# Questions tagged [unruh-effect]

This tag is for questions regarding to the Unruh effect (also known as the Fulling–Davies–Unruh effect), the hypothetical prediction that an accelerating observer will observe a thermal bath, like blackbody radiation, whereas an inertial observer would observe none. It was described by Stephen Fulling in 1973, Paul Davies in 1975, and William Unruh in 1976.

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### Unruh radiation "observed" by a particle undergoing Brownian motion

The Unruh effect is a basic result from the theory of quantum fields in curved space-time (a sort of precursor to quantum gravity) which can be thought of as describing how the ground state of ...
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### Davies & Unruh: vacuum temperature is proportional to acceleration. But $T$ is not a vector

Davies and Unruh showed that vacuum temperature is given by acceleration: $$T = \frac{\hbar a}{2 \pi k_\mathrm B c}.$$ But acceleration is a vector, temperature is not. If vacuum temperature produces ...
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### What is the physical interpretation of negative Unruh temperature?

Actually the Unruh temperature is vectorial since it is proportional to acceleration but derived for only one space dimension so at least positive and negative. What can negative Unruh temperature ...
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### Unruh modes inconsistent notation

The Unruh modes as defined in Sean Carroll's "Spacetime and Geometry" are: \begin{equation} h_k^{(1)} = \frac{1}{\sqrt{2\sinh(\pi \omega/a)}}\big(e^{\pi \omega/2a} g_k^{(1)} + e^{-\pi \omega/...
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### Unruh effect vacuum state

In Carroll "Spacetime and Geometry" I found the following explanation for why the analytically extended rindler modes share the same vacuum state as the Minkowski vacuum state: I can't ...
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### Unruh effect derivation

I was going through the derivation of the Unruh effect in chapter 5 of these lecture notes ("Lecture Series on Relativistic Quantum Information" by Prof Ivette Fuentes). On p.26 the author ...
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### Can Quantum Field Theory not handle accelerated frames of reference?

Since Quantum Field Theory can't handle gravity, and gravity is mathematically equivalent to acceleration (equivalence principle), does this mean Quantum Field theory can't handle accelerated frames ...
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### Does Unruh radiation potentially explain the Paradox of 'apparent non-radiation of charged particles in a gravitational field'?

The Wikipedia entry on 'Paradox of radiation of charged particles in a gravitational field' does not mention Unruh or Hawking radiation, but I don't see why they wouldn't provide a solution.... ...
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### Does the Unruh effect need the accelerating observer's Hilbert space to be smaller than the inertial one?

I've encounter two different approaches to the Unruh effect and I feel like they are not consistent with one another. Bogoliubov Transformation In this approach the basic statement is that the vacuum ...
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### Firewall in Rindler horizon

In arXiv:1409.1231 in section 3.5 above equation (3.34) Daniel Harlow says More precisely if the left and right wedges are completely uncorrelated, as in the state 3.33, then the typical difference ...
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### Usage of Rindler coordinates in studying Unruh Effect

When studying the Unruh Effect, Rindler coordinates are being used for the observer with constant acceleration. I am confused as to why Rindler coordinates are used as I do not see the motivation for ...
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### How can Unruh radiation ever be real?

It is speculated that Unruh radiation exists for accelerating observers in flat spacetime. A thermometer in the frame will point at a higher value than for someone in a stationary frame. In the ...
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A collection of accepted answers on Physics Exchange paint a seemingly inconsistent picture of Unruh radiation and it's isotropy. One of the most sophisticated answers, from Lubosz Motl, to the ...
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### Unruh temperature appears to depend on reference frame, how is this resolved?

I am wondering about observer-(in)dependence of Unruh temperature. Specifically, consider two observers, A and B, initially at rest in the same position. Then, at some point, A starts uniformly ...
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### What is the effect on temperature in a body when its velocity approaches the speed of light?

