Explore Projects Quantum Time Lab

Can a signal arrive before it is sent?

Inside a quantum device small enough and cold enough, interference can make the time an electron takes to cross come out negative. The Mesoscopic Time Group, led by Prof. P. Singha Deo, has followed that fact for a decade. Its answer, in print: a signal can be transmitted in negative time.

  • StatusPublished and ongoing
  • In print6 papers, a preprint and two Springer books
  • Led byProf. P. Singha Deo

The effect

The peak comes out before it goes in.

A pulse runs down a wire into a device with an interference dip. Watch the two peaks. Then deepen the dip.

This is standard scattering theory drawn live, not a result of ours: a pulse 6 picoseconds long, centred on the dip, with the device’s response time taken as 1 picosecond as an example. Early peaks of this kind have been measured for light pulses. The usual reading is that the pulse is reshaped and no message outruns its own front. The group reads it differently.

The pulse is on its way to the device.

The peak comes out early by
2.0 picoseconds
Share of the pulse that gets through
7.5 %
Clock: 0 is the incoming peak reaching the device
−1.0 picoseconds
White: the pulse going in. Gold: the pulse coming out, drawn at the same height so the peaks can be compared; it is really much fainter, and the earlier it comes, the fainter it gets. Dashed: where the pulse would be with no device. Illustration, not a simulation of a real device.

The idea

Three steps to negative time.

Mesoscopic

Small enough to stay quantum.

Between the atom and the everyday wire there is a middle scale. In a device that small and that cold, an electron crosses as a single wave, and the wave interferes with itself.

Negative time

Interference can run the clock backwards.

How long does the electron spend inside? Ask with a quantum clock and, at some energies, the answer comes out negative. The group traces this to a negative partial density of states, and has published where and why it appears.

The claim

A signal in negative time.

In 2019 the group published “Transmitting a signal in negative time”. It argues that the traversal time and the signal propagation time can both be negative, so that a signal can be propagated in negative time. Two books from Springer follow the route from there to time travel.

Read the paper

Where it stands

A bold claim, in print. An open test.

This is the authors’ interpretation of their own published mathematics. It is exciting, it is contested, and it remains open: no direct experimental test has been reported. We welcome alternative explanations and independent scrutiny.

In print

  • Negative partial density of states in mesoscopic systems. Annals of Physics, 2016.
  • Transmitting a signal in negative time. Results in Physics, 2019.
  • Time reversed states in barrier tunneling. Physica E, 2023. This one reports no evidence of causality being violated in tunnelling.
  • Negative local partial density of states. Journal of Condensed Matter, 2025.

Still open

  • A direct experiment that measures a negative signal time.
  • Whether a real message, and not only the peak of a pulse, can be sent early.
  • How it sits with relativity. The 2025 preprint argues that this local time behaves like the proper time of relativity; that argument has not been independently checked.

The experiment

What a test would have to see.

The quantities are measurable in principle. The time is read from how the phase of the wave leaving the device responds to a small, local change of voltage inside it.

Experiments on quantum-dot interferometers already measure the phase of electrons crossing a device. Turning that into a clean test of negative time is the open step. The same question, asked at the scale of the universe, is where our Atlas project begins.

Big Bang Atlas In the lab

The record

Read it for yourself.

  1. Journal article · 2025Negative Local Partial Density of StatesKanchan Meena, Souvik Ghosh & P. S. DeoJournal of Condensed Matter · 3(1), 16–21 · DOI 10.61343/jcm.v3i01.113
  2. Preprint · 2025Reinterpreting Landauer conductance, solving the quantum measurement problem, grand unificationKanchan Meena, Souvik Ghosh & P. Singha DeoarXiv:2512.09709
  3. Conference paper · 2025Multiple manifestations of negative partial density of statesKanchan Meena & P. S. DeoAIP Conference Proceedings · 3266, 020159
  4. Book · 2024Time Travel: A Reality in Mesoscopic PhysicsP. Singha Deo & Kanchan MeenaSpringer
  5. Journal article · 2023Time reversed states in barrier tunnelingKanchan Meena & P. Singha DeoPhysica E · 149, 115680
  6. Book · 2021Mesoscopic Route to Time TravelProsenjit Singha DeoSpringer
  7. Journal article · 2019Transmitting a signal in negative timeP. Singha Deo & Urbashi SatpathiResults in Physics · 12, 1506–1512
  8. Journal article · 2016Negative partial density of states in mesoscopic systemsUrbashi Satpathi & P. Singha DeoAnnals of Physics · 375, 491–514
  9. Journal article · 2009The Friedel sum rule at Fano resonancesP. Singha DeoJournal of Physics: Condensed Matter · 21, 285303
  10. Public explainer · 2025“We May Have Built the First Step Toward Real Time Travel — And It’s Already Peer-Reviewed”Souvik Ghosh · 6 May 2025Medium. An introduction to the authors’ interpretation of their research; the papers and books are the technical record.

Prof. P. Singha Deo, Kanchan Meena and the team Souvik Ghosh

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