# Identity in Physics – What can we learn?

- Identity in Physics

- Wednesday 5G

**Convener:** Paul Borrill

**Notes-taker(s):** Ryan Page

- Tags for the session - technology discussed/ideas considered

**Discussion notes, key understandings, outstanding questions, observations, and, if appropriate to this discussion: action items, next steps:**

Paul’s notes on topics discussed:

Identity in Physics: Steven French and Décio Krause. Identity in Physics: A Historical, Philosophical, and Formal Analysis. Oxford University Press, 2006 https://global.oup.com/academic/product/identity-in-physics-9780199278244

Identity in Philosophy: “The identity of indiscernibles”.

Identity and Individuality in Quantum Theory: http://plato.stanford.edu/entries/qt-idind/ [Very important read — recommended you read it all]

"Those great principles of sufficient reason and of the identity of indiscernibles change the state of metaphysics. That science becomes real and demonstrative by means of these principles, whereas before it did generally consist in empty words." ~ Gottfried Leibniz

Philosophy teaches us that this problem is already wicked, and is related to the Identity of Indescernables. This principle states that no two distinct objects or entities can exactly resemble each other (Leibniz's Law) and is commonly understood to mean that no two objects have exactly the same properties. The Identity of Indiscernibles is of interest because it raises questions about the factors that individuate qualitatively identical objects. This problem applies to the identity of data and what it means to have many substitutable replicas, as much as it does to Quantum Mechanics. This issue is of great importance to the complexity of humans interacting with their data, because it is unnecessary for a human to need to expend attention (or cognition) on any more than a single entity, no matter how many copies exist, as long has s/he can make the assumption that all the copies will eventually be made identical by the system.

See also: Katherine Hawley, How Things Persist.

How do things persist? Are material objects spread out through time just as they are spread out through space? Or is temporal persistence quite different from spatial extension? This key question lies at the heart of any metaphysical exploration of the material world, and it **plays a crucial part in debates about personal identity and survival.** Katherine Hawley explores and compares three theories of persistence -- endurance, perdurance, and stage theories - investigating the ways in which they attempt to account for the world around us. Having provided valuable clarification of its two main rivals, she concludes by advocating stage theory. Such a basic issue about the nature of the physical world naturally has close ties with other central philosophical problems. How Things Persist includes discussions of change and parthood, of how we refer to material objects at different times, of the doctrine of Human supervenience, and of the modal features of material things. In particular, it contains new accounts of the nature of worldly vagueness, and of what binds material things together over time, distinguishing the career of a natural object from an arbitrary sequence of events. Each chapter concludes with a reflection about the impact of these metaphysical debates upon questions about our personal identity and survival. Both students and professional philosophers will find that this wide-ranging study provides ideal access to the lively modern debate about an ancient metaphysical problem.

Time emerges from entanglement.

What is identity in physics – years ago moved to statistical physics – all particles are indistinguishable.

Thermodynamics is example

Indistinguishability goes all the way down.

All electrons are one electron – Feynman

Identity is at the heart of physics – Identity in physics book describes the heart of the problem.

Lee Smolin - Says it is a physics and philosophy problem.

Leibniz – the identity of the indiscernible. Insight into how know if something is the same as something else.

George Washington’s axe – is it the same axe? Theseus myth – the ship story. The ship of Theseus: https://en.wikipedia.org/wiki/Ship_of_Theseus

IF replace all the planks of the ship, is it the same ship?

Deep philosophical problem that is at the heart of the reasoning in physics. Modern digital world, - can create exact replicas of the object.

Want to make the object distributed. Reality of the object exists as many different replicas. Need to consider how propagate the change to one, to another.

Lattice variables – to make sure that all.

Simons institute – Berkeley – course on consistency. Can make things consistent locally, and cannot make them globally.

Digital version of Ship of Theseus

Entanglement is next issue – no-cloning theorem – see Wikipedia page

Cannot copy a quantum state – can only steal it.

If try to observe an entangled system, change it. Conserved quantities is related theorem – parity, momentum, etc. conserved.

Is information conserved – yes, but in interesting way. Shared information in quantum theory is where the information is. When make an observation, you

Entanglement: Nature of space time will change everything this year.

Google has 2 groups on quantum computers. Nobel prizes about quantum this year.