After reading the the following papers which explain why temperature must be frame invariant, I'm puzzled about the implications. https://zenodo.org/record/1334830#.YJ7lYVMXY0F https://inspirehep.net/...
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### How do you show that the Unruh Temperature between two inertial observers is zero?

As part of my undergraduate thesis, I'm trying to show that using massless scalar field, the Unruh effect between two inertial observers is zero. I'm using this book: "Introduction to Quantum ...
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### Interpretation of the nonuniqueness of vacuum of QFT in flat spacetime for a given inertial observer; No Lorentz transformation; No accelerated motion

Consider an inertial observer in flat spacetime with a choice of coordinates $(t,{\vec x})$. This observer can expand a quantum field $\hat{\phi}$ in more than one complete set of orthonormal modes. ...
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### What is the interpretation of non-uniqueness of field expansion in flat spacetime?

Scalar field expansion in terms of plane wave modes is given by $$\phi(x)=\int\frac{d^3{\vec p}}{\sqrt{(2\pi)^{3}2\omega_{\vec p}}}\left(a_{\vec p}e^{-ip\cdot x}+a_p^\dagger e^{+ip\cdot x}\right)$$ ...
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### Unruh effect on rotating galaxies?

According to the Unruh effect, an accelerating observer will experience a thermal bath. This is equivalent to Hawking radiation. If we applied this to a spinning galaxy, I wonder if this thermal bath ...
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### Can the inertial observer "see" the Unruh accelerated observer's vacuum?

The unruh process is asymmetric. The inertial observer is in his vacuum V0 and the accelerated observer measures $\langle V_0|N|V_0 \rangle$ and sees particles. He is not in his vacuum environment. I ...
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### For Hawking radiation, is the scalar field $\phi$ assumed to be in the Unruh vacuum state?

In Hawking's paper "Particle Creation by Black Holes" I'm not really able to pick apart what vacuum state Hawking is assuming the field $\phi$ to be in. The paper "Hawking radiation as ...
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### Isn't Unruh effect against the equivalence principle?

Doesn't the Unruh effect violate EP? Since the temperature of an absolutely accelerating reference frame would be different from an inertial one according to this effect, then one finds a criterion to ...
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### Unruh particles

When we accelerate, an event horizon forms behind us resulting in Unruh radiation. In this kind of scenario, the existence of the radiation particles themselves is observer dependent. My question is: ...
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### Is the Unruh effect a special relativistic effect or a general relativistic effect?

If an observer moves in an accelerated frame in flat spacetime, the vacuum looks like a thermal distribution of particles to that observer. This is the Unruh effect. Is it a special relativistic (SR) ...
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### Why a mode on Minkowsky SpaceTime becomes two modes on Rindler Spacetime

----I am a student on Quantum Computing--- For the whole undertanding of "Tetrapartite entanglement measures of GHZ state with uniform acceleration" by Qiang Dong. https://doi.org/10.1088/...
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### How does the Unruh effect create particles?

I've read that the Rindler horizon cuts off access to fundamental quantum fields and leads to a mixing of positive and negative frequencies via the Bogoliubov transformations. But here is where I have ...
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### Can Unruh particles be blocked on their way from the horizon?

Can you shield yourself from Unruh particles? In an old answer to a different question, Ron Maimon says yes: You should think of the radiation as coming from the horizon--- if you place a ...
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In case of a black hole, the direction of the Hawking radiation is from the horizon to the observer. The corresponding effect in the Rindler spacetime is the Unruh radiation. Intuitively, a rapidly ...
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### Does an object falling into a black-hole get destoyed by Unruh radiation?

My basic understanding of the Unruh effect is that an accelerating observer will experience black-body radiation proportional to the magnitude of the local acceleration, while an observer in an ...
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### Why does annihilation and creation operator mix in curved spacetime?

