply mistaken. A photon is not localised, hence cannot be a black hole.

 

[PeterDonis]

the energy of a photon that could discern a Planck length

It is worth noting, in addition to the other objections that have already been made, that this energy (the Planck energy) is way, way above the electroweak symmetry breaking energy, so "photon" is no longer a valid concept anyway; at this energy, the appropriate quantum fields would be the "bare" electroweak fields ($W_1$, $W_2$, $W_3$, and $B$), all of which are massless at this energy. So even the general idea of localizing anything to within a Planck length is probably not valid.

 

[swampwiz]

Here's another video discussing this. He talks about the black hole at around 15:00.

 

[PeterDonis]

Here's another video discussing this. He talks about the black hole at around 15:00.

Still the same basic argument, and the same issues that have already been raised.

The proper source from which to learn physics is textbooks and peer-reviewed papers, not pop science videos.

 

[PeterDonis]

The OP question has been answered. Thread closed.