A scientist’s transmitter emits a wavelength

  • Context: Graduate 
  • Thread starter Thread starter ramcg1
  • Start date Start date
  • Tags Tags
    Transmitter Wavelength
Click For Summary

Discussion Overview

The discussion revolves around a scenario involving two scientists, One and Two, where One emits a long wave electromagnetic radiation and Two approaches it at a speed close to the speed of light. The conversation explores the implications of relativistic effects, the behavior of photons, and the transformation of energy during interactions, particularly focusing on the disintegration of a photon into an electron-positron pair and the subsequent events.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One emits a long wave electromagnetic radiation, which is observed by Two as he approaches at nearly the speed of light.
  • Two experiences fear upon seeing a high-energy gamma ray and activates a magnetic deflector, raising questions about the interaction of photons and the observer's perception.
  • Some participants argue that the space-time interval between an approaching photon and an observer is always zero, suggesting that the observer cannot react to the photon before it reaches them.
  • There is a discussion about the conditions under which a photon can decay into an electron-positron pair, emphasizing the need for conservation of energy and momentum.
  • Participants explore the implications of Einstein's clock synchronization on the simultaneity of emission and absorption events of photons.
  • Some argue that if an observer is accelerating away, they could potentially outrun the absorption of the photon, but this would require continuous acceleration.
  • There is a debate about the relationship between spacelike and lightlike events, with some participants asserting that simultaneous events for an observer cannot be both spacelike and lightlike.
  • References to Minkowski spacetime are made to clarify the nature of the events related to the photon and the observer.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the interaction between the observer and the photon, particularly regarding the implications of the space-time interval and the conditions for photon decay. There is no consensus on these points, and the discussion remains unresolved.

Contextual Notes

Participants highlight limitations in the scenario, such as the assumptions regarding the observer's frame of reference and the conditions necessary for photon interactions. The discussion also touches on advanced concepts in relativity that may not be fully accessible to all participants.

  • #31
OK, so it is not invariant, but it still still does not explain why the energy and momentum in one frame of reference is different to the energy and momentum in another frame of reference. If the object (whether a photon or some other kind of object) is in an intermediary position between the observers then it has two different energy levels at once. If the gamma ray interacts with an atomic nucleus how will Scientist One explain it?
 
Physics news on Phys.org
  • #32
Let's be specific: a gamma ray is absorbed by a nucleus. The energy and momentum of the gamma ray is transferred to the nucleus, which recoils and also gains some internal energy.

The amount of energy lost from the gamma ray is the same as the total energy (internal + energy of motion) gained by the nucleus according to scientist 1, and according to scientist 2.

Note that scientist 1 and 2 do not have to agree on the total energy of the gamma ray + nucleus. In fact, they do not. What they do agree about is that the interaction between the gamma ray and the nucleus does not change the total energy of the system (but they don't agree on what the numerical value of that initial energy was).

Note that we've said essentially the same thing before, so please think about this a little bit.
 
  • #33
The two scientists agree that the atom has certain "internal" energy levels (-13.6 eV, -3.4 eV, etc. for a hydrogen atom). They disagree about the atom's overall translational kinetic energy, and its momentum, because these depend on the velocity of the atom, which in turn depends on the reference frame. Therefore, they disagree about the atom's total energy (internal + kinetic).

In a photon absorption or emission process, their disagreement about the atom's total energy exactly compensates for their disagreement about the photon's energy. They both agree that the total energy of the system before the absorption or emission equals the total energy afterwards, although they disagree on its amount.
 
  • #34
“Let's be specific: a gamma ray is absorbed by a nucleus. The energy and momentum of the gamma ray is transferred to the nucleus, which recoils and also gains some internal energy.

The amount of energy lost from the gamma ray is the same as the total energy (internal + energy of motion) gained by the nucleus according to scientist 1, and according to scientist 2.

Note that scientist 1 and 2 do not have to agree on the total energy of the gamma ray + nucleus. In fact, they do not. What they do agree about is that the interaction between the gamma ray and the nucleus does not change the total energy of the system (but they don't agree on what the numerical value of that initial energy was).”

So Scientist One could detect his Long Wave Photon with an aerial but Scientist Two needs a nucleus to absorb the gamma ray.
 
  • #35
Clarifying Einstein synchronisation

MeJennifer said:
So then answer what the time difference is between the emittance and absorption of the photon for an Einstein clock synchronized frame of reference.
I say it is zero, what do you say?

Let's take a "practical" example, say we put clocks everywhere between us and some object X which is 5 light hours away from us, which, for symplicity's sake, is at rest relative to us.
We synchronize all clocks using Einstein's method.
Then say at 10:30 in the morning we emit a photon in the direction of the object X. What will be the time, on the local clock near the object, when the photon is absorbed?
Simple. It will be 3:30 in the afternoon. Einstein synchronisation means that if a light signal is sent from A to B and instantly returned back to A then B's clock at the moment of reception/return is set to half way between A's emission time and reception time. So in practice B starts by setting his clock to zero when he receives/retransmits the signal and when A sends a later message to B indicating A's two times, B can advance his own clock by the average of A's two times. "Relativity of simultaneity" comes about simply because from another inertial frame with respect to which A and B are in colinear uniform motion at the same velocity, the moment of signal reflection at B does not occur halfway between A's emission and reception.

Furthermore, it is especially important to note that reciprocal time dilation also arises naturally from this difference in synchronisation and thus simultaneity, without the need for any difference in actual clock rates !
 
Last edited:

Similar threads

  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 31 ·
2
Replies
31
Views
2K
  • · Replies 20 ·
Replies
20
Views
4K
  • · Replies 13 ·
Replies
13
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
Replies
9
Views
2K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 29 ·
Replies
29
Views
3K