Quantum information theory – mutual information. It is a bipartite pair.

Entanglement is monogamous – only works between two parties (can compose that into larger objects, but idea is ripping apart idea about nature of space time.

After Einstein after general relativity – Murkowski space – space time is 4 dimensional.

How can you have these correlations between events that appear to happen faster than speed of light. 4 dimensional manifold challenge.

If I take a laser and shine it into object (parametric down conversion), and two photons get entangled.

Description of quantum entanglement apparatus. – called preparation of the measurement.

Information is negative of the entropy of the

Information is the answer to a yes no question. True in QM, true in Bayesian statistics, true for Shannon.

Bell states –

Einstein and Rosen paper – trying to resolve

Realizing that not living in 4 dimensional Murkowski space.

Back to apparatus description. Combine random generator number from two states.

Original Bell’s paper – were seeing correlations that were faster than speed of light. (c)

Puzzle of entanglement – Atoms are sending information to you in a spiral (described by Maxwell’s equation).

Electron spin can be measured, but when the electron is being exchanged back and forth, if had Murkowski background then would be able to detect time. There is no such thing as duration.

Biggest problem is the “Generals problem”

Computer science and physics – starting to see these deep problems of physics.

Exchange is lost of information (entropy).

Idea of speed, and that universe has a maximum speed is now being answered in terms of c, why is there a speed of light maximum.

Quantum provides random information. In electrical theory it is noise.

Photons and electrons are indistinguishable.

There is no such thing as single body.

When looking at stars – photon didn’t leave the star until it knew that your eye was waiting for it.

Information is mutual

Not predetermination

Time emerges from entanglement. The universe is stitched together with entanglement. This means that, if that is true – can send information exchanged without timeouts.

Taken the mutual information and leveraged it to attach a payload. That provides a piece of information that can remain persistent.

Think about these problems.

Reversible entanglement issue discussed.

Can you entangle a particle and have achievable predictable space?

Quantum key distribution is related. Fiber optic is doing that.

When you ask the question in entanglement

Can you have indirect observation – can you have a measurement - weak entanglement is using statistic analysis.

Descriptions of the slit experiment. “at the same time” is raising the Murkowski space.

What is the flawed assumption of the Murkowski space – look at EPR experiment. ER experiments – one solution is that can get a wormhole. Susskind and others have speculative, but seems that ER and EPR are the same thing.

These are the same phenomenon, but Einstein and Rosen didn’t recognize it.

The alternative to the slit experiment (going through both slits at the same time) is that time is going back and forth at the same time. It is the path of least action from Feynman diagrams. It is the same photon. Time is frozen in perpetuity between entangled

Can you entangle macro states? – Entanglement usually at atomic scales. What is really going on is that space time is stitched together by entanglement.

Coming to consensus – time emerges from entanglement. What mean for computer science and identity and irreversibility.

Can make time go backwards on a single link. Time does not exist.

How does this correlate with the second law of thermodynamics? Thermodynamic arrow of time. Issue.

Lowest level thing is the simplest. Carroll fond of notion of time.

Statistical question –

Space and time are the same thing –

1905 paper Einstein theory is about mirrors and clocks – one dimensional property.

3 dimensions may be

Emergent properties of systems are hard to consider.

Biology – notion of reversible differentiation,

How can we correlate – infinite dimensions that can explore. And some of those may be relevant to the workshop.

If these things are identical and can get information - how can things be hidden.

Dark matter and dark energy. What are they? We hide things now with quantum key distribution is a proven technology, but expensive. Once they are up and running they are secure. As soon as can move a key securely, can hide anything.

Speculation – if this is analyzed under the model of “no time” with photon going back and forth. If entangle photon – it is trapped. If given another photon – he and I are dark matter, but photon trapped in sub-time.

Tractor beam – cooling for electromagnetic cooling – if match frequencies and then raise frequency- it draws it toward. Closest to absolute zero with laser cooling.

Third thing to take from room – Entanglement is universal and substitutable.

Videos from Caltech – Stanford (Susskind), perimeter institute,

Starting thinking of time as a tree and be careful of how you establish the root (phase space issue).

Earth computing – How to distribute time and make sure that can be more resilient and using standard hardware.