When doing QFT in curved spacetime we do Bogoliubov transformation to find one set of annihilation and creation operators in terms of others. In the paper Particle creation by black holes Hawking ...
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### Rindler horizons as limits

Consider a worldline $\bf{W}$ that accelerates at constant rate $\alpha$ only between $-t_0$ and $t_0$, and is otherwise inertial before $-t_0$ and after $t_0$. For all finite $t_0$ there is no ...
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### Does Hawking radiation lead to black hole evaporation / reduction of black hole mass?

As I understand, Hawking radiation leads to black hole evaporation, resp. a black hole would lose mass due to that effect. Now Hawking radiation is very similar to Unruh radiation, i.e. some (apparent)...
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### Unruh effect for finite period of low acceleration

I am trying to find out about the Unruh effect in the case of a finite period of low acceleration. I understand the following: The calculation leading to a thermal spectrum at the Unruh temperature ...
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### What is the experimental evidence - direct or indirect - for Hawking or Unruh radiation?

I'm wondering what evidence exists, direct or indirect, for Hawking or Unruh radiation. I believe one of the initial goals for the Fermi LAT mission was to look for evaporating microscopic black ...
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### Ways to derive black-body radiation in Unruh effect

I know two ways to derive black-body radiation in Unruh effect and they are: Using Bogoliubov coefficients (N. D. Birrell and Paul Davies) Using Page approximation (David J. Toms and Leonard Parker) ...
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### On the necessity of an event horizon for the Hawking-Unruh effect

I first explain my reasoning. I know that a Schwarzschild metric is the right metric outside any spherical object, but I also know that it is correct in the empty space. So I thought: why we don't ...
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### Hawking radiation and Unruh effect

I recently read about the Hawking effect and I noticed that formally, in its general lines, the derivation is very similar to that of the Unruh eff. In the latter case we write the Fock states in a ...
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### Is there somesort of "recipe" to check if an spacetime exibit the Unruh effect?

Firstly I don't know for sure if this question makes a solid sense, concerning the physical phenomena. I) Unruh Effect Now, we have then the Unruh effect which appears just by considering the ...
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### Minkowski space and Rindler spaces, What's relation?

To describe the dynamic of a qubit one can use the Minkowski cordinates, But when that qubit is accelerated with Unruh acceleration we need Rindler cordinate . So, what is UNRUH acceleration? and ...
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### Are Bremsstrahlung and the Unruh effect equivalent?

This paper argues that the absorption and emission rates from and to the thermal Unruh bath of a proton viewed in a coaccelerated frame is equal to the emission rated viewed from an inertial observer. ...
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### What are zero-energy Rindler photons?

In the discussion of the Unruh effect and Bremsstrahlung (e.g. here) I always come across "zero-energy Rindler photons". What exactly are these? Shouldn't a zero-energy photon correspond to a static ...
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### Why to we take the Minkowski vacuum to calculate the thermal Unruh distribution?

Looking at a derivation for the Unruh effect, this generally ends with a calculation of the particle distrubution: $$\langle{0_M}|b^\dagger b|0_M\rangle=\frac{1}{e^{\hbar\omega/k_BT_U}-1}$$ where $b$ ...
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### Do Rindler horizons evaporate?

It is thought that black holes radiate via Hawking radiation and consequently evaporate. Rindler horizons too emit radiation. Are they also thought to undergo a similar process of evaporation?
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### Question about path integral step of the rindler decomposition

In most papers where I've read about Rindler decomposition and the Unruh effect ( see for example  or ) they start by saying that they want to find the wavefunction of the vacuum state in the ...
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### Does thermal state in Rindler spacetime correspond to Minkowski vacuum?

We know that the Minkowski vacuum corresponds to the thermal state in a Rindler wedge at Unruh temp. But does the thermal state in one Rindler wedge at Unruh temperature uniquely map to the Minkowski ...
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### Rindler-Fulling Quantization - Rindler mode expansion of $\phi$: why are we ignoring the Past and Future Wedges?

I am following along Chapter 2 of Takagi's Vacuum noise and stress induced by uniform accelerator. I am at the point of performing the Rindler-Fulling Quantization of a real scalar field, where you